Presacral myelolipoma. Report of a case with fine needle aspiration cytology and immunohistochemical and histochemical studies.

The cytomorphologic features of a case of the rare presacral myelolipoma, diagnosed by computed tomography (CT)-guided percutaneous fine needle aspiration (FNA) biopsy, are presented. It occurred in a 40-year-old man on prolonged steroid therapy for bronchial asthma. On the air-dried, Diff-Quik-stained smear, hematopoietic cells of all lineages and fragments of collapsed stroma were seen in a background of fat droplets. Megakaryocytic, myelocytic and eosinophilic lineages were further demonstrated by Factor VIII immunostain, chloroacetate esterase and LUNA-E histochemical stain, respectively. The reticulum stain of the resected tumor demonstrated that the hematopoietic cells and fat were supported by numerous reticulum fibers of varying thickness; that accounted for the collapsed stroma in the aspirated material. Presacral myelolipoma, occurring predominantly in female adults and presenting secondarily as a space-occupying lesion, is best regarded as encapsulated, heterotopic bone marrow supported by a network of reticulum fibers; it has a characteristic image on CT scan and can be diagnosed by FNA.