Pediatric Medulloblastomas

I. Introduction-Definition

Medulloblastoma (MB) is a Primitive Neuroectodermal Tumor (PNET) located in the Posterior Cranial Fossa (FCP). It is a malignant cerebellar tumor (WHO grade IV), with a predominant neuronal differentiation and a tendency to spread via cerebrospinal fluid (CSF) (37). It represents 40% of cerebellar tumors, 15% of all brain tumors and is the primary cause of malignant brain tumor in children (54). In France, an estimated number of 100 new cases are diagnosed yearly. The overall five years survival rate is about 75% to 80% in the absence of metastases. Metastasis is one of the main prognostic factors (5, 25). All the advances made with stratified analysis of the patients has led to few cases in each subgroups thus a need for an international collaboration to harmonize diagnostic and therapeutic strategies and long-term monitoring.

II. History

The term ’medulloblastoma’ was originally introduced by Percival Bailey, who was working with Harvey Cushing: ’ In 1925, I isolated a type of glioma which occurs chiefly in the center of the cerebellum of children for which I suggested the name medulloblastoma ’(3). Thereafter, Harvey Cushing published a comprehensive study on this tumor entity (14). The term has remained till date. It is worth noting that for these authors, the MB is assumed to be a glial tumor, even though descriptions of histological preparations are very precise and similar to those currently performed. We invite readers interested in the history of MB to refer to the article by Rutka and Hoffman (59).

III. Natural History

The natural history of primitive neuroectodermal tumor remains debatable (4). These tumors, of the PCF, tend to infiltrate the fourth ventricle and sometimes the floor. MB can spread along the neuraxis in about one in three children and exceptionally outside the central nervous system (see following paragraphs). The tumor originates in the cerebellar vermis in 75% of cases (then invades the fourth ventricle); it is rarely located in the cerebellar hemispheres (37).

As with any CNS malignancy, the duration of symptoms before diagnosis is relatively short, compared to benign or low grade lesions. However, this duration can be variable for children with MB (6, 31, 70). In a large prospective study, the time to diagnosis ranged from 0 to 2 years, with a median of 2 months (23).