Infection

Question 1

@# 2.A 38-year-old male with Human Immunodeficiency Virus (HIV) stopped taking his retrovirals 6 months ago and now presents with confusion. CT brain shows non-enhancing hypodensities, with apparent dilated perivascular spaces, although these were not present on a CT brain from 2 years ago. What is the most likely cause?

A. Cryptococcus

B. Progressive multifocal leukoencephelopathy

C. Tuberculosis

D. CMV encephalitis

E. Toxoplasmosis

Answer 1

A. Cryptococcus

More commonly cryptococcus meningitis but Cryptococcus or gelatinous pseudocysts reside in dilated perivascular spaces

Question 2

30. In herpes simplex virus (HSV) type 1 encephalitis:

A. Early CT findings include hyperdensity in one or both temporal lobes

B. Avid contrast enhancement in the temporal lobes is often present on C7

C. MR shows avid contrast enhancement in the temporal lobes

D. The basal ganglia are typically spared

E. Signal abnormalities are usually persistent even after drug treatment

Answer 2

D. The basal ganglia are typically spared

Early CT findings may show medial temporal hypodensity. Areas poorly enhance on CT and MR. Signal abnormalities often decrease in response to treatment.

Question 3

@# 45. Which is the most common location for toxoplasmosis?

A. Basal ganglia

B. Frontal lobe

C. Occipital lobe

D. Temporal lobe

E. Brainstem

Answer 3

A. Basal ganglia

75% of cases are in the basal ganglia.

Question 4

46. Progressive multifocal leukoencephalopathy has a predilection for:

A. Cerebellum

B. Parietal lobe

C. Occipital lobe

D. Parieto-occipital region

E. Frontal lobe

Answer 4

D. Parieto-occipital region

PML has a predilection for the parieto-occipital region.

Question 5

71) Sequelae and complications of meningitis that may be identified on contrast-enhanced CT of the brain in the acute phase of the disease include all but which of the following?

a. venous sinus thrombosis

b. leptomeningeal enhancement

c. encephalomalacia

d. ring-enhancing mass lesion

e. infarction

Answer 5

c. encephalomalacia

Diagnosis of meningitis is made by clinical examination and examination of CSF.

Imaging is reserved for complications and to identify contraindications to lumbar puncture.

The mechanism of spread is usually haematogenous, common organisms being Neisseria meningitidis (meningococcus) in young adults, Escherichia coli and Haemophilus influenzae.

Complications that can be identified on CT include subdural empyema (sterile effusion can be seen with H. influenzae), venous sinus thrombosis, infarction, cerebritis and abscess formation.

Leptomeningeal thickening and enhancement may be seen, but its absence does not exclude a diagnosis of uncomplicated meningitis.

CT may also identify a potential source of infection such as otitis media, mastoiditis, sinusitis or orbital cellulitis.

Question 6

3) A 37-year-old man with AIDS presents with confusion, lethargy and memory loss. CT of the brain demonstrates multiple supratentorial enhancing masses. Which imaging feature favours a diagnosis of toxoplasmosis rather than primary CNS lymphoma?

a. subependymal distribution

b. lesions hyperdense on unenhanced CT

c. lesion size .3 cm

d. hypovascularity on MR perfusion study

e. increased uptake of thallium-201 on SPECT

Answer 6

d. hypovascularity on MR perfusion study

Toxoplasmosis is the most common cause of a cerebral mass lesion in patients with AIDS.

Typical appearances are of multiple, hypoattenuating, ,2 cm lesions with a predilection for the basal ganglia.

Lymphoma is the second commonest mass lesion, with characteristic features including hyperdense lesions (though less frequently than in non-AIDS lymphoma) in a periventricular location with subependymal spread.

Lesions in both conditions may show solid or ring enhancement.

Haemorrhage is unusual in lymphoma but may be seen in toxoplasmosis, particularly following treatment. Thallium scanning may be useful to distinguish the two if there is diagnostic uncertainty.

CNS lymphoma is thallium avid whereas toxoplasmosis does not show uptake.

MR perfusion studies may also help to differentiate the two conditions.

Lymphomas demonstrate increased perfusion relative to surrounding tissue, while toxoplasmosis is hypovascular.

Differentiation is important, as early radiation therapy confers a significant survival advantage in CNS lymphoma.

Question 7

37) A 39-year-old man known to have HIV and with clinically deteriorating dementia undergoes MRI of the brain with a provisional diagnosis of HIV encephalopathy. Images show abnormal high signal on T2W and FLAIR images affecting the white matter, caudate nucleus and basal ganglia on a background of brain atrophy. Which additional MR characteristic of these lesions is likely to suggest progressive multifocal leukoencephalopathy over HIV encephalopathy?

a. frontal white matter preponderance

b. clustering around the basal ganglia

c. involvement of subcortical U fibres

d. areas of haemorrhagic necrosis

e. enhancement with intravenous gadolinium

Answer 7

c. involvement of subcortical U fibres

HIV encephalopathy is a progressive subcortical dementia caused by direct infection of the central nervous system by HIV.

It is therefore not an opportunistic infection and is seen in up to 60% of AIDS cases.

The most striking feature is cerebral atrophy and diffuse myelin pallor, manifested as ill-defined, confluent areas of high signal in the white matter on T2W sequences or low attenuation on CT.

Changes are usually bilateral but asymmetrical, with characteristic sparing of the grey matter.

Progressive multifocal leukoencephalopathy occurs in only 2–4% of AIDS cases and is a reactivation of the JC (John Cunningham) virus, resulting in destruction of oligodendrocytes.

The most common location is posterior whereas HIV encephalopathy is more commonly frontal; however, this is an unreliable discriminator.

Progressive multifocal leukoencephalopathy characteristically involves the subcortical U fibres and also affects grey matter.

It has a very poor prognosis, death occurring within 2–5 months.

Question 8

84) A 30-year-old woman presents acutely with seizures, fever and headache, followed by rapid deterioration to coma. Emergency MRI shows asymmetrical swelling of the anterior temporal lobes on T1W images. T2W images reveal concordant asymmetrical but bilateral areas of high signal in the anterior temporal lobes, insular cortices and hippocampi. There is no enhancement following administration of intravenous gadolinium. What is the most likely condition?

a. lymphoma

b. HIV encephalitis

c. cytomegalovirus encephalitis

d. herpes simplex encephalitis

e. toxoplasmosis

Answer 8

d. herpes simplex encephalitis

Herpes simplex virus is the most common cause of fatal endemic encephalitis, often leaving survivors with severe memory and personality problems. Both oral (type 1) and genital (type 2) strains may produce encephalitis with a multimodal distribution, affecting neonates (due to cross-infection with type 2 from the mother during birth), children and adults. Childhood and adult infection is caused by the type 1 virus and results in fulminant necrotizing encephalitis presenting with acute confusion and deteriorating rapidly to coma. Focal neurological deficits are seen in only 30% of cases. The virus asymmetrically affects the temporal lobes, insula, orbitofrontal region and cingulate gyrus, causing oedema. This is seen as high signal on T2W/FLAIR images, with DWI appearances variable depending on the presence of infarction. The putamen is characteristically spared, and the areas of encephalitis typically do not show enhancement on CTor MRI.

Question 9

97) In brain imaging performed to characterize a chronic subdural collection, which feature is more likely to favour a diagnosis of subdural empyema over a sterile effusion?

a. isointense MR signal on T1W images

b. hyperintense MR signal on T2W images

c. subfalcine herniation

d. restricted diffusion on MR DWI

e. low attenuation on CT

Answer 9

d. restricted diffusion on MR DWI

Abscess cavities and empyemas are homogeneously hyperintense on MR DWI and low on ADC map due to the increased viscosity of the purulent material that they contain, resulting in restricted diffusion of water. Sterile effusions are hypointense on DWI and have an ADC appearance similar to that of CSF due to their lower viscosity and free macro-diffusion of water. Diffusion images can therefore be important when deciding whether to intervene surgically or conservatively manage subdural collections, as empyema requires timely surgical drainage. Contrast enhancement of the wall of the collection may be seen on CT and MRI, but its absence does not exclude the diagnosis of a purulent collection. Likewise, one may expect to see additional mass effect with an infected collection, but this too is not sensitive enough to exclude infection by its absence.

Question 10

14 A young man with known HIV and a CD4 lymphocyte count of 300 cells/ml develops neurological symptoms. MR Imaging reveals ischaemic infarcts within the distributions of the perforator arteries of the basal ganglia and the middle cerebral artery. What infective aetiology could account for these findings?

(a) Epstein-Barr virus

(b) Toxoplasmosis

(c) Cryptococcus

(d) Syphillis

(e) Polyomavirus

Answer 10

(d) Syphillis

Neurosyphillis causes a large and medium sized vessel arterltis, which can result in infarcts in the brain stem, basal ganglia and MCA territory. Syphillitic gummas are a further imaging manifestation.

Question 11

(Ped) 58 A term day 1 baby has a seizure on the neonatal unit. Cranial US shows hyperechoic periventricular areas. A subsequent CT shows multiple punctuate calcifications in a symmetrical periventricular distribution. Which congenital infection is the most likely cause of these appearances?

(a) CMV

(b) Herpes simplex

(c) HIV

(d) Rubella

(e) Toxoplasmosis

Answer 11

(a) CMV

Congenital infections include HIV and TORCH (TOxoplasmosis, Rubella, CMV, and Herpes simplex).

The findings described are classic for CMV (CT is adequate for diagnosis in up to 70% cases). There may be associated polymicrogyria.

Toxoplasmosis and rubella calcification is distributed around the basal ganglia and in the parenchyma.

HIV produces diffuse atrophy. Basal ganglia calcification may appear at 1 year.

Question 12

36 An immunocompromised patient develops progressive neurological deficits. Confluent, bilateral white matter lesions are seen in the parieto-occipital region on MR imaging. Progressive multifocal leukoencephalopathy is suspected. Which of the following conditions is not known to be associated with PML?

(a) Whipple disease

(b) Migraine

(c) AIDS

(d) Cancer

(e) Sarcoid

Answer 12

(b) Migraine

Other associated conditions include: autoimmune diseases, immunosuppressive therapies, Lympho- and myeloproliferative disorders, nontropical sprue, transplantation, and tuberculosis

Question 13

44 A young man presents with a fever, stiff neck and headache. CSF studies reveal a raised protein concentration, a predominance of polymorphonuclear leukocytes and a low glucose concentration. Which of the following would be the most atypical imaging appearance for the most likely diagnosis?

(a) Normal unenhanced CT

(b) Normal unenhanced MR

(c) Hypointense plaques on T2W MR imaging

(d) Obliteration of the basal cisterns on contrast-enhanced CT

(e) Increased attenuation of the subarachnoid space on unenhanced CT

Answer 13

(c) Hypointense plaques on T2W MR imaging

Hyperintense, rather than hypointense plaques are a recognised T2 finding in bacterial meningitis. Most cases of bacterial meningitis will have normal non-enhanced MR imaging.

Question 14

27 A patient with known HIV develops neurological symptoms and a CT head examination is performed. Multiple ringenhancing lesions are seen. What imaging features would support diagnosis of toxoplasmosis > lymphoma?

(a) Hyperdense on unenhanced CT imaging

(b) Eccentric enhancing nodule

(c) Callosal involvement

(d) Subependymal spread

(e) Periventricular location

Answer 14

(b) Eccentric enhancing nodule

An eccentric enhancing nodule may be seen in cases of toxoplasmosis, but is rare in lymphoma. Callosal involvement, ependymal spread and high attenuation on unenhanced CT im-aging are typical features of lymphoma.

Question 15

50 A neonate is noted to have cataracts, microcephaly, basal ganglia calcification and a patent ductus arterious.
Which of the following in utero infections could explain all of these features?

(a) Toxoplasmosis

(b) Rubella

(c) Cytomegalovirus

(d) Herpes simplex

(e) HIV

Answer 15

(b) Rubella

In addition, rubella is associated with hearing loss, autism, pigmentary retinopathy, vasculopathy, pulmonic stenosis, and hepatosplenomegaly.

Question 16

66 An immuno-compromised patient presents with symptoms of encephalitis. MR imaging is performed and primary CNS lymphoma is considered likely. Which of the following features would be unusual for this diagnosis?

(a) Supratentorial location

(b) A large, discrete solitary lesion

(c) Ring enhancement with i. v. gadolinium

(d) A peripheral rim of high signal on T2WI

(e) Decreased uptake of thallium-201 on SPECT imaging

Answer 16

(e) Decreased uptake of thallium-201 on SPECT imaging

CNS lymphoma has increased uptake of thallium-201 on SPECT imaging.

Question 17

28. The husband of a 33 year old woman takes her to the local accident and emergency department, stating that she is becoming acutely confused and is not her normal self. Her past medical history is unremarkable apart from a flu-type illness a few days earlier. Her GCS is 13 (E – 4, V – 3, M – 6). Initial non-contrast-enhanced CT of the brain shows low-density change within the left temporal lobe. MRI demonstrates abnormal low signal on T1 and high signal on T2 within the left temporal cortex. The insula is involved but there is sparing of the putamen. There is mild mass effect with partial effacement of the lateral ventricles. What is the most likely diagnosis?

a. Herpes simplex encephalitis

b. Low-grade glioma

c. Brain abscess

d. Post-viral leukoencephalopathy

e. Dural sinus thrombosis leading to cerebral infarction

Answer 17

28. a. Herpes simplex encephalitis (HSE)

There are two main types of herpes simplex virus (HSV) – HSV type I and HSV type II. Type I (oral herpes) tends to affect older infants, children and adults whereas type II (genital herpes) is the usual cause of HSE in neonates.
HSE is a necrotising meningoencephalitis which has a predilection for the limbic system (temporal lobes, insula, cingulated gyri). Characteristically, there are poorly defined areas of low attenuation in one or both temporal lobes/limbic system on unenhanced CT, low signal on T1 (gyral oedema) and high signal on T2. The T2 high signal typically spares the putamen and forms a sharply defined border.
Changes may initially appear unilateral but contralateral disease invariably follows. This sequential bilaterality is characteristic of HSE. Haemorrhage is typically a late finding. Mortality ranges from 30% to 70% but is reduced with early antiviral therapy.

Question 18

@# 31. A patient known to have AIDS presents with increasing malaise and confusion. CT brain shows multiple cerebral hypoattenuating nodular lesions with varying degrees of surrounding oedema and mass effect. There is lesional enhancement post-contrast administration. Which of the following conditions can be confidently removed from the differential diagnosis?

a. Tuberculosis

b. Pyogenic abscesses

c. Progressive multifocal leukoencephalopathy

d. Lymphoma

e. Toxoplasmosis

Answer 18

31. c. Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy affects about 4% of AIDS patients and is caused by reactivation of ubiquitous JC papovavirus. This causes lysis of oligodendrocytes resulting in demyelination. CT shows single or multiple hypoattenuating white matter lesions without oedema/mass effect. There may also be grey matter lesions in the thalamus/ basal ganglia from involvement of traversing white matter tracts. The majority of patients show mild cortical atrophy. The condition carries a poor prognosis with death within two to five months.
All the other conditions listed will have various amounts of surrounding oedema/mass effect and enhance post-contrast.
Toxoplasmosis is the most common cerebral mass lesion in AIDS and is two or three times more frequent than lymphoma (the second most common cause of a CNS mass in AIDS). Multiple lesions suggest toxoplasmosis over lymphoma, however when there is a solitary lesion the probability of lymphoma is at least equal to that of toxoplasmosis.

Question 19

46. A 33 year old male with no significant past medical history presents with headache, drowsiness and confusion. CT shows a hypodense lesion with a smooth regular wall centred over the left lentiform nucleus. There is surrounding oedema and mass effect with effacement of the ipsilateral Sylvian fissure. On T2-weighted MR imaging, the lesion is hyperintense and is surrounded by a hypointense rim and hyperintense oedema. There is peripheral enhancement post-contrast injection, and diffusion-weighted imaging demonstrates restricted diffusion within the lesion. What is the most likely diagnosis?

a. Glioblastoma multiforme

b. Pyogenic abscess

c. Toxoplasmosis

d. Lymphoma

e. Metastasis

Answer 19

46. b. Pyogenic abscess

The differential diagnosis for a solitary ring-enhancing lesion of the brain includes (‘MAGICAL DR’): Metastasis; Abscess; Glioma/Glioblastoma multiforme; Infarction; Contusion; AIDS (toxoplasmosis); Lymphoma (often AIDS-related); Demyelinating disease; Resolving haematoma/Radiation necrosis.
Classically, abscesses are located at the corticomedullary junction in the frontal and temporal lobes. The most common causative organism is Streptococcus. The wall is generally smooth and regular with relative thinning of the medial wall secondary to a poorer blood supply from white matter (neoplastic lesions usually have a thick, nodular, irregular rim).
In this scenario, the enhancing, T2-hypointense rim suggests abscess. Restricted diffusion is also highly suggestive of an abscess.
Lymphoma may be hyperdense on CT due to a high nuclear-to-cytoplasmic ratio and typically shows solid homogeneous enhancement in immunocompetent patients.

Question 20

@# 57. A four month old male undergoes investigation for microcephaly and hearing loss. Unenhanced CT brain shows several periventricular subependymal cysts and multiple coarse periventricular and parenchymal white matter calcifications. There is diffuse hypoplasia of the cerebellum. What is the most likely diagnosis?

a. Tuberous sclerosis

b. Sturge–Weber syndrome

c. Cytomegalovirus infection

d. Venous sinus thrombosis

e. Congenital rubella

Answer 20

57. c. Cytomegalovirus infection

This is the most common intrauterine infection and the leading cause of brain disease and hearing loss in children.

Typical imaging findings include periventricular subependymal cysts representing focal areas of necrosis and glial reaction, periventricular postinflammatory calcifications, scattered calcifications in basal ganglia and brain parenchyma, microcephaly due to disturbance of cell proliferation and hypoplasia of the cerebellum. There may also be lissencephaly, cortical dysplasia, polymicrogyria and schizencephaly due to disturbed neuronal migration.

Question 21

QUESTION 2
A 33-year-old HIV-positive woman presents with increasing headache and confusion. On examination she is pyrexial and has left leg and right facial weakness. A CT head demonstrates multiple lesions measuring between 2 and 4 cm which are predominantly situated at the corticomedullary junction. These lesions have a thin enhancing rim as well as associated oedema and local mass effect. Which one of the following is the most likely diagnosis?

A Cryptococcosis

B Histiocytosis

C HIV encephalopathy

D Multiple cerebral metastases

E Toxoplasmosis

Answer 21

E Toxoplasmosis

Question 22

QUESTION 4
A 41-year-old woman presents with a 2-day history of disorientation and headache. She describes general malaise over the preceding week. No localizing neurological signs are elicited on examination. She has a CT head which is normal, but her symptoms deteriorate and she has a generalised tonic clonic seizure the following day. Which of the following findings would you expect to see on a repeat CT scan?

A A thin fluid collection in the interhemispheric fissure which has an enhancing rim

B Bilateral rims of low attenuation overlying the temporoparietal cortex

C Low attenuation in the frontal and temporal lobes with patchy gyriform enhancement postcontrast

D Multiple large low attenuation areas within the white matter

E Ovoid lesions of high T2 signal in the periventricular white matter orientated perpendicular to the lateral ventricles

Answer 22

C Low attenuation in the frontal and temporal lobes with patchy gyriform enhancement postcontrast

The clinical details are highly suggestive of herpes simplex encephalitis, which often follows a nonspecific viral infection. CT may be normal in the first 3—5 days

Question 23

QUESTION 22
A 53-year-old man is admitted with fever, headache and drowsiness. A CT head reveals a low attenuation lesion at the corticomedullary junction of the left frontal lobe with an enhancing rim and some surrounding low attenuation change. Opacification of his paranasal sinuses is also noted. What is the most likely diagnosis?

A Metastasis

B Primary cerebral lymphoma

C Pyogenic abscess

D Toxoplasmosis

E Tuberculous abscess

Answer 23

C Pyogenic abscess

Pyogenic brain abscesses usually arise by direct infection, penetrating trauma or haematogenous spread. In this case there is evidence of sinusitis which has led to direct intracranial spread.

Question 24

QUESTION 28
A 19-year-old HIV-positive man is admitted with headaches, confusion and disorientation. He is mildly pyrexial. A CT brain reveals multiple hypodensities, particularly in the brainstem and in the periventricular white matter. There is some ependymal enhancement postcontrast. What is the most likely cause for these findings?

A CMV encephalitis

B Cryptococcosis

C HIV encephalitis

D Toxoplasmosis

E Tuberculosis

Answer 24

A CMV encephalitis

Cerebral CMV infection usually presents as encephalitis, ventriculitis, infarcts or meningitis. The typical sites for encephalitis are the brainstem and periventricular white matter.

Cryptococcus usually causes a meningitis which is poorly seen on imaging.

HIV encephalitis manifests as demyelination and gliosis characteristically in the centrum semiovale.

Toxoplasmosis is characterised by ring-enhancing lesions at the corticomedullary junction and in the basal ganglia and thalamus.

Lastly, tuberculosis causes multiple granulomata (initially hypodense on CT with little enhancement but subsequently calcify following treatment) and leptomeningeal disease.

Question 25

QUESTION 50
A 44-year-old HIV-positive woman is admitted to hospital with worsening headaches and drowsiness. CT reveals several ovoid high attenuation lesions in the periventricular white matter and the basal ganglia. Some of the lesions appear to be abutting the ventricles. The lesions display homogeneous enhancement postcontrast although some of the larger ones have a low attenuation centre. There is no evidence of haemorrhage or calcification. Which one of the following is the most likely diagnosis?

A Multiple metastases

B Multiple pyogenic abscesses

C Multiple tuberculous abscesses

D Primary cerebral lymphoma

E Toxoplasmosis

Answer 25

D Primary cerebral lymphoma

In an HIV-positive patient, the most important differential diagnoses are lymphoma and toxoplasmosis. Toxoplasmosis typically displays a thin rim of enhancement.

Question 26

(Ped) QUESTION 50
A 5-year-old child presented 1 week ago with bacterial meningitis and is now persistently pyrexial with new onset seizures. An MRI shows frontal leptomeningeal enhancement, with enhancing material within the subdural space. The signal from the subdural space is higher than CSF in both the Tlw and T2w images. What is the most likely diagnosis?

A Cerebral abscess

B Cerebritis

C Subdural effusion

D Subdural empyema

E Ventriculitis

Answer 26

D Subdural empyema

Increased signal within the subdural space relative to CSF on both Tlw and T2w images is consistent with a subdural empyema. This is likely to require urgent drainage, whereas subdural effusions do not need surgical treatment and will resolve as the meningitis is treated.

Question 27

QUESTION 58
An 18-year-old HIV-positive man is admitted to hospital with headaches, drowsiness and increasing confusion. A CT head reveals dilatation of the ventricles, hyperdensity of the basal cisterns and several small isodense and hypodense lesions at the corticomedullary junction. Postcontrast images show enhancement of the basal cisterns and ring enhancement of the corticomedullary lesions. What is the most likely diagnosis?

A Cryptococcosis

B Leptomeningeal metastases

C Sarcoidosis

D Toxoplasmosis

E Tuberculosis

Answer 27

E Tuberculosis

The imaging appearance describes basal leptomeningeal involvement in CNS tuberculosis as well as the presence of tuberculomas. Sarcoidosis may have similar appearances but tuberculosis (especially with the presence of tuberculomas or abscesses) is more likely in HIV infection.

Question 28

QUESTION 65
A 41-year-old HIV-positive man undergoes an MRI brain to investigate headaches, fever and confusion. This shows multiple foci in the basal ganglia and brainstem which are of low signal on Tlw and high signal on T2w images. There is no significant associated oedema and no enhancement is seen postcontrast. What is the most likely diagnosis?

A Cryptococcosis

B Cytomegalovirus infection

C HIV encephalopathy

D Lymphoma

E Progressive multifocal leukoencephalopathy

Answer 28

A Cryptococcosis

Cryptococcosis is the second commonest opportunistic CNS infection in AIDS. Early features include dilated perivascular spaces with the development of ciyptococcomas as the disease progresses.

Question 29

QUESTION 70
A 40-year-old woman is known to be HIV positive with a CD4 count of 45 cells/pL. She presents with progressive weakness in both legs over a period of weeks. Her family report that she has been unsteady and that her speech has been slurred. Her mini mental test score is 21/30. Which one of the following radiological findings is most likely?

A Asymmetrical high signal foci on T2w images in the basal ganglia

B Asymmetrical high signal in the parieto-occipital regions on T2w images with effacement of the occipital horns of the lateral ventricles

C Asymmetrical high signal in the parieto-occipital regions on T2w images with no mass effect

D High T2 signal overlying the left parietal-occipital cortex and causing effacement of the left lateral ventricle and midline shift to the right

E Symmetrical high signal in the periventricular regions on T2w images with further small foci of high signal within the subcortical white matter

Answer 29

C Asymmetrical high signal in the parieto-occipital regions on T2w images with no mass effect

This is progressive multifocal leucoencephalopathy which is seen in 4—5% of patients with AIDS. It is typically parieto-occipital and does not exert mass effect.

Question 30

@# 9. A 36-year-old patient with known AIDS is admitted to your hospital with a right-sided hemiparesis. His wife gives a history of cognitive decline, headache, and lethargy for the past few weeks, but with an acute deterioration in the last 36 hours. His CD4 counts are between 200 and 500 (category B). An MRI is carried out which shows multiple ring-enhancing lesions in the brain. These lesions are high signal on T2WI/FLAIR, but demonstrate a low intensity peripheral ring. Lesions are noted in the basal ganglia bilaterally. The cortical region and subcortical U-fibres are spared. A thallium SPECT is also carried out that shows abnormal uptake in the brain, which correlates with the areas identified on MRI. What is your primary diagnosis?

A. Nocardia abscesses.

B. Toxoplasmosis.

C. Progressive multifocal leukoencephalopathy.

D. Primary CNS lymphoma.

E. Cerebral cryptococcus infection.

Answer 30

9. B. Toxoplasmosis.

This is the most common intracranial opportunistic infection in AIDS patients and the most common cause of intracranial mass lesions in this population, with lymphoma second and cryptococcus third.

Differentiating toxoplasmosis from lymphoma has been the subject of much debate in the literature and ultimately there is no definitive means of differentiating them on imaging alone.

As described toxoplasmosis causes multiple ring-enhancing lesions and often affects the basal ganglia.

Lymphoma tends to involve the subependymal regions and can cause leptomeningeal enhancement. Lymphoma can cause encasement of the ventricle, which is not seen with toxoplasmosis.

Toxoplasmosis tends to be higher intensity on T2WI/FLAIR than lymphoma.

PET and thallium SPECT have also been reported to show abnormal uptake in lymphoma, but not toxoplasmosis, although exceptions exist. Response to anti-toxoplasma treatment is often used as a clinical differentiator.

Cryptococcus classically causes dilatation of Virchow–Robin spaces.

PML is a demyelinating condition secondary to JC virus of oligodendrocytes and is differentiated from other HIV-related demyelinating conditions by affecting the subcortical U fibres.

Question 31

12. A 7-year-old girl is brought into A&E with a history of headache of 4 hours’ duration, associated with neck stiffness. The parents noted a petechial rash and are concerned about the possibility of meningitis. There is no photophobia and no other neurological signs are present. A&E have requested a CT scan to rule out raised intracranial pressure and to diagnose meningitis, whilst also commencing antibiotic therapy for presumed meningitis. The CT scan is normal. As it is a normal working day, A&E have also requested an MRI scan to diagnose meningitis. This was not carried out as the child was agitated. The following day the child develops a pyrexia and a right unilateral aspect to the headache, with decreased GCS. An MRI is carried out and demonstrates features of developing right temporal lobe empyema. Which of the following is an appropriate indication for imaging in the investigation of meningitis?

A. CT to rule out raised intracranial pressure.

B. CT to diagnose meningitis.

C. MRI to diagnose meningitis.

D. MRI due to deterioration in clinical course.

E. All of these.

Answer 31

12. D. MRI due to deterioration in clinical course.

In the absence of clinical features of raised intracranial pressure a CT is not necessarily indicated prior to lumbar puncture to exclude raised intracranial pressure.

CT is also insensitive at diagnosing meningitis, being normal in most uncomplicated cases.

MRI is also negative in 50% of cases of uncomplicated meningitis.

The value of imaging is in the detection of complications of meningitis, including hydrocephalus, abcess, cerebritis, venous thrombosis, and infarction.

Question 32

13. A 13-year-old boy is brought to your paediatric hospital with a recent history of headache and high fever. The child is becoming progressively drowsy and demonstrates rigidity and tremor on neurological examination. An MRI is requested. Relevant past medical history on the request form is of recent travel to Asia, history of measles as a 6-year-old and recent viral infection. The MRI scan shows increased signal on T2WI and FLAIR sequences in the hippocampal regions of the temporal lobes. There is also increased FLAIR signal in the thalami and putamina bilaterally. Small foci of increased T1WI signal within these regions are felt to represent haemorrhage. What diagnosis would you place at the top of your differential list?

A. Herpes simplex type 1 encephalitis.

B. Herpes simplex type 2 encephalitis.

C. Japanese encephalitis.

D. Varicella Zoster encephalitis.

E. Subacute sclerosing panencephalitis (SSPE).

Answer 32

13. C. Japanese encephalitis.

Japanese encephalitis and herpes simplex virus (HSV) encephalitis both present with similar acute and rapidly progressive neurological symptoms.

The key differentiator is involvement of the basal ganglia, which is typical in Japanese encephalitis but rare in HSV.

Both commonly involve the hippocampi, this being the classical appearance of HSV encephalitis.

HSV type 1 is the subtype that affects adult and older children. HSV type 2 causes neonatal and in utero infection.

Herpes varicella zoster virus (VZV) infection can be seen in immunocompromised children, but in the immunocompetent population is more typically seen in elderly patients, often, but not exclusively, in the presence of cutaneous shingles. It causes a vasculitis, which can be seen angiographically and causes bilateral increased T2WI/FLAIR foci and gyriform enhancement in the distribution of the vasculitis.

SSPE presents with a more protracted history of neurological decline.

Question 33

16. An MRI is carried out for your neurology service on a 30-year-old male patient. The most pertinent abnormality is of thick smooth meningeal enhancement following the dural-arachnoid around the convexity, falx, and tentorium without extension into the basal ganglia or ventricles. The referring clinician arrives to discuss the findings, but has mislaid the request form and clinical information. While he is looking for it, what do you think the most likely clinical presentation is?

A. Neck stiffness, photophobia, raised WCC, petechial rash.

B. Neck stiffness, drowsiness, with history of breast cancer.

C. Acute limb weakness on right side 3 days previously, not resolving.

D. Recent back surgery complicated by ongoing CSF leak.

E. Possible fungal meningitis in immunocompromised patient.

Answer 33

16. D. Recent back surgery complicated by ongoing CSF leak.

The key feature is the pattern of meningeal enhancement. It is important to recognize that the imaging findings describe pachymeningeal, not leptomeningeal, enhancement and as such the causes of leptomeningeal enhancement (bacterial or fungal meningitis) can be discounted.

Similarly a recent stroke can cause gyriform enhancement, not pachymeningeal enhancement.

Breast cancer is the most common malignancy to cause pachymeningeal enhancement, but this would usually be more nodular than smooth.

CSF leak or any cause of intracranial hypotension will be associated with smooth pachymeningeal thickening, primarily over the convexities and falx. This enhances, not because of any inflammatory process, but because this part of the meninges has no blood–brain barrier, unlike the leptomeninges.

Question 34

(Ped) 2 A six-year-old girl presents with a three-day history of irritability, headache and high fever. On examination she is lethargic and pyrexial with no evidence of a purpuric rash. The paediatricians suspect that the patient has herpes encephalitis. An MRI brain is performed. What imaging findings are most likely to be seen?

a Nothing, it is too early

b Temporal lobe high signal on T2-weighted images; low signal on T1-weighted images

c Periventricular high intensity on T1-weighted images

d Temporal lobe low signal on T2-weighted images; low signal on T1-weighted images

e Hyperintense signal in the brain stem

Answer 34

2 Answer B: Temporal lobe high signal on T2-weighted images, low signal on T1-weighted images

Herpes simplex encephalitis most commonly affects the temporal lobe with a propensity for the limbic system.

A CT may be negative for three days but the MRI should be positive within two days.

The signal increases on diffusion weighting, as it is cytotoxic oedema.

Small focal haemorrhages are common.

Question 35

(Ped) 25 An eight-month-old child presents with a rapid onset of lethargy and irritability. The child is hard to examine due to excessive crying. The child has a fever and diarrhoea but no purpuric rash. The paediatricians diagnose meningitis on a lumbar puncture. A week later the child is still septic, lethargic and is now showing signs of raised intracranial pressure. An enhanced CT brain is performed showing a hypodense lentiform zone with ring enhancement adjacent to the skull in the right parieto-temporal region. What complication is present?

a Subdural haematoma

b Extradural haematoma

C Cerebral aneurysm

d Epidural abscess

e Subdural empyema

Answer 35

25 Answer E: Subdural empyema

The patient has bacterial meningitis that is complicated with a subdural empyema. There are many potential complications of bacterial meningitis including subdural effusions (which may become secondarily infected becoming subdural empyemas), cerebritis & ventriculitis, atrophy, infarction, hydrocephalus & cranial nerve dysfunction.

Question 36

44 Regarding Cryptococcus neoformans in H.immunodeficiency virus. Which of following statements is correct?

a Cryptococcus neoformans is the most common fungal infection in AIDS

b It is found in bird excrement and spreads by direct invasion

C Results in abscess formation in the basal ganglion

d Results in a florid meningitic response

e Results in effacement of the perivascular spaces

Answer 36

44 Answer A: Cryptococcus neoformans is the most common fungal infection in AIDS

Cryptococcus neoformans is the most common fungal CNS infection in AIDS and is the third most common CNS pathogen after toxoplasmosis and HIV.

It is inhaled from bird excrement and spread haematogenously to the brain.

It typically results in meningitis, which is poorly appreciated on imaging as the pathogen does not exhibit a strong inflammatory response.

A gelatinous mucoid material is produced, which results in widening of the subarachnoid spaces.

Cryptococcomas are another feature of Cryptococcus infections. They present as small non-enhancing low-density lesions within the basal ganglia with variable enhancement. These lesions represent dilated perivascular spaces filled with gelatinous cryptococcomas. MRI has a greater sensitivity for the detection of cryptococcomas.

Question 37

(Ped) 44 A girl who was born with Tetralogy of Fallot presented to the Emergency Department with fever and drowsiness. A CT scan was performed, which showed a ring-enhancing low-density lesion with surrounding oedema within the frontal lobe. What is the most likely diagnosis?

a Astrocytoma

b Metastasis

c Lymphoma

d Frontal lobe abscess

e Craniopharyngioma

Answer 37

44 Answer D: Frontal lobe abscess

Causes of brain abscesses include:
* extension from paranasal sinus infection
* septicaemia originating in the lung (e.g. bronchiectasis)
* septicaemia originating in the heart (e.g. congenital heart disease with right to left shunt, bacterial endocarditis)
* septicaemia originating with osteomyelitis
* penetrating trauma or surgery
* cryptogenic.

Question 38

45 Regarding tuberculosis in the HIV population. Which of the following statements is correct?

a Tuberculosis abscess are the most common presentation

b Typically results from direct spread from adjacent structures

c Tuberculomas occur in the posterior fossa

d The typical imaging feature of a tuberculoma is a target lesion

e Hydrocephalus is typically obstructive in nature

Answer 38

45 Answer D: The typical imaging feature of a tuberculoma is a target lesion

CNS tuberculosis has increased in the developed world secondary to the increasing incidence of AIDS. It is typically spread haematogenously from a pulmonary source and most commonly presents as meningitis. On cross-sectional imaging there is thick enhancement of the meninges and ependyma. Communicating hydrocephalus is common due to reduced resorption of CSE Tuberculomas typically arise in the corticomedullary region and are supratentorial. They commonly appear as target lesions on both CT and MRI.

Question 39

@# (Ped) 25 You are asked to perform a cranial ultrasound scan on a neonate who was born with poor APGAR scores and made a poor inspiratory effort. On the ultrasound you find multiple irregular foci of calcification throughout the periventricular region, the thalamus and basal ganglia. What is the most likely diagnosis?

a Congenital Cytornegalovirus infection

b Tuberous sclerosis

c Congenital toxoplasmosis infection

d Grade IV acute haemorrhage

e Periventricular leukomalacia due to hypoxic injury

Answer 39

25 Answer C. Congenital toxoplasmosis infection

The presentation of congenital toxoplasmosis infection is very non-specific, as with most of the congenital infections.

The ultrasound characteristics are different from congenital Cytornegalovirus in that the calcifications are in the basal ganglia and thalamus as well as the periventricular region.

The calcifications can be lobulated or curvilinear and can be present in the choroid plexus.

The location also differentiates the findings from tuberous sclerosis.

Periventricular leukomalacia findings are a broad zone of periventricular echogenicity.

Question 40

44 A 40-year-old man with headaches was assessed with a CT which showed a thin-walled uniformly enhancing lesion with marked vasogenic oedema in the right temporal lobe adjacent to the petrous ridge. On MRI the lesion appeared iso-hypointense on Ti and hyperintense on T2- weighted images. On DWI there was high signal and low signal on the ADC map. What is the most likely diagnosis?

a Glioblastoma multiforme

b Cerebral abscess

c Arachnoid cyst

d Metastasis

e Chronic haematoma

Answer 40

44 Answer B: Cerebral abscess

Cerebral abscesses typically result in a thin uniformly enhancing rim of contrast while metastasis and GBM have thick walls and incomplete enhancement. The DWI characteristics are of restrictive diffusion, which occur in infarcts and cerebral abscesses, although not all abscesses demonstrate these signal characteristics. Sometimes the abscess may have a thin rim of high signal on Ti and low signal on T2-weighted imaging, which is caused by haemorrhage or free radicals.

Question 41

43 A 42-year-old woman with a proceeding history of flu-like symptoms presented with a day history of increasing confusion followed by three generalised seizures. Initial CT revealed no abnormality while an MRI showed high signal on T2 in the medial right temporal and right insula region. No enhancement with gadolinium and little mass effect were seen. She remained in intensive care and a repeat MRI a week later showed extensive high signal in the temporal lobes and frontal lobes with multiple low-signal foci on T2 GRE. There was no ventricular dilatation. What is the most likely diagnosis?

a Toxoplasmosis

b Herpes encephalitis

C Low-grade glioma

d Paraneoplastic syndrome

e Cytornegalovirus infection

Answer 41

43 Answer B: Herpes encephalitis

Herpes simplex encephalitis results in fulminant necrotising encephalitis and is due to the herpes simplex virus (HSV).

A third of patients have a primary infection while the rest are due to reactivation.

Patients present with acute confusion and disorientation which can progress to fits, loss of consciousness and death. HSV has a predilection for the temporal lobes, insula, frontal lobes and cingulated gyrus. The putamen is typically spared. On early imaging on FLAIR and T2W there is high signal in these areas. There may be restricted diffusion in the affected areas due to infarction and lack of restrictive diffusion suggests reversibility.

At 10 days the extent of the tissue involved is known, and parenchymal haemorrhage can be seen at this stage.

The prognosis is poor with only 2.5 % of treated HSV patients returning to a normal life. If untreated there is a 70% mortality.

Question 42

65 Regarding Cytornegalovirus (CMV) in human immunodeficiency virus, which of the following statements is correct?

a CMV infections are the result of primary infection

b CMV infections most commonly affect the nervous system

C It rarely occurs with other opportunistic infections

d CMV infections can cause a brachial plexus neuropathy

e Causes periventricular calcification

Answer 42

65 Answer D: CMV infections can cause a brachial plexus neuropathy

CMV in the AIDS population is usually the result of reactivation.

Ninety per cent of the general population have prior exposure to CMV, usually in childhood.

CMV infection more typically affects the respiratory tract. Fifteen to thirty per cent of HIV patients have CNS evidence of the virus at post mortem. Brain involvement results in encephalitis, ventriculitis, infarcts or meningitis.

On CT imaging there is low density diffuse white matter changes, ependymal enhancement and ringenhancing lesions.

CMV infections not uncommonly arise with other opportunistic infections such as toxoplasmosis and cryptococcosis.

Diffuse periventricular calcification occurs in the congenital form and is not a feature of CMV infection in HIV

Question 43

45 A 46-year-old HIV-positive female with a CD4 count of 40cells/cumm was admitted with a month’s history of progressive confusion. A MRI was performed which demonstrated bilateral, asymmetrical patchy white matter changes with no mass effect or enhancement. What is the most likely diagnosis?

a Progressive multifocal leukoencephalopathy

b Toxoplasmosis

C Lymphoma

d HIV encephalopathy

e CMV

Answer 43

45 Answer A: Progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy is caused byJC virus and results in destruction of the oligodendrocytes, resulting in demyelination.

It affects the white matter anywhere in the brain in HIV patients and is often bilateral but asymmetrical and is not associated with atrophy. Death typically occurs within six months. The white matter lesions do not exhibit mass effect and show minimal enhancement.

Lymphoma and toxoplasmosis are more commonly discrete ring enhancing lesions.

CMV typically results in patchy diffuse periventricular white matter changes.

Human immunodeficiency virus produces a subacute encephalitis, which is characterised by progressive dementia.

Question 44

@# 46 A 2 7-year-old HIV positive man was admitted with increasing confusion and lethargy. He had a CD4 count of 150 but had no history of an AIDS-defining illness. Cross-sectional imaging of the head was performed. What features make a diagnosis of toxoplasmosis more likely than lymphoma?

a Corpus callosum involved

b Haemorrhage on CT

C Basal ganglia lesions

d Single lesion

e Subependymal spread

Answer 44

46 Answer B: Haemorrhage on CT

Differentiating toxoplasmosis and cerebral lymphoma can be difficult as both can present as multiple ring enhancing lesions.

Features that are more likely to represent lymphoma are a single lesions, subependymal spread and lesions within the corpus callosum.

Features that are more likely to represent toxoplasmosis are haemorrhage on CT and high signal on T2 W imaging.

Toxoplasmosis has a predilection for the basal ganglia but lymphoma can also be found in this region.

Question 45

56 You are called to perform a cranial ultrasound on a neonate who has been critically ill after birth with low APGAR scores. The baby has not progressed as expected and is lethargic and less responsive than hoped. On the ultrasound, in the coronal view, a line of hyper-reflective dots is seen under the lateral ventricles. Which of the following is the most likely diagnosis?

a Tuberous sclerosis

b Congenital toxoplasmosis infection

C Periventricular infarcts

d Rubella

e Congenital Cytomegalovirus infection

Answer 45

56 Answer E: Congenital Cytornegalovirus infection

Cytornegalovirus infection affects up to 1 % of pregnancies but symptoms only occur in less than 10% of those infected. There are multiple manifestations including IUGR, hepatosplenomegaly, jaundice, pneumonitis, microcephaly and chorioretinitis. Long-term neurodevelopmental sequelae are common.

Typical findings on cranial ultrasound are periventricular subependymal cysts, periventricular calcifications and hydrocephalus.

Cytornegalovirus tends to cause periventricular calcification while toxoplasmosis causes widespread calcifications. Periventricular infarcts will not be so well defined.

Tuberous sclerosis can cause subependymal hamartomas, which calcify with age, and cortical or subcortical tubers, which produce curvilinear calcifications.

Rubella is much less common than congenital CMV infection.

Question 46

@# 70 A 27-year-old female with AIDS presented with a fit and following further investigations, including CT and MRI scans, her symptoms were felt to be attributable to HIV encephalitis. Which region of her brain is most likely to be abnormal on the MRI scan?

a Anteroinferior aspects of the temporal lobes

b White matter of the centrum semiovale

C Corpus striatum (putamen and caudate nuclei)

d Superior cerebellar peduncles

e Hypothalamus

Answer 46

70 Answer B: White matter of the centrum semiovale

Human immunodeficiency virus causes encephalitis in 60% of patients with AIDS.

It predominately affects the white matter, particularly the centrum semiovale and results in gliosis and demyelinating plaques.

These plaques are not dissimilar to plaques in multiple sclerosis as they are in a periventricular position and high signal on T2-weighted images. Unlike plaques in MS they tend not to enhance with contrast. (Acute plaques in MS can enhance for up to six weeks after they first appear.)

Generalised diffuse parenchymal atrophy is a feature.

Question 47

(Ped) 21. A new born child presents with failure to thrive. Cranial ultrasound shows multiple echogenic foci in a periventricular distribution. There is no hydrocephalus and no evidence of callosal agenesis. CT scan shows extensive calcifications in the subependymal region. The most likely diagnosis is?

(a) Hydrocephalus

(b) Periventricular leukomalacia

(c) Periventricular calcifications

(d) Germinal matrix calcifications

(e) Congenital cytomegalovirus infection

Answer 47

21. (e) Cytomegalovirus infection

Intracranial calcifications are seen in congenital TORCH infections, tuberous sclerosis, Sturge-Weber syndrome, bacterial meningitis with ventriculitis and teratoma.

Cytomegalovirus infection is the most common TORCH infection.

Periventricular and subependymal calcifications are common manifestation of cytomegalovirus infection.

Calcifications in cytomegalovirus tend to be limited to the subependymal region, while in toxoplasmosis they are seen throughout the parenchyma.

Calcifications are much less in herpes simplex and rubella.

In tuberous sclerosis, calcifications are likely to be seen in adolescence.

Question 48

26. A 20-year-old immigrant from South America presents with seizure. CT of the brain shows multiple cystic lesions, with some of them showing calcification. On MRI, there are multiple fluid-containing cysts in the brain, some of which contain small nodules. There is mild surrounding oedema. The most likely diagnosis is?

(a) Multiple brain abscesses

(b) Neurocysticercosis

(c) Tuberculomas

(d) Metastases

(e) Sarcoidosis

Answer 48

26. (b) Neurocysticercosis

This is the most common parasitic infection of the brain and is particularly prevalent in South America, Asia and Africa. In the vesicular stage, CT and MRI show multiple, thin-walled cysts containing scolex with minimal surrounding oedema.

Question 49

10. Characteristic features of Herpes simplex encephalitis (HSE) in adults include: (T/F)

(a) Unilateral cerebral involvement

(b) Infection by HSV type II

(c) Untreated infection has a mortality rate of 50-70 %

(d) Gyriform enhancement on contrast enhanced CT

(e) High signal in the cingulated gyrus on T2W MRI.

Answer 49

Answers:

(a) Not correct
(b) Not correct
(c) Correct
(d) Correct
(e) Correct

Explanation:
Neonatal herpes is caused by HSV II and herpes in adults is caused by HSV I. In adults, herpes initiates as unilateral involvement of limbic system ( temporal bones, insular cortex, subfrontal area and cingulated gyri) but eventually follows bilaterally. CT performed early in the course of illness may be normal or only subtly normal.

Question 50

12. Which of the following statements are correct about Pyogenic brain abscesses: (T/F)

(a) Most commonly occur secondary to a generalised septicaemia.

(b) Typically occur at the corticomedullary junction.

(c) On CT have a smooth regular wall with relative thinning of the lateral wall.

(d) Are more common in the occipital lobes than the frontal lobes.

(e) The most common causative organism is Staphylococcus.

Answer 50

Answers:

(a) Not correct
(b) Correct
(c) Not correct
(d) Not correct
(e) Not correct

Explanation:
32% of the pyogenic brain abscesses could be due to generalised septicaemia for example, from a lung abscess or pneumonia. However 41% occur secondary to extension from paranasal sinus infection.

The occur most commonly in the frontal lobes than in the occipital lobes.

On CT there is a relative thinning of the medial wall due to would blood supply of white matter which leads to the rupture of the abscess into the ventricular system.

Most common causative organism is streptococcus.

Question 51

19. Concerning differences between primary CNS lymphoma and toxoplasmosis: (T/F)

(a) Subependymal extension across the corpus callosum is more likely to occur in toxoplasmosis.

(b) High signal on T2 weighted MRI favours lymphoma.

(c) Toxoplasmosis is more frequently multiple.

(d) Ring enhancement following contrast administration favours lymphoma.

(e) The lesions are usually smaller in lymphoma.

Answer 51

Answers:

(a) Not correct
(b) Not correct
(c) Correct
(d) Not correct
(e) Not correct

Explanation:
CNS lymphoma shows subependymal extension across the corpus callosum.

CNS lymphoma and toxoplasmosis lesions can be smaller as well as large and should not be differentiated on basis of size.

Toxoplasmosis shows high signal on T2-weighted MRI and shows ring enhancement on post contrast images.