Differential Diagnosis: Medulloblastoma
Based on the location, type of tumor and age of the patient, the clinical presentation of the child in this case points to considering medulloblastoma as one of the differential diagnoses. In this case, the patient presented with intermittent headache and vomiting of one year. His symptoms and age are consistent with an infratentorial brain tumor, like medulloblastoma.
Medulloblastoma is the most common malignant tumor in children, accounting for 10-20% of primary CNS neoplasms and about 40% of all posterior fossa tumors. It is a cerebellar tumor occurring mostly in males at a median age of 5 to 7 years old. It is a highly invasive embryonal neuroepithelial tumor that arises in the cerebellum and has a tendency to disseminate throughout the CNS early in its course.
Medulloblastomas commonly arise from the midline cerebellar vermis, though older patients may have tumors in the cerebellar hemispheres. Patients may present with signs and symptoms of increased ICP (like headache, nausea and vomiting, mental status changes, and hypertension) and cerebellar dysfunction (ataxia, poor balance, dysmetria). This patient presented with headache, nausea and vomiting—which are consistent with increased ICP. The CT scan of this patient revealed a slight enhancing heterogenous hyperdense lesion in the cerebellar vermis with perilesional edema and mass effect, as well as moderate extraventricular obstructive hydrocephalus. In medullobastoma, CT and MRI may demonstrate a solid, homogenous, contrast medium-enhancing mass in the posterior fossa causing 4th ventricular obstruction and hydrocephalus. The clinical manifestations of the patient and the imaging results confirm a cerebellar lesion.
In this case, medulloblastoma is considered because of the patient’s history of headaches and emesis, which are early symptoms of increased ICP. Seventy to ninety percent of patients with medulloblastomas present with a history of headaches, emesis and lethargy, and these symptoms are generally intermittent and subtle. A duration of symptoms for 3 months or longer prior to diagnosis is common. The increase in ICP, as a consequence of hydrocephalus, may have caused the sixth cranial nerve to be compressed at the petroclival ligament, resulting in diplopia and lateral gaze paresis. This patient presented with limited lateral eye movements on the left on the sixth hospital day. Examination of the extraocular muscles may detect nystagmus, which, although nonspecific, can be related to a lesion of the cerebellar vermis. Horizontal nystagmus was observed in the patient upon neurological examination.
However, medulloblastoma can also be ruled out due to its potential to metastasize to the neuraxis. Though it is the most common group of malignant CNS tumor and it has propensity to occur in the midline cerebellar vermis as in this patient, the long duration of symptoms of the patient without intervention could have allowed for metastasis to occur, especially since this type of tumor has a potential to metastasize. Patients with disseminated disease at diagnosis (M>0), including positive CSF cytology alone (M1) have a markedly worse outcome. Other midline posterior fossa tumors, like cerebellar astrocytoma may have a similar appearance on CT, but occur more commonly than medulloblastoma.
Sources:
Nelson’s 18th Ed.
eMedicine.