Pathological significance and clinical features of myelolipomas in dogs and cats: A retrospective study of 2697 cases.

Myelolipomas are benign proliferations of well-differentiated adipose and hematopoietic tissue. Myelolipomas are reported to arise in the spleen, liver, and adrenal gland. Splenic myelolipomas rarely result in hemoabdomen or splenic rupture. In dogs and cats, no reports associate the formation of hematomas with splenic myelolipomas. The few published cases of myelolipoma have precluded the determination of breed and sex predisposition. A total of 2697 cases of myelolipomas were retrieved, comprising 96.3% (2596/2697) dogs and 3.7% (101/2697) cats. In dogs, splenic hematoma arising from myelolipoma was reported in 39.8% of the cases (1017/2554) and was a significant risk factor for both hemoabdomen (11.8% vs 2.0%; odds ratio [OR], 6.138; P < 0.001) and splenic rupture (13.9% vs 3.5%; OR, 3.898; P < 0.001). In cats, splenic hematoma, hemoabdomen, and splenic rupture caused by myelolipomas were infrequent, and half of the hepatic myelolipomas arose within peritoneopericardial diaphragmatic hernias (PPDH). In dogs, Labrador retrievers were the most affected breed (13.6%; 354/2596), and the mean age at the time of diagnosis was 11.4 years (range 1-18 years). The mean mass diameter was 7.4 cm (range 0.2-35 cm). The spleen (98.2%; 2550/2596) and adrenal gland (1.3%; 35/2596) were the most common locations. In cats, 53.5% (54/101) were domestic shorthairs, with a mean age of 11.1 years (range 1-18 years). The mean mass size was 2.4 cm in diameter (range 0.2-9 cm). The spleen (85.1%; 86/101) and liver (13.9%; 14/101) were the most common locations.