Crystalline inclusions in a subependymal giant cell tumor in a patient with tuberous sclerosis.

Unusual crystalline cytoplasmic inclusions were encountered in tumor cells in a subependymal giant cell tumor (SEGT) in a 16-year-old girl with tuberous sclerosis. By electron microscopy, the tumor cells demonstrated typical features previously described in SEGT, including abundant dense bodies, prominent Golgi complexes, abundant mitochondria, rough and smooth endoplasmic reticulum, scattered intermediate filaments and microtubules, glycogen, and rare synaptic contacts as well as primitive intercellular junctions. The dense bodies were bound by a single membrane and were round, ovoid, irregular, or cylindric in appearance with electron-dense homogenous content or fingerprint profiles. Of note was the presence of numerous cytoplasmic rhomboidal or rectangular crystalline inclusions akin to those seen in alveolar soft part sarcoma. These inclusions measured as much as 8 microns in length and had 7-nm periodicities, often with intersecting lamellae. Rarely, the membrane-bound dense bodies showed areas of similar periodicities, indicating that the crystalline inclusions are related to and might originate from the dense bodies. While crystalline inclusions have previously been described in one patient with SEGT (Bender and Yunis, Ultrastruct Pathol 1980; 1:287-299), the inclusions in the present case were a striking feature and add to the spectrum of the ultrastructural pathology of SEGT.