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Myelolipoma and angiomyolipoma are rare benign mesenchymal tumors in animals. In dogs and cats, they most commonly occur in the spleen and adrenal glands; however, a few existing studies also report several other localizations. Their clinical significance lies mainly in the context of differential diagnosis, as they may be mistaken for malignant tumors on imaging studies.

Our retrospective study aimed to collect and analyze histologically confirmed cases between 2020 and 2024.

Our cases were obtained from the records of the Mátrix Veterinary Histopathology Laboratory. During the 4-year study period, a total of 78 animals were diagnosed with myelolipoma (67 dogs, six cats, three cheetahs, and one each of ferret and guinea pig), while angiomyolipoma was diagnosed in an additional three dogs.

Of the 67 dogs with myelolipoma, 25% were mixed-breed (17 dogs), 15% Dachshunds (10 dogs), 13% Hungarian Vizslas (9 dogs), 7% German Shepherds and Staffordshire Terriers each (5–5 dogs), 4% French Bulldogs (3 dogs), and 3% Beagles, Labradors, and Golden Retrievers each (2–2 dogs). The median age of affected dogs was 12 years (range, 1.8–16 years; interquartile range, 2 years), and 61% of the dogs were female. In 97% of canine cases (65 cases), the lesion was detected in splenic samples. Two dogs had exclusively extra-splenic samples, one dog was diagnosed with myelolipoma in the liver, while in another case, the lesion was identified in the stomach wall, pancreas, and omentum. Concomitant malignant tumors were observed in 15% of the dogs (10 cases): hemangiosarcoma, histiocytic sarcoma, and lymphoma in the spleen, and hemangiosarcoma, soft tissue sarcoma, carcinoma, and melanoma outside the spleen. In the other species, myelolipomas were detected exclusively in the spleen. The three angiomyolipomas, however, were identified in subcutaneous connective tissue, retroperitoneum, and ovary.

We performed a more detailed evaluation of 16 dogs and one ferret diagnosed with myelolipoma, including a review of their case histories and survival times. Based on available descriptions (13 cases), the lesion size ranged from pinhead-sized to the size of a small child’s head. In all cases with known follow-up, survival time exceeded 6 months, and no recurrence was reported.

Based on our findings, the vast majority of histologically examined myelolipomas originate from the spleen. Certain breeds (e.g., Dachshund, Vizsla, German Shepherd) and female dogs appear to be predisposed to this condition. In most cases, no malignant lesions are detected either in the spleen or other organs, although myelolipoma may occasionally occur concurrently with malignant processes of the spleen or other organs. Recognition of this lesion is crucial for the accurate interpretation of imaging studies and for establishing the correct differential diagnosis.