Medullomyoblastoma: a histological, immunohistochemical, ultrastructural and molecular genetic study

OTX2 represses myogenic and neuronal differentiation in medulloblastoma cells

The brain development transcription factor OTX2 is overexpressed and/or genomically amplified in most medulloblastomas, but the mechanistic basis for its contributions in this setting are not understood. In this study, we identified OTX2 as a transcriptional repressor and a gatekeeper of myogenic and neuronal differentiation in medulloblastoma cells. OTX2 binds to the MyoD1 core enhancer through its homeobox domain, and the remarkable repressor activity exhibited by the homeobox domain renders OTX2 transcriptionally repressive. RNA interference-mediated attenuation of OTX2 expression triggered myogenic and neuronal differentiation in vitro and prolonged the survival in an orthotopic medulloblastoma mouse model. Conversely, inducing myogenic conversion of medulloblastoma cells led to the loss of OTX2 expression. In medullomyoblastoma, a medulloblastoma subtype containing muscle elements, myogenic cells share cytogenetic signatures with the primitive tumor cells and OTX2 expression was lost in the differentiated myogenic cells. Thus, OTX2 functions via its homeobox domain as a suppressor of differentiation, and the loss of OTX2 expression is linked to the myogenesis in medullomyoblastoma. Together, our findings illustrate the origin of muscle cells in medullomyoblastomas and the oncogenic mechanism of OTX2 as a repressor of diverse differentiating potential.

[Medullomyoblastoma: a medulloblastoma with rhabdomyoblastic differentiation]

A 26 years old patient was operated for a tumor of cerebellar vermix, and then reoperated for a relapse at the age of 35 years, with a similar histological pattern in both cases. At pathologic examination, the tumor was composed of hypercellular sheets typical of medulloblastoma, containing also sparse large cells with eosinophilic cytoplasm and round nuclei containing voluminous nucleoli. Neuroblastic cells showed expression of neurofilament protein and synaptophysin. The large cells expressed desmin, myogenin, and neurofilament. These morphological and immunohistochemical features are characteristic of medullomyoblastoma. The patient deceased 11 years after the initial surgery. Medullomyoblastoma is a rare variant of medulloblastoma with a rhabdomyoblastic differentiation. The two tumoral populations share the same genetic alterations. The main differential diagnoses are atypical teratoid/rhabdoid tumor, immature teratoma, medulloepithelioma, primitive intracranial rhabdomyosarcoma and myoneurocytoma.

Cerebellar medullomyoblastoma with melanotic tubular structures

This report describes a midline cerebellar primitive neuroectodermal tumor with muscular differentiation, that is, medullomyoblastoma with melanotic tubular structures, which developed in the cerebellar vermis in a 23-month-old male. Rhabdomyoblastic differentiation consisted both of striated muscle fibers and undifferentiated cells showing immunoreactivity for desmin and myogenic transcription factors. The presence of melanotic epithelial structures raised the issue of a teratomatous tumor. This case demonstrates the occurrence of this very rare tumor in early childhood as well as the utility of a careful search for the presence of myogenic and/or melanotic features in medulloblastomas.

Medullomyoblastoma: a radiographic and clinicopathologic analysis of six cases and review of the literature

BACKGROUND

Medullomyoblastoma (MMB) is a rare cerebellar embryonal neoplasm that occurs almost exclusively in children. It is biphasic by microscopy, containing myoblastic and primitive neuroectodermal components.

METHODS

The authors conducted a retrospective review of the radiographic and pathologic characteristics, treatment, and clinical outcomes of six children with MMB who were treated at St. Jude Children's Research Hospital (Memphis, TN) between 1984 and 2003. Fluorescence in situ hybridization (FISH) data were available for four children. A literature review also was conducted and focused on imaging and pathologic findings.

RESULTS

The median age at diagnosis was 4.5 years (range, 0.83-7.5 years). Radiographically, all tumors were cerebellar and exhibited variable enhancement, and 50% of tumors had necrotic foci. Three tumors contained discrete, magnetic resonance imaging (MRI) T2-weighted-hypointense/computed tomography (CT)-hyperdense enhancing regions and separate hyperintense/hypodense nonenhancing regions, which correlated microscopically with geographic islands of primitive neuroectodermal and rhabdomyoblastic cells. Large cell/anaplastic (five tumors), nodular/desmoplastic (two tumors), and classic (two tumors) medulloblastoma histologies were encountered either alone (five tumors) or in combination with each other (two tumors). All 4 tumors that were tested exhibited alterations in chromosome 17 or c-myc amplification. All patients underwent macroscopic total resection and subsequently received chemotherapy and craniospinal (five patients) or local conformal (one patient) radiotherapy. At a median follow-up of 92 months (range, 23-187 months), 3 patients remain alive with no evidence of disease, 2 patients have died of disease, and 1 patient has died of secondary acute lymphocytic leukemia.

CONCLUSIONS

The results of the current study demonstrated the frequent correlation of biphasic nodularity (as determined by MRI or CT) with discrete rhabdomyoblastic and primitive neuroectodermal islands (as revealed by microscopy) in MMB. These results also support the view that MMB and medulloblastoma may have common tumorigenic origins, given their similar histologic and molecular features.

Medullomyoblastoma: case report

This 7-year-old boy presented with a 2-week history of headache, nausea, vomiting, anorexia, lethargy, and unsteadiness of gait. Brain magnetic resonance imaging (MRI) revealed a cystic mass within the vermis of the cerebellum. A suboccipital craniectomy was performed to remove a tumor that contained primitive neuroectodermal cells with florid skeletal muscle differentiation. Immunohistochemical studies and electron microscopy confirmed the presence of both a primitive neuroectodermal component and rhabdomyoblastic differentiation, consistent with the diagnosis of medullomyoblastoma. This exceedingly rare tumor of the cerebellar vermis of children is characterized by two components: primitive neuroectodermal tumor cells and skeletal muscle. Although the histogenesis remains uncertain, advances in immunohistochemistry and electron microscopy suggest the origin of this tumor from a multipotential stem cell precursor.

Molecular genetic classification of central nervous system malformations

Traditional schemes of classifying nervous system malformations are based on descriptive morphogenesis of anatomic processes of ontogenesis, such as neurulation, neuroblast migration, and axonal pathfinding. This proposal is a first attempt to incorporate the recent molecular genetic data that explain programming of development etiologically. A scheme based purely on genetic mutations would not be practical, in part because only in a few dysgeneses are the specific defects known, but also because several genes might be involved sequentially and many genes inhibit or augment the expression of others. The same genes serve different functions at different stages and are involved in multiple organ systems. Some complex malformations, such as holoprosencephaly, result from several unrelated defective genes. Finally, a pure genetic classification would be too inflexible to incorporate some anatomic criteria. The basis for the proposed scheme is, therefore, disturbances in patterns of genetic expression; polarity gradients of the axes of the neural tube (eg, upregulation or downregulation of genetic influences); segmentation (eg, deletions of specific neuromeres, ectopic expression); mutations that cause change in cell lineage (eg, dysplastic gangliocytoma of cerebellum, myofiber differentiation within brain); and specific genes or molecules that mediate neuroblast migration in its early (eg, filamin-1), middle (eg, LIS1, double-cortin), or late course (eg, reelin, L1-CAM). The proposed scheme undoubtedly will undergo many future revisions, but it provides a starting point using currently available data.