HORSES

Cutaneous angiomatosis (a.k.a. lymphangioma, lymphangiomatosis) in a young horse  

Murray Hazlett, Christina McKenzie, Rainee Stoddart, Luis G. Arroyo

A 3-y-old warmblood mare was presented with a history of intermittent swelling and discharge on the skin over the gluteal area, on both sides, mainly in the right side. The masses were 5-20 mm small soft skin bumps and were felt to be multilocular cysts that would periodically drain (Fig. 1A). The mare was biopsied on the farm.

The biopsy was diagnosed as a cutaneous lymphangioma (Figs. 1B, C). Because of the lack of blood present in the spaces, it was suspected these were lymphatic vessels. No mitotic figures were seen. Cellular pleomorphism was minimal. The horse was referred to the Ontario Veterinary College for additional workup and re-biopsy. The second biopsy was similar, with all layers of the dermis and the dense subcutaneous collagen, hair follicles, and dermal collagen separated by elongated, clear spaces lined by a single layer of inconspicuous endothelium and that wrapped around pre-existing collagen bundles resulting in a short branching pattern. Some lumina contained moderate numbers of red blood cells (interpreted as blood and/or lymphatic vessels). In the dermis, the clear spaces were mostly arranged parallel to hair follicles and extended to the epidermis. Endothelial cells lining these dilated vessels were flattened, with minimal cytoplasm and basophilic nuclei with inconspicuous nucleoli, and they stained positive for factor VIII (Fig. 1D) – an endothelial cell marker. No mitotic figures were seen.

Nomenclature used for this lesion varies in the literature, usually referring to equine cutaneous lymphangioma. It is questionable as to whether lymphangiomas are “true” neoplasms or hamartomas, i.e. a tumour-like proliferative disease originating from altered fetal development of the lymphatic system. Lymphangiomas occur predominantly at locations where the lymphatic system develops primitive lymph sacs – the jugular and inguinal lymph sacs, existing in pairs, and the retroperitoneal lymph sac and the cisterna chyli* (Bachmann and Worm 1967). This would explain the common distribution of these lesions in humans, where they are better documented, on the neck, axilla, retroperitoneal tissue, thighs and inguinal regions. It would also explain the bilateral distribution of the lesions seen in this horse. Fetal tissue growth and changes may result in isolated non-communicating lymphatic tissue that proliferates. Therefore, this neoplasia is observed predominantly in young individuals.¹

The horse was not treated and treatment regimens are currently being decided.   AHL

*Much of this work was originally done by Florence R Sabin M.D. published in 1902 – in Developmental Dynamics, Vol 1, May 1902. This meticulous work has held up for > 100 years. Dr Sabin was the first woman to hold a full professorship at Johns Hopkins School of Medicine, the first woman elected to the National Academy of Sciences, and the first woman to head a department at the Rockefeller Institute for Medical Research.

Reference

1. Gehlen H, Wohlsein P. Cutaneous lymphangioma in a young Standardbred mare. Equine Vet J 2000;32:86-88.

Figure 1. A. Gross photograph of the lesion – lumpy area on the hip region (arrow). B. Full-thickness biopsy showing vessels in the superficial and deep areas of the vessel (arrows). C. Close view of vessels in the deep layers of the biopsy. D. Factor VIII IHC stain shows red staining of cells lining the vessels compatible with vascular or lymphatic endothelium.