Teaching Case

Worsening occipital headaches, vomiting and visual disturbance.

This patient presented with a four-week history of occipital headaches, occasional vomiting and diplopia – worse on the right. Her symptoms progressed and prompted urgent admission. Clinical examination revealed a right 6th cranial nerve palsy and bilateral papilloedema. An urgent MRI scan of the brain was performed to investigate suspected intracranial pathology. Pre and post gadolinium enhanced T1 and T2 weighted images were acquired. These showed a large heterogeneous posterior fossa mass with areas of signal void secondary to both calcification and vessels. The lateral and third ventricles were dilated with associated periventricular oedema representing acute non-communicating obstructive hydrocephalus. The mass showed mixed enhancement with gadolinium. No spinal abnormality was identified.

Medulloblastoma accounts for 15-20% of all paediatric intracranial tumours and is the most common posterior fossa malignancy of childhood comprising 30-40% of cases. 75% will classically arise in a midline infratentorial position from cells of the inferior medullary velum of the cerebellar vermis, which forms the roof of the fourth ventricle. Medulloblastomas are histologically primitive neuroepithelial cells and are predominantly undifferentiated but may take a neuroblastic form or show either glial cell or mucosal gland differentiation. They are part of the primitive neuroectodermal group of tumours (PNETs).
Ninety percent of medulloblastomas will cause hydrocephalus and raised intracranial pressure as they efface the fourth ventricle and aqueduct of Sylvius. Local CNS dissemination along CSF pathways is common (50-60%) with spinal “drop metastases” occurring in 40% of cases. Non CNS metastases (6%) arise in the pelvis, long bones, spine, lymph nodes and lung.
There is a male predominance (3:1) with 75% occurring in the 1st decade and 40% presenting by 5 years of age. Medulloblastoma is associated with Basal Cell Naevus (Gorlin), Turcot and Blue Rubber syndromes. Clinical presentations include nausea, vomiting, headaches, ataxia, increasing head circumference and diplopia.

MRI is the definitive investigation for the diagnosis and staging of medulloblastoma and its potential subarachnoid metastases. Typical appearances are of a heterogeneous mass, which is hypo to iso-intense on T1, and hyperintense on T2 weighted images. Moderate to marked enhancement occurs with Gadolinium contrast on T1. Infrequently, cystic and necrotic areas are present (10-16%). Calcification occurs in 13% of cases where it is seen as a signal void. CT shows a rounded or lobulated homogenous high attenuation lesion that diffusely enhances with contrast.

Medulloblastoma is treated by surgical resection and radiotherapy to the craniospinal axis, usually in conjunction with chemotherapy. Overall pediatric 5-year survival is 50-60% with 40-50% alive at ten years. Cranio-spinal recurrence or metastases are evaluated using MRI imaging. Unfortunately, radiotherapy may be associated with mental and physical delay and with the development of radiation-induced tumours. It is hoped that future improvements in radiotherapy and chemotherapeutic regimes will lead to better survival rates and a reduction in unwanted side effects.