Medulloblastoma.

Clinical History

Three months old male with an increased head size, nausea and vomiting.

Imaging Findings

The patient was admitted to the hospital because of an increased head size and symptoms of raised intracranial pressure. The following radiographic examinations were performed: cranial US, CT scan of the brain, and MRI. After the CT examination and before the MRI study was performed, the patient suffered clinical deterioration which required a CSF shunt insection. An intraoperative biopsy was done which confirmed the pathologic diagnosis. Unfortunately the child did not survive the surgery and died few hours later in the intensive care department.

Discussion

Brain tumor presenting during the first year of age are frequently aggresive with a poor prognosis. Medulloblastomas are included in the histopathological group of the Primitive Neuroectodermal Tumors (PNET), originating from primitive or undifferentiated embriologic cells with the capacity to differentiate along neuronal, glial or mesenquimal lines. They are highly malignant hypercellular tumors composed mainly of small hyperchromatic round cells having only a minimal rim of cytoplasm. The tumor commonly arises from the cerebellum and grows anteriorly into the roof of the fourth ventricle and posteriorly to the cisterna magna until causing obstruction of CSF flow and subsequent hydrocephalus, which explains the shortness duration of symptoms ( nausea, vomiting, increasing head size, headaches and ataxia). Cerebellar PNETs can be found associated with several syndromes as Gorlin´s basal cell nevus syndrome, Turcot syndrome or ataxia-telangiectasia but these entities are very rare. Medulloblastomas account for 30-40% of posterior fossa brain tumours in children, but are rare in adults. The characteristic features of medulloblastoma on CT are well-defined hyper or isodense masses of the cerebellum showing mild enhancement after IV contrast administration, surrounded by moderate oedema and associated hydrocephalus (up to 95% of cases). MR usual findings are midline or paramedian tumors, relatively homogeneous and hypointense on T1, but characteristically heterogeneous and iso or hypointense on T2. They usually enhance after administration of paramagnetic contrast. Although these are the classical features of medulloblastoma, “atypical” presentation occurs in approximately 47-60% of patients, including calcifications (15-50%), cystic or necrotic areas (50-75%), intratumoral hemorrhage, lack of enhancement or eccentric location. The differential diagnosis of posterior fossa tumors in the first year of life include not only medulloblastoma but also cerebellar astrocytoma and primary atypical teratoid/rhabdoid tumor essentially. The diagnosis based upon the image is very difficult. Some features help to suggest one or another histology. For example, astrocytomas are more often hipodense on CT scans prior to contrast infusion whereas medulloblastomas are iso or hiperdense; and teratomas are usually midline roughly calcified masses affecting infra and supratentorally which can contain fat components. The prognosis is very poor, even when surgical removement is feasible and radiotherapy associated, the survival rate after 5 years is still less than 50% . That is because medulloblastomas have a high tendency to invade the leptomeninges and spread throughout the CSF, disseminating widely in CNS. Furthermore PNETs are the most likely CNS tumors to bring systemic metastases (bone (5%), followed by lymph nodes and lung).

Differential Diagnosis List

Final Diagnosis

Final diagnosis: Medulloblastoma.

URL:	https://eurorad.org/case/4578
DOI:	10.1594/EURORAD/CASE.4578
ISSN:	1563-4086