DIAGNOSIS: Pineal anlage tumor (without immature components) DISCUSSION:
The presence of the melanin-containing cell clusters in this case may evoke the association with tumors designated as "retinal anlage tumors" (Table 1). These lesions, also known by the term "melanotic neuroectodermal tumor of infancy" (MNTI) or "melanotic progonoma" are usually found in the infant jaws. Similar tumors have been described intracerebrally where they generally carry an unfavorable prognosis (9). MNTI-like tumors have been reported in the pineal region and were named "pineal anlage tumours" (2, 3, 5). Primary pineal parenchymal tumors may give rise to a broad spectrum of differentiation (5, 8, 10) reminiscent of embryonic pineal cells which are able to differentiate into striated muscle fibres, pigmented epithelial cells and neuronal cells (1, 11). Apart from differentiated and undifferentiated neuronal cells, retinal receptor-like cells, ependymal cells and the melanotic epithelial cells, mature and immature cartilage and striated muscle cells have been described in the pineal anlage tumor (6, 9, 11). While the MNTI is generally a benign lesion, its cerebral counterpart usually harbors primitive tumor cells and is definitely malignant. Extracerebral MNTIs differ from the malignant cerebral tumors in immunoreactivity for HMB-45, EMA and cytokeratin. Since the pineal gland is a derivative of the neural crest, the pineal anlage tumors may also have derived from neural crest cells (ectomesenchyme) and thus overlap with the constituents of the ectomesenchymomas is obvious.
The term "ectomesenchymoma" was coined for tumors consisting of ectodermal components (usually neuronal cells and S100-positive spindle cells) in combination with embryonal rhabdomyosarcoma . Ectomesenchymomas have been described in a variety of tissues (4) including the orbit (6) and the CNS (5). A problem in making the diagnosis ectomesenchymoma in the present case is the lack of a primitive tumor component, viz., rhabdomyoblastoma. For the same reason, namely, the absense of immature rhabdoid cells, the present case also differs from medullomyoblastomas occurring in the cerebellum (regarded as variant medulloblastomas) and an even more rare tumor called "myoneurocytoma" that was described in the cerebellum of a 6-year-old boy and consisted of immature muscular cells with a mature neuronal component (8). The diverse cell populations of these various tumors is, however, suggestive of an origin from pluripotential neural crest cells (ectomesenchyme) or neural groove.
The present tumor cannot unequivocally be classified into any current classification or nomenclature and we have not found an equivalent case in the literature. Therefore, various diagnoses may be appropriate but we prefer to classify it within the group of pineal anlage tumors. Strictly, diagnoses as "bidermal mature teratoma of the pineal gland" or "melanotic benign ectomesenchymoma", "ectomesenchymal hamartoma" would be even appropriate. The pathogenesis, key to a definite term for this neoplasm, remains obscure.
+ = sometimes or always present
- = never or very unusually present
Contributed by Inga Gudinaviciene, Darius Pranys, Pinping Zheng and Johan M. Kros