Posterior Cranial Fossa Lesions Flashcards
What are the ddx for PCF masses in children?
- Medulloblastoma
- Juvenile Pilocytic Astrocytoma (JPA)
- Ependymoma
- Brainstem glioma
- Atypical teratoid rhabdoid tumor (ATRT)
What are the ddx for PCF masses in adults?
- Infarcts
- Metastatic disease
- Hemangioblastoma
- Vascular malformation
- Hypertensive haemorrhage
Imaging features for medulloblastoma (paediatric PCF masses)
- Most common posterior fossa tumor in children
- it is a primitive neuroectodermal tumor (PNET)
- Peak incidence is within first decade of life. Fast growing, over weeks.
- LOCATION: The tumor typically arises from the superior medullary
velum or roof of fourth ventricle. Although characteristically
midline, lateral (cerebellar hemisphere) origin may be seen in older children and young adults. - MORPHOLOGY: Lesions are hyperdense on CT, cysts/necrosis is common, calcification seen in 10-20%
MRI: restricted diffusion due to high cellular content. T1 hypointense and T2 iso- to hyperintense with heterogeneous enhancement. Cystic changes occur in half of the cases; calcification occurs in approximately 20%. Subarachnoid seeding is noted in up to one-third of the cases at presentation; therefore, evaluation of the neuroaxis is
required prior to surgical resection.
Imaging features of ATRT (paediatric PCF masses)
- Rare, aggressive embryonal tumor composed of rhabdoid cells and
PNET components. - Seen in VERY YOUNG CHILDREN, first few years of life.
- LOCATION: most located in the posterior fossa and the remainder occurring supratentorially.
- MORPHOLOGY: aggressive appearance. gross examination and imaging is nearly identical to medulloblastoma.
- Subarachnoid seeding
is common. - Prognosis is dismal; mean survival is less than
6 months if younger than 3 years at the time of presentation.
Imaging features of Juvenile Pilocytic Astrocytoma (JPA) (paediatric PCF masses)
- second most common primary posterior
fossa tumor in children with an incidence slightly below medulloblastoma. - They may be sporadic or associated with NF1.
- Peak incidence is 5 to 15 years of age.
- LOCATION: The tumor arises from the cerebellar hemisphere; therefore, it is typically off-midline.
- MORPHOLOGY: The most common presentation is a cystic mass with an
enhancing mural nodule. The cystic component is T1 iso- to
hypointense and T2/FLAIR hyperintense. The solid component is T2 and FLAIR hyperintense and enhances avidly. Enhancement
of the cyst wall suggests the presence of tumor cells.
- A less common imaging appearance includes a solid mass with a cystic/necrotic center.
What syndromes are associated with medulloblastoma?
Coffin-Siris syndrome
Cowden syndrome
Gardner syndrome
Gorlin syndrome
Li-Fraumeni syndrome
Rubinstein-Taybi syndrome
Turcot syndrome
L-2-hydroxyglutaric aciduria
Imaging features of ependymoma (TOOTHPASTE TUMOR) (paediatric PCF masses)
- LOCATION: Slow-growing, midline posterior fossa tumor. Two-third of them originate along the floor of the fourth ventricle. It characteristically squeezes through the fourth ventricle foramina into the foramen magnum, cerebellopontine
angle, or cisterna magna. One-third of the cases are supratentorial and centered in the brain parenchyma. - Mean age of presentation is 6 years of age.
- MORPHOLOGY: On CT, calcification is seen in approximately 50% of cases;
cystic change and hemorrhage occur in approximately 20%.
- MRI: iso- to hypointense on T1 and hyperintense
on T2 sequences. There is mild to moderate heterogeneous enhancement
of solid components. CSF dissemination occurs but
is less common than with medulloblastoma.
Imaging feature of PCF infarction (adult PCF “mass”)
- Ischemic changes commonly affect the posterior fossa and may have a masslike appearance.
- MORPHOLOGY: wedge-shaped area, corresponding to a vascular territory (posterior inferior, anterior inferior, and superior
cerebellar arteries). Other differentiating features include restricted
diffusion in the acute and early subacute stages and
occasionally vascular occlusion demonstrated on CTA or MRA. Edema, mass effect, hemorrhagic transformation, and subacute enhancement may mimic a mass.
Imaging features of metastatic disease (PCF Masses in adults)
- Metastatic disease represents the most
common posterior fossa parenchymal neoplasm in middle-aged and older adults. Lung, breast, and gastrointestinal
malignancies are among the most common. - More often multiple.
- MORPHOLOGY: Tumors are typically solid; cystic change and calcification
occasionally occur with mucinous adenocarcinomas.
Hemorrhagic metastases, which may occur with breast, lung, renal cell, thyroid, melanoma, and choriocarcinoma, tend to
have strong enhancement and a hemosiderin rim. Renal cell carcinoma metastases may mimic hemangioblastoma, as they
are very vascular.
Imaging features of hemangioblastoma (PCF mass in adult)
- Hemangioblastomas are lowgrade (WHO grade I) meningeal neoplasms and are the most common primary posterior fossa neoplasms in adults.
- LOCATION: 90-95% occur within the posterior fossa, typically within the
cerebellar hemispheres, while 5 to 10% are supratentorial. Supratentorial
lesions commonly occur in the setting of von Hippel
Lindau (VHL) disease. - MORPHOLOGY: Larger lesions present as cystic masses with enhancing mural nodules (similar to juvenile pilocytic astrocytoma) which
abut the pial surface; smaller lesions commonly present as
solid enhancing masses. The cyst and nodule are T2 hyperintense.
Solid components avidly enhance, abut the pial surface, and may demonstrate flow voids. - When identified, the entire
neuroaxis should be imaged to look for additional cord lesions.
Approximately one-fourth to one-half of patients with posterior fossa hemangioblastomas will have VHL. Patients with
VHL may also have retinal hemangioblastomas, endolymphatic
sac tumors, renal cell carcinoma, pheochromocytoma, islet
cell tumors, and visceral cysts.
Imaging features of vascular malformations in the posterior cranial fossa.
Arteriovenous malformations
(AVMs) consist of a nidus of abnormal connections between
arteries and veins without intervening capillaries.
CT may demonstrate regions of increased density or calcification.
MRI reveals a tangle of enlarged vessels; perinidal aneurysms are a common source of hemorrhage.
Cavernous malformations
(CMs) consist of blood-filled sinusoids and cavernous
spaces without intervening parenchyma. CT may be normal or show subtle regions of calcification or hemorrhage. Lesions
have foci of increased and decreased T1 and T2 signal centrally with a T2 dark (hemosiderin) capsule on MRI.
Imaging features of hypertensive haemorrhage in posterior cranial fossa.
Hypertensive hemorrhage commonly involves the posterior fossa, to include the pons and cerebellar hemispheres.
Hemorrhagic foci are typically round or oval. Acute hemorrhage is hyperdense on CT with mass effect
and surrounding edema.
MR appearance varies based on the age of blood products and composition of the hemoglobin moiety.
Gradient echo and susceptibility weighted imaging often identify additional foci of microhemorrhage associated
with hypertension in the lentiform nuclei and thalami.
Chiari malformations are a group of defects associated with congenital caudal displacement of the cerebellum and brainstem.
What is Chiari I?
most common type of Chiari malformation (Type 1 to 5). Normal size posterior fossa.
peg-like cerebellar tonsils displaced into the upper cervical canal through the foramen magnum >=5mm. Can have syrinx.
Chiari malformations are a group of defects associated with congenital caudal displacement of the cerebellum and brainstem.
What is Chiari II?
Small posterior fossa is a
hallmark of Chiari type II.
displacement of the medulla, fourth ventricle, and cerebellar vermis through the foramen magnum
usually associated with a lumbosacral spinal myelomeningocele
What is the Dandy-Walker malformation (DWM)?
The most common posterior fossa malformation, characterised by the triad of:
1) hypoplasia of the vermis and cephalad rotation of the vermian remnant
2) cystic dilatation of the fourth ventricle extending posteriorly
3) enlarged posterior fossa with torcular-lambdoid inversion (the confluences of the sinuses, the torcula, lying above the level of the lambdoid sutures due to abnormally high tentorium)
Sagittal image shows a large posterior fossa cyst elevating the tentorium and sinus rectus (red arrow). The hypoplastic vermis is everted over the posterior fossa cyst (yellow arrow). The cerebellar hemispheres and brainstem are hypoplastic (green arrow). Thinned occipital squama is seen (blue arrow).
Axial image shows hydrocephalus, a large cerebrospinal fluid cyst in the posterior fossa and hypoplastic cerebellar hemispheres with a winged appearance (white arrowheads).
Features of intracranial hypotension (to look for when the findings is “sagging” of the brain and inferior tonsillar displacement)
SEEPS
- Etiologies include iatrogenia (postsurgical or procedural, such as lumbar puncture), trauma, violent coughing or strenuous exercise, spontaneous dural tear, ruptured arachnoid diverticulum, severe dehydration, and, rarely, calcified disc protrusion with dural injury.
S: subdural fluid collections
E: enhancement of the pachymeninges (Diffuse thickened, FLAIR hyperintense, enhancing dura)
E: engorgement of the venous sinuses (rounded prominent appearance, venous distension sign)
P: pituitary enlargement/ hyperaemia
S: sagging brain
- Radionuclide cisternography
or computed tomography myelography can be used to
search for the site of cerebrospinal fluid (CSF) leak if blood
patch therapy fails.
