Posterior fossa neoplasms in children are usually due to either medulloblastoma, ependymoma, pilocytic astrocytoma or brain stem glioma. 

Clues to the specific diagnosis include cystic neoplasm with enhancing nodule in pilocytic astrocytoma and inhomogeneous mass more often with calcification and extrusion into foramen with ependymoma.

 Unfortunately, the diagnosis must still be made histologically as many tumors do not adhere to such criteria. 

Medulloblastoma usually presents with headache, emesis and lethargy as patient is usually hydrocephalic at time of diagnosis.

 Occasionally, patient has symptoms of brainstem compression such as head tilt, hearing loss or facial weakness. 

 Medulloblastoma has an increased association:

Turcot’s syndrome

Ataxia-telangectasia

Gorlin syndrome (autosomal dominant basal cell nevus syndrome)Gardner syndrome

Cowden syndrome

Taybi and Coffin-Siris syndrome. 

Imaging usually shows a fairly homogeneous mass due to the homogeneous nature of the lesion histologically. It may therefore be hyperdense (90%) on noncontrast CT.  

Metastases are direct extension through the subarachnoid space in the ventricular system, basal cisterns and thecal sac and are imaged with post contrast MRI.

 Calcification, cystic change, necrosis or hemorrhage in less than 15% of patients. 

MR Spectroscopy shows $$ NAA and ##increased Choline and lactate usually present. 

More than 50% of patients are disease free at 5 years with complete resection, more than 80% if no metastases are present at presentation. 

MNEMONIC FOR POSTERIOR FOSSA TUMORS IN CHILDREN: 

GAME

G-Brian stem glioma

A-Pilocytic astrocytoma

M- Medulloblastoma

E- Ependymoma

  Multiple PNET and rhabdoid tumors can also occur in the posterior fossa. 

Differential Diagnosis of DROP METS IN CHILDREN:

Medulloblastoma

Ependymoma

Hypothalamic astrocytoma

Thalamic glioma

Choroid plexus carcinoma

Pineal tumors

Lymphoma, Leukemia 

Take Home Message:

Rhabdoid tumors of the kidney are associated with posterior fossa brain tumors. 

Medulloblastoma arises from the roof ( superior medullary velum) of fourth ventricle. 

Ependymoma arises from the floor of the fourth ventricle