Abstract
A 20-year-old male patient presented with signs and symptoms of raised intracranial tension. CT scan confirmed a right lateral cerebellar tumor. An emergency VP shunt was performed. However the patient succumbed within 4 days of presentation. A complete autopsy undertaken showed the presence of bilateral pulmonary nodules in addition to the right cerebellar tumor. Immunohistochemistry supplemented with cytogenetics confirmed the presence of pulmonary metastases of medulloblastoma. We highlight the rare presentation of spontaneous pulmonary metastases of an adult medulloblastoma.

Case Report
A 20 year old male presented to the out patient department with chief complaints of headache, neck pain and drowsiness since 8 days. On complete physical examination, there were signs of raised intracranial tension with bilateral papilloedema. The CT scan showed the presence of a right cerebellar tumour, a fairly homogeneous, high density mass measuring 7 cm x 5 cm x 3 cm. An emergency VP shunt was inserted to relieve the symptoms. The cerebrospinal fluid obtained during this procedure showed a count of 14 lymphocytes /cmm and proteins of 216.9 mg%. No malignant cells were seen on cytology. Patient expired 4 days later. A complete autopsy was performed which showed an oedematous brain weighing 1300 grams. A grayish white mass measuring 6.5 cm x 4.5 cm x 3 cm was seen in the right cerebellar hemisphere. The mass was attached to the dura extending through the tentorium and indented the right temporal lobe. Histology revealed a highly cellular tumour composed of monotonous looking small round cells with vesicular nuclei and scant eosinophilic cytoplasm. At places a perithelial arrangement was seen. However, there was no evidence of Homer Wright rosettes or pseudorosettes.There were no foci of glial or ependymal differentiation (Fig. 1). Focal areas of necrosis were seen. The tumour was seen to infiltrate the dura but there was no evidence of desmoplasia.

Lungs showed presence of whitish nodules ranging from 3-5 mm in diameter in both the upper lobes. The histology of these nodules was similar to that of the cerebellar tumour (Fig 2). Pleural and peritoneal cavities were normal. Rest of the organs showed no specific pathology. A provisional diagnosis of malignant round cell tumour of primary brain origin with secondaries in the lung was entertained. The differential diagnoses offered were Medulloblastoma and Non Hodgkin's lymphoma.

On immunohistochemistry, both the brain tumour and the lung nodules were positive for Synaptophysin, Neuron Specific Enolase and S100 protein. However, they were negative for Leucocyte Common Antigen, actin and cytokeratin. Electron microscopy results were inconclusive due to formalin fixation of the brain at autopsy. Further, cytogenetic study revealed increased c-myc mRNA expression and deletion of 17p and isochromosome 17q. Thus the above findings confirmed the diagnosis of Medulloblastoma with pulmonary metastases.

Fig. 1 : Photomicrograph from the cerebellar lesion shows a highly cellular small round cell tumour [x 100X].	Fig. 2 : Photomicrograph from the lung nodules shows similar histological features as seen in the cerebellar tumour [x 40X].

Discussion
Extracranial metastases of primary CNS malignancies are rare. Though medulloblastoma is considered to be a highly malignant tumour, metastasis from medulloblastoma outside the craniospinal axis is rare, with an overall incidence of around 7.1%.^1,2 Breakage of blood-brain barrier by various pathways has been considered as the foremost method of spread for primary CNS malignancies. There is a greater incidence of metastases following surgery and V-P shunt procedures.¹ Further, according to Duffner PK and Cohen ME, post-chemotherapy induced metastases are based on immune alterations.³ Palacios E et al have considered haematogenous spread as a possibility in their study by post-operative CT scans and detailed autopsy examinations.⁴

Glioblastoma multiforme and medulloblastoma are the two common of the malignant brain tumours to spread outside the central nervous system, but the pattern of spread is different for each of these tumours. Skeletal metastases are two times more frequent in medulloblastoma than in glioblastoma.1,2 Conversely, the lung is the most frequent site of involvement in glioblastoma (60%) but is much less frequently involved (13%) in medulloblastoma.^1,2

Campbell AN et al have described that both adults and children can develop metastases of medulloblastoma.⁵ According to Rochkind S et al, bone and bone marrow is the most frequent site of metastases of medulloblastoma (77%) followed by lymph nodes. They further describe lung (17%) and liver (13%) to be the next most common site in adults and children respectively^{1 5}

In 1936 Nelson reported the first well-documented case of metastasis outside the central nervous system in a patient with cerebellar medulloblastoma.^2,6 In 1955, Weiss proposed rigid criteria for diagnosing extracranial metastases from primary CNS malignancies. These include a single histologically characteristic CNS tumour, a clinical history indicating a primary CNS lesion, a complete postmortem examination to exclude peripheral primaries and similar histological findings of the CNS and the peripheral lesions.^1,2,7 Our case fulfills all the criteria laid down by Weiss. Further, immunohistochemistry and cytogenetic applications confirmed that both the primary CNS lesion and the lung nodules were similar.

We further conclude that a thorough search for early identification of extracranial metastases of primary CNS tumours is mandatory.

Acknowledgements
We would like to thank Dr S K Pandya, Professor and Head of the Neurosurgery Department, Seth G.S Medical College and KEM hospital for the help rendered during the study. We would also like to express our gratitude to the Dean of Seth G.S Medical College and KEM Hospital for allowing us to publish the hospital data.

References

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