Subcutaneous palisading granulomatous pseudocysts of Echinococcus granulosus origin.

Background: Palisading granulomatous reactions are documented in many diseases. Although subcutaneous cystic echinococcosis (CE) is documented rarely, a subcutaneous palisading, granulomatous, pseudocystic (PGP) reaction to elusive Echinococcus granulosus membranous components, in the absence of cutaneous fistulization, is undocumented.

Methods: Seven-year clinicopathological review of subcutaneous echinococcal PGP reactions.

Results: Gross: seven thick-walled 'cysts' containing clear or straw-colored fluid were investigated. Histopathology: the pseudocysts contained a palisade of epithelioid histiocytes and giant cells. Focal periodic acid Schiff (PAS)-positive eosinophilic fragments, some resembling keratin 'flakes', were identified within the lumen or within the cellular palisade, consistent with a PGP reaction to fragmented E. granulosus membrane. Clinical correlation: the initial histopathological diagnosis of two patients was ruptured epidermoid cysts with an assumed granulomatous reaction to eosinophilic keratinous debris. Subsequent diagnosis of CE in the liver and cervical soft tissue necessitated review of the 'epidermoid cysts'; PAS-positive E. granulosus membranous fragments masqueraded as keratinous debris. Renal, hepatic and pleuropulmonary CE were confirmed in the remaining patients following confirmation of an echinococcal PGP reaction.

Conclusion: Heightened awareness and obsessive appraisal of subcutaneous PGP reactions for subtle, focal, PAS-positive and echinococcal membranous fragments are pivotal to the diagnosis that also serves as a clue to visceral CE.