Myospherulosis in Renal Cell Carcinoma.

Myospherulosis was first described in Africa by McClatchie et al.[1] The name was used based on the suspicion that this may be a curious new fungal infection. It is now known that these structures represent altered erythrocytes. The cases reported in the literature to date can be divided into 2 categories: those iatrogenic cases where causality with petroleum-based ointment and gauze packs could be found, such as those seen in the paranasal cavity,[2-4] in the ocular cavity,[5] intracranially,[6] and in dermal tissue,[7] and those cases where erythrocytes are altered by endogenous fat or lipids. Examples include cases found in subcutaneous tissue,[8] breast tissue,[9] perirenal adipose tissue,[10] steatocystoma,[11] and an adjacent benign cystic teratoma.[12]

In the first cases described in Kenya,[1] the myospherules were round bags of spherules surrounded by a thin, somewhat refractile membrane under light microscopy. The spherules were said to be slightly larger than red blood cells and closely and irregularly packed together. No obvious internal structure was seen, but in some there were small granules or irregular blobs of eosinophilic material. Their sizes were not mentioned. From the photo plates, they ranged from about 10 to 15 spherules in diameter. They were located within cysts surrounded by fibrous tissue, histiocytes, and giant cells. Some of the myospherules were ingested by giant cells in the cyst wall. The spherules and their casing did not take up any stains for fungi, although they were suspected to be organisms such as Rhinosporidium or Coccidioides. Subsequently, similar cases were identified in North America, where they were almost exclusively found in the upper respiratory tract.[2-4] In the case reported by Rosai,[2] they were described as sacs of 2 or 3 to more than 100 spherules 4 to 7 [micro]m in diameter. Under hematoxylin-eosin staining, some spherules had a thin, pale, eosinophilic membrane. Others had a brown, thicker, and coarser membrane, with irregular granularity on the outside. The latter appearance was interpreted as deposition of a foreign material onto a pre-existing biologic structure.

The pathogenesis of myospherulosis was confirmed experimentally by Rosai[2] and Wheeler et al,[3] who reproduced it by incubating human erythrocytes at body temperature with tetracycline ointment, lanolin, petrolatum, and liquefied human fat. Ultrastructural examination by Rose et al[13] revealed that some spherules contained dense bodies and filaments. They also had a double electron-dense wall: the outer layer had a thickness corresponding to that of…