Ch15 Intracranial anomalies Flashcards
What are the most common locations for arachnoid cysts?
Middle fossa (50% in the sylvian fissure), CPA (10%), suprasellar (10%) and posterior fossa (10%).
What are the imaging features of an arachnoid cyst?
Follows CSF on call sequences and associated with remodelling of the bone.
How do you manage an incidental arachnoid cyst?
MRI+C and single further f/u study in 6 months to rule out increase in size.
What is the aetiology of an arachnoid cyst?
Developmental splitting of the arachnoid membrane. Histologically are lined by meningothelial cells and are positive for EMA.
What is the incidence of arachnoid cysts?
5 per 1000 at autopsy
What condition are bilateral arachnoid cysts associated with?
Hurler’s syndrome (mucopolysaccaridosis)
What is the main differential diagnosis of an arachnoid cyst?
Epidermoid (shows restricted diffusion) Porencephalic cyst (lined by WM) Schizencephaly (lined by heterotopic GM)
How do suprasellar arachnoid cysts present?
Endocrinopathy Developmental delay Hydrocephalus Visual loss Precocious puberty Bobble-head doll syndrome
What is the classification for arachnoid cysts?
Galassi classification 1 - temporal pole and communicates with subarachnoid space during cisternography. 2 - anterior 1/2 of sylvian fissure with partial communication with subarachnoid space. 3 - Involves entire sylvian fissure and shows no communication with subarachnoid space.
What are the treatment options for arachnoid cysts?
- needle aspiration / burr hole drainage (high recurrence rate) 2. Craniotomy, excision of cyst wall and fenestration into basal cisterns (higher morbidity and may need a VP shunt) 3. Endoscopic fenestration 4. Cyst shunting into the peritoneum (become shunt dependent)
What valve should be used if shunting an arachnoid cyst?
Low pressure
What are the surgical approaches for drainage of a suprasellar arachnoid cyst?
Transcallosal transventricular and transcortical transventricular
When do the fontanelles close?
Anterior fontanelle 2-3 years Mastoid fontanelle - 1 year Posterior fontanelle 2-3 months Sphenoid fontanelle 6 months
When is 90% of adult head size achieved?
1 year. Full size by age 7.
When do mastoid air cells form?
6 years
What is primary craniosynostosis?
Prenatal deformity caused by suture fusion
What is secondary craniosynostosis?
Metabolic (Rickets), Drugs (AEDs), Haemotological (Sickle cell / thalassemia) and structural (microcephaly)
What are the surgical indications for multi-suture craniosynostosis?
Impedes brain growth and for raised ICP. Note 10% of single suture craniosynostosis also develop raised ICP.
Which craniosynostosis may result in amblyopia?
Coronal
What do you feel when palpating a craniosynostosis?
Ridge (except lambdoid which may be a trough)
What does metopic synostosis cause?
Trigonocephaly
What does single coronal suture synostosis cause?
Anterior plagiocephaly
What does bilateral coronal suture synostosis cause?
Brachycephaly
What does sagittal suture synostosis cause?
Scaphocephaly
How do you differentiate positional plagiocephaly from unilateral lamboid suture synostosis?
Position of the ear is pulled back with unilateral lamboid suture synostosis and the skull forms a trapezoid shape compared to a parallelogram that is seen with positional plagiocephaly
What is the most common single suture synostosis?
Scaphocephaly (sagittal suture synostosis) - 80% occur in males
How is Scaphocephaly (sagittal suture synostosis) treated?
Strip craniectomy with excision of the sagittal suture
How can Crouzon’s and Apert’s syndromes be distinguished?
Both cause coronal suture synostosis which is more common in females. Crouzon’s is associated with midface hypoplasia whilst Apert’s is associated with syndactyly.
What eye sign is seen with unilateral coronal suture synostosis?
Harlequin eye sign
How is coronal suture synostosis treated?
Suturectomy or frontal craniotomy with orbital advancement
What chromosome abnormality is associated with metopic synostosis?
Ch19q
What investigations may be performed for synostosis?
Xray, CT and Tc bone scans
What is the management of positional plagiocephaly?
Repositioning therapies Surgery in 20% of cases that are refractory to repositioning therapies There is no evidence for helmets but some use them
What mutation is found with Crouzon’s and Apert’s?
FGFR (autosomal dominant)
What is the cause of a polypoid mass in the nose of an newborn?
Encephaloceole
How are encephalocoeles classified?
Suwanwela and Sunwanela classification into: Occipital, cranial vault, frontoethmoidal, basal and posterior fossa.
What % of infants with encephaloceles develop normally?
<5%. The more neural tissue the worse the outcome.
What is Dandy Walker malformation?
An enlarged posterior fossa with cerebellar hypoplasia / agenesis and cystic dilatation of the 4th ventricle (also has an enlarged cisterna magna).
What is a Dandy Walker variant?
When not all 3 factors for Dandy walker malformation are present e.g. posterior fossa may not be enlarged but there is dilatation of the 4th ventricle and vermian agenesis for example.
What is a persistent blake’s pouch cyst?
Blake’s pouch is a transient protrusion from the 4th ventricle through the foramen of magendie that usually regresses by 4 months gestation. The torcula is in the correct place. If persistent results in an imperforate foramen of magendie.
What is the differential for a posterior fossa cyst?
Dandy-walker malformation
Dandy-walker variant
Persistent blake’s pouch cyst
Arachnoid cyst
Mega cisterna magna
Joubert’s syndrome due to underdevelopment of the vermis
How can Dandy Walker malformation be distinguished from other posterior fossa cysts?
DWM has true vermian agenesis. The others just compress the vermis.
Choroid plexus is absent
What is PHACES syndrome?
Posterior fossa malformation
Haemangioma (craniofacial)
Arterial anomalies of the head and neck
Coarctation of the aorta / cardiac defects
Eye anomalies
Sternal cleft
What syndrome can Dandy walker malformations be associated with?
PHACES
What is the treatment for Dandy Walker Malformation?
Treatment of hydrocephalus through shunting of the posterior fossa cyst afte ruling out aqueductal stenosis
(not the lateral ventricles due to risk of upward herniation)
ETV can also be performed
What conditions are associated with aqueductal stenosis?
Chiari malformation and neurofibromatosis
What visual abnormalities are associated with papilloedema?
Visual obscurations and lack of acuity
Peripheral field cuts
Increased blind spot
Why is contrast given when investigating aqueductal stenosis?
To rule out tumour
What are the treatments for Aqueductal stenosis?
- ETV
- VP shunt
- Tokildsen shunt (lateral ventricle to cisterna magna)
What causes callosal agenesis?
Failure of commissuration of the prosencephalon which occurs ~8 weeks gestation.
What is indicated by absence of the anterior CC but presence of the posterior CC?
Holoprosencephaly
What is Aicardi syndrome?
Agenesis of the CC
Seizures
Retardation
Retinal pigmentation
What conditions are associated with absence of the septum pellucidum?
Holoprosencephaly
Schizencephaly
Agenesis of the CC
CM type 2
Septo-optic dysplasia
Chronic hydrocephalus
Where are intracranial lipomas most commonly found?
Corpus callosum (associated with callosal agenesis)
What is the differential diagnosis of an intracranial lipoma?
Dermoid cyst, teratoma and germioma
What is the difference between a dermoid and a teratoma?
Dermoids are ectodermal in origin (predominantly skin and hair)
Teratomas are mesoderm and endoderm (predominantly fat, muscle and bone).
Where do hypothalamic hamartomas arise from?
The tuber cinereum
What are sessile hypothalamic hamartomas?
Remain within the hypothalamus (oppose to pedunculated ones which are parahypothalamic)
How to Hypothalamic Harmatomas present?
Precocious puberty, gelastic seziures and developmental delay
How are Hypothalamic Hamartomas treated?
GnRH analogues for precocious puberty
For pedunculated HH, open approaches through pterional craniotomy or LITT
What syndrome is associated with HH?
Pallister-Hall syndrome
What are the imaging features of HH?
Iso on T1 and T2 with no contrast enhancement
Lesion arising from the floor of the third ventricle
