In dogs and cats, angiolipomas are typically small discrete masses located in the subcutis of the thorax [3
]. In humans favored sites include both the thorax and extremities [10
]. Infiltrative angiolipomas in humans may have a predisposition for localization in the neck [11
]. Angiolipomas are defined histologically by neoplastic blood vessels mixed with mature adipose tissue [2
]. Mitotic figures are rare or absent in both the endothelial and adipocyte population, and features of malignancy are lacking. Fibrin thrombi may be evident within vascular channels.
The angiolipoma described in this case was located on the thorax and was comprised of thin walled vascular channels lined by well differentiated endothelial cells and supported by lobules of well-differentiated adipose. Unlike angiolipomas described in other species, which are typically discretely marginated, the mass in this case invaded the deep cutaneous musculature, resulting in mild myocyte degeneration and loss. Importantly, invasive angiolipomas may be difficult to distinguish from intramuscular hemangiomas, which in humans and other species are represented by primary development of a cavernous vascular neoplasm within skeletal muscle, often accompanied by abundant adipose tissue [12
]. In this case, the majority of the mass effect was restricted to the dermis and subcutis and the lesion was interpreted as secondarily invading adjacent muscle, rather than originating within it.
Cutaneous neoplasms are uncommon in goats in general. Reported cutaneous neoplasms in goats include squamous cell carcinoma, squamous papilloma, epithelioma, apocrine sweat gland adenoma, fibroma, melanoma, mast cell tumor, histiocytoma, hemangioma, and hemangiosarcoma [10
]. As in other species, factors such as breed, genetics, coat and skin color, and environment likely contribute to oncogenesis in caprine skin. Unfortunately, specific oncogenic factors have not been well studied in goats. As reported in other species, caprine cutaneous tumors often arise in lightly pigmented breeds or in areas of white or lightly pigmented hair, suggesting that UV radiation may play a role in oncogenesis [15
]. Compatible with this predisposition, the patient in this report was lightly colored, though the direct relationship between UV exposure and the lesion in this case is uncertain, since actinic changes were not identified in the adjacent or marginal skin tissue. Also intriguing is the patient's history as a pack animal and the location of the lesion in the pack saddle area. Chronic inflammation has also been associated with development of cancer in several species, presumably due to the long-term effects of locally produced cytokines and growth factors intended to stimulate growth for healing purposes. For example, chronic corneal inflammation can lead to secondary corneal neoplasia in dogs, and chronic inflammatory bowel disease in cats is a well-recognized risk factor for intestinal lymphoma [19
]. Additionally, cutaneous papillomas and squamous cell carcinomas have been reported to develop in cattle at sites of traumatic freeze and heat branding [21
]. The tumor in the patient reported here may have arisen under the influences of chronic irritation and inflammation associated with tack.
Other differentials considered for nonpruritic crusting lesions in small ruminants include hyperkeratosis secondary to trauma, dermatophilosis, staphylococcal dermatitis, zinc deficiency, pemphigus foliaceus, and ringworm (Trichophyton verrucosum
and Epidermophyton floccosum
]. Close evaluation of the biopsied material allowed rejection of these inflammatory conditions. Squamous cell carcinoma was considered based on gross appearance but was not supported by the histological findings. Hemangioma was considered because of the benign appearance of the endothelial cells, and hemangiosarcoma was considered because of the infiltrative nature of the lesion. Ultimately, infiltrative hemangiolipoma was considered the most appropriate diagnosis because of the relative monotony of the neoplastic population, lack of atypical features, low mitotic rate, invasion of deep muscle, and close association of neoplastic vessels with mature lobules of adipose tissue.
Human and canine angiolipomas are considered benign neoplasms and surgical excision is curative [3
]. Minimal data is available for this tumor type in other species, but benignancy is likely a consistent feature. The biologic behavior of this lesion in a goat is uncertain, but the degree of invasiveness suggests that clinical followup is warranted and that local recurrence may occur, particularly given incomplete excision.