Neuromuscular hamartoma (benign "Triton" tumour) in a mouse.

Histological examination of a 22-month-old CD-1 mouse revealed a threefold enlargement of the right trigeminal ganglion. This change was due to the presence of well-differentiated striated muscle fibers intermingling with nerves and ganglion cells. The number of ganglionic Schwann cells was also increased as demonstrated by their positive S-100 protein staining. In addition, slight interstitial mononuclear cell infiltration and fibrosis were observed. The myocytes, which stained positive for myoglobin and desmin, and the proliferated Schwann cells did not show any signs of cellular or nuclear atypia. The lesion was diagnosed as "neuromuscular hamartoma (benign "Triton" tumor)" reflecting the capability of either Schwann cells or neural crest derived precursor cells to differentiate into various other cell types.