• Iatrogenic benign mass composed of fungi-like spherules that are actually erythrocytes damaged by endogenous and exogenous fat

• First described by McClatchie (E Afr Med J 1969;46:625), who reported 7 patients from Kenya with unusual soft tissue nodules in arm, legs and subcutaneous tissue of buttock
• Called myospherulosis due to the involvement of skeletal muscle in some patients (Am J Clin Pathol 1969;51:699)
• Five patients were subsequently reported by Hutt in Uganda (Trans R Soc Trop Med Hyg 1971;65:182)
• Initially these structures were thought to be a fungus, but the usual stains for fungi were negative
• Kyriakos (Am J Clin Pathol 1977;67:118) reported non-African cases in paranasal sinuses, nasal cavity and middle ear; most patients had undergone surgery and the surgical wound was packed with gauze impregnated with petrolatum and tetracycline ointment, suggesting an iatrogenic etiology
• De Schriver and Kyriakos confirmed this etiology by inducing similar lesions in experimental animals (Am J Pathol 1977;87:33)
• Rosai (Am J Clin Pathol 1978;69:475) and Wheeler (Arch Otolaryngol 1980;106:272) demonstrated that the spherules were erythrocytes damaged by endogenous and exogenous fat
• Travis (Arch Pathol Lab Med 1986;110:763) and Shimada (Am J Surg Pathol 1988;12:427) confirmed the presence of damaged erythrocytes by immunostaining for hemoglobin
• Kakizaki (Am J Clin Pathol 1993;99:249) demonstrated that the wall of the spherules was due to the physical emulsion phenomenon that occurs between lipid-containing materials and blood
• The damaged erythrocytes are enclosed by a lipid membrane and later phagocytosed by histiocytes as part of the lipogranulomatous reaction that takes place in adipose tissue

• Due to erythrocyte damage from endogenous and exogenous fat
• Also due to endogenous membranocystic degeneration of fat that occurs in lupus erythematosus and in membranous lipodystrophy with dermal atrophy due to local application of steroid ointment (Arch Dermatol 1991;127:88)
• In the gluteal region, this entity is described in relation to old injections of petrolatum based hormones and penicillin (Diagn Cytopathol 1988;4:137, J Am Acad Dermatol 1989;21:400)

• May occur with aspergillosis of the maxillary sinus (Oral Sur Oral Med Oral Pathol 1987;63:582, Arch Pathol Lab Med 2005;129:e84)

• 39 year old man with large buttock tumor (Case of the Week #173)
• 60 year old man with retroperitoneal tumor (Asian J Neurosurg 2010;5:91)

• Benign process; no treatment needed other than for symptomatic relief

• Large saccular cyst-like lesion, surrounded by fat
• May contain oily substance with a yellow color

Buttock tumor

Large gluteal mass

• Cyst composed of spherules which are damaged erythrocytes
• Wall of the cyst made of fibrous tissue, accompanied by a lipogranulomatous reaction
• Many eosinophilic spherules containing red blood cells are within histiocytes lining the cyst wall
• Some larger spherules resemble a bag of marbles
• Dermal nodules are cystic cavities with a fibrous wall lined by histiocytes and multinucleated foreign-body giant cells, with lipogranulomatous inflammation in the adipose tissue adjacent to the cavities

Gluteal mass

Case of the Week #173:

Buttock tumor

• PAS for fungi, GMS

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