Department of Pathology, University of Oklahoma Health Sciences Center

NeuroTest Question #62 Next question Previous question

Answer: Medulloepithelioma (B).  Level of difficulty: 3 NeuroTest NeuroLearn NeuroHelp

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Discussion:

Pathology of the case:

• On high-magnification, the tumor is composed of cords of pleomorphic epithelial cells. It appears that the tumor cells are forming a lumen (Panel A). On Jones stain, a layer of basement membrane is demonstrated on one side of the lumen but not the other side (Panel B). The other side of the tumor seems to be the luminal side of the structure. These features, together with the history and anatomical location, are most compatible with medulloepithelioma.

Medulloepithelioma: 

• In essense, medulloepithleioma is a malignant (WHO grade IV) neuroectodermal tumor that recapitulates the earliest developmental stage of the central nervous system, the neuroepithelial stage. It is a rare tumor, occurs in children under 5 years of age, occurs both as supratentorial and infratentoral tumor, has no sex predilection. Medulloepithelioma arising in the central nervous system carries a grave prognosis.
• Tumor cells arrange in of tubules or strands, bands, or cords of cylindrical or columnar epithelium. The inner or luminal surface is well defined and consist of protruding blebs on the luminal surface. In contrast to ependymomal rosettes, there is no blepharoplasts or cilia on the luminal side of the epithelium. There are structures suggesting the existence of both internal and extermal limiting membrane in the tubular structure which are both PAS(+). The external membrane may be more prominent and is positive on immunostaining against collagen type VI basal lamina and can also be demonstrated by reticulin stain and Jones stain. [Click here to see more pictures of medulloepithelioma]
• These tubular structures are surrounded by a connective tissue stroma. The mesenchymal stroma varies widely from cases to cases. Bone, cartilage, or muscle can be be found.
• In contrast to ependymoblastoma, the tumor cells surrounding these rosettes are well delineated from the tubules by the membrane. In ependymomas, the surrounding primitive cells tumor cells will merge with the cells of the tubules. Mitotic figures are abundant and are usually found near the luminal surface, as in embryonic neural tubes.
• Maturation of these primitive cells into neuronal, astrocytic, ependymal and oligodendroglial components can occur and the extent of differentiation is variable. 
• Immunohistochemistry: the tumor cells are always positive for nestin and usually negative for keratin (focal keratin positivity may be seen occasionally). They may also be positive for neurofilament, cytokeratin, epithelial membrane antigen, neuron specific enolase, synaptophysin, microtubule-associated proteins, and GFAP.

Medulloblastoma:

• Medulloblastoma recapitulate a slightly later developmental stage than that of medulloepithelioma. They are solid tumors and no tubular structures are formed. The location of the current case is supratentorial. As per the WHO classification, tumors that occur in the supratentorial location and spinal cord and have features of medulloblastoma are called primitive neuroectodermal tumor (PNET). [Click here to see histologic picture of medulloblastoma] [Click here to see cytologic preparation of medulloblastoma]

Dysembryoplastic neuroepithelial tumor (DNET):

• DNET can occur in this location at this age and can be cystic. However, it is of WHO histologic grade I. The histology is completely different. DNET has both glial and neuronal component and does not form tubules that are found in medulloepithelioma.

Subependymal giant cell astrocytoma (SEGA):

• SEGA typically present as intraventricular nodule or mass in patients with tuberous sclerosis. Histologically, the cell can appear large and bizarre. However, there is no tubule formation. [Click here to see a picture of a subependymoma giant cell astrocytoma]

Anaplastic astrocytoma:

• The histology of astrocytoma is completely different from that of medulloepithelioma. [Click here to see a picture of anaplastic astrocytoma]

Comment: KarMing-Fung@ouhsc.edu