Figure 1. Cystic tumor (6 × 5 × 4.5 cm) in the right cerebellum. The largest cyst measures 3 cm in diameter and is filled with greenish fluid.
Figure 2. Undifferentiated areas composed of cells with small hyperchromatic nuclei and inconspicuous cytoplasm. The cells are arranged in cords and trabeculae (hematoxylin-eosin, original magnification ×280).
Figure 3. Marked desmoplasia with connective tissue encircling single cells or groups of cells (reticulin stain, original magnification ×550).
Figure 4. Scattered ganglion cells in a fibrotic background (hematoxylin-eosin, original magnification ×280).
At autopsy, the brain weighed 955 g. The right cerebellum contained a cystic tumor measuring 6 × 5 cm. Medulloblastomas are dense small cell tumors. They are heterogeneous but as a group are known for small hyperchromatic condensed nuclei and inconspicuous cytoplasm. There are several classifications: undifferentiated, neuroblastic differentiation, glial differentiation, mixed glial neuronal differentiation, and divergent differentiation.1 The desmoplastic variant of cerebellar medulloblastoma2 formerly identified by some workers as an arachnoidal cerebellar sarcoma3-5 is a superficial well-circumscribed form of medulloblastomas that predominantly occurs in young adults. Desmoplastic medulloblastoma has less nodularity compared with the other counterparts and a higher content of reticulin surrounding single cells or groups of cells. Abundance of connective tissue lends firmness to the tumor. The unique features of this case include (1) multiple cysts; (2) marked desmoplasia in a 1-year-old child; and (3) three types of clear-cut areas with abrupt transition: undifferentiated areas, mesenchymal areas with ganglion cells, and transition areas with follicular architecture (ie, pale islands).