EXPRESS: First clinical report of a feline intraosseous myelolipoma

Case series summary A 7 year-old neutered male Domestic Shorthair cat was presented with a firm, painless mass palpated over the right iliac region. CT imaging revealed a well-demarcated monostotic lesion within the right iliac wing, composed of fat and soft tissue attenuation. The lesion caused cortical thinning, irregularity, and partial interruption, without any periosteal reaction or surrounding inflammation, findings suggestive of a benign process. Based on these imaging features and the lesion’s anatomical location, a partial iliectomy with preservation of the pelvic limb was performed. The mass was excised en bloc. Histopathological evaluation confirmed the diagnosis of intraosseous myelolipoma, characterized by a well-delineated proliferation of mature adipose tissue intermingled with trilineage hematopoietic elements (myeloid, erythroid, and megakaryocytic), without cytological atypia or malignant features. At the 15-day and 2-month follow-ups, the cat walked normally and had returned to its usual activities. Limb function remained intact. Relevance and novel information Intraosseous myelolipomas are exceptionally rare in both human and veterinary medicine, and to the authors’ knowledge, this is the first case described in a feline patient. Diagnosis requires advanced imaging and histopathological confirmation. Surgical excision by partial iliectomy enabled complete removal of the lesion while preserving limb function, resulting in favourable short-term clinical outcome. This case expands the range of differential diagnoses for feline pelvic bone lesions and highlights the feasibility of conservative, limb-sparing surgical techniques in select cases.