Myelolipomas are benign neoplasm-like nodules composed of various quantities of mature adipose cells and hematopoietic cells. These well-vascularized extramedullary masses may be encapsulated or may blend into surrounding tissues. Myelolipomas have been reported in the spleen [6] and liver [3, 41 of the domestic cat, the spleen [2] and liver [5, 71 of the cheetah (Acinonyxjuhalus) and the liver of the Siberian tiger (Felis tigris longipilis) [5]. A myeloliposarcoma has been reported in the inguinal region of a potto (Perodictictu potlo) [I]. There are no reports of this condition in dogs.Myelolipomas were found in two dogs. Dog A was a 12-year-old, intact female, miniature schnauzer which had no clinical signs associated with the splenic mass. The mass measured 7 cm in diameter, was tan and had a fat-like appearance on the cut surface. Dog B was a 12-year-old, spayed miniature schnauzer with a history of abdominal enlargement. The splenic mass measured 6 X 6 x 8 cm and was mottled red-to-tan and soft.Microscopically, masses from both dogs had similar components but vaned in the ratio of adipose cells to hematopoietic cells. The mass from dog A consisted of small groups of relatively mature erythroid and myeloid cells interspersed between a large number of mature adipose cells ( fig. I). No capsule was evident, but the mass was well demarcated from the surrounding parenchyma. Massive extramedullary hematopoiesis, both erythroid and myeloid, widely dispersed the adipose wells in the splenic mass from dog B (fig. 2). The cell population consisted of cells in all stages of differentiation-most were relatively immature. The nodule was unencapsulated and blended into the surrounding splenic parenchyma. Multiple foci of nodular hyperplasia were observed in the spleen. These two dogs had masses which represented opposite extremes in ratios of adipose to hematopoietic cells. Various cell ratios between masses of different animals have been reported [ 5 ] , and therefore would not be considered unusual in dogs. It is interesting, though probably not significant, that these two myelolipomas occurred in the same breed. Myelolipomas previously had been described only in domestic and wild Felidae. This report demonstrates that dogs also can develop myelolipomas.

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