Ultrastructural changes in medullomyoblastoma. Similarities with foetal rhabdomyoma.

The light and electronmicroscopic changes are described in two cases of medullomyoblastoma, and compared with the changes seen in a case of foetal rhabdomyoma. The medullomyoblastomas in two children aged 8 and 5 years, consisted predominantly of classical type of medulloblastoma cells, along with few to many 'strap cells' or 'myoid cells' which, on closer examination, showed clear cross striations, consistent with muscle fibres or myofibrils. The primitive myoid cells were similar to those encountered in larger numbers in a post-auricular rhabdomyoma, possibly of foetal origin in a 40 day old infant. The four pathogenetic mechanisms i.e. (i) an embryonal stage of myofibrillar differentiation; (ii) a malformative factor; (iii) a teratoid factor on account of the presence of mesenchyme derived striated muscle tissue in the obviously predominant ectodermal medulloblastoma; and (iv) metaplasia of the vascular smooth muscle cells in the medullomyoblastoma, are discussed.

Utility of silver-colloidal staining method in the diagnosis of medulloblastoma.

Histopathological features of medulloblastomas are usually distinctive. However in rare instances, a distinction between the neoplastic cells of medulloblastoma and the neurones in the cerebellar internal granular layer becomes difficult at light microscopic level. In order to distinguish presence of argyrophilic Nucleolar Organizer Regions (Ag-NORs) was analysed in the paraffin sections of medulloblastoma as well as in the cerebellar internal granular layer. The neoplastic cells in medulloblastoma contained a mean 4.78 Ag-NOR per nucleus while the neurones in cerebellar internal granular layer contained a mean Ag-NOR 0.90 +/- 0.12 per nucleus. Compound Ag-NORs were present in the cells of medulloblastoma while they were absent in the neurones of cerebellar internal granular layer. The results of this study indicate that Ag-NOR technique may be useful in an uncommon situation, where a histopathological distinction between cells of medulloblastoma and neurones in the cerebellar internal granular layer becomes difficult.