Cutaneous Lymphosarcoma
Stephen D. White
Equine Lymphoma
Cutaneous lymphoma has occasionally been reported in horses.1-8 Both T-cell and B-cell forms have been reported.9,10 Lesions present as either cutaneous or subcutaneous nodules.
Diagnosis is made by biopsy and, ideally, immunohistochemistry to determine cell type.7,8 In one horse, progesterone receptors were demonstrated on the lymphoma (B) cells, and the lesions regressed after removal of an estrogen-secreting ovarian tumor.4 This horse also had a history of partial regression of its tumor after administration of a synthetic progestin, altrenogest (0.044 mg/kg PO once daily for 10 days). Another horse demonstrated reduction in tumor size after administration of another synthetic progestogen, megestrol acetate (0.2 mg/ kg PO once daily for 8 days), as well as a local injection of 20 mg betamethasone into a mass.5 Clearly, treatment is far from standardized, but the progesterone drugs may offer a reasonable treatment modality. Lymphosarcoma is discussed in Chapter 37.Bovine Lymphoma
Cattle occasionally are affected by cutaneous lymphoma. The presentation is multifocal intracutaneous nodules, often accompanied by alopecia. Lymphadenopathy, leukocytosis, and lymphocytosis are often present, and internal organs may be affected.11 The juvenile form is not necessarily associated with the bovine leukemia virus (BLV) and is of T-cell origin.12
Ovine Lymphoma
There are rare reports of cutaneous lymphoma in sheep.13,14
Cysts
Stephen D. White
Cutaneous cysts are benign lesions characterized by an epithelial wall with keratinous contents. Cutaneous cysts are subdivided into several types based on their histopathologic features.
Epidermal Cysts
Among large animals, epidermal cysts have been reported in horses,1 cattle,2 and sheep.3 These cysts may be more properly called follicular cysts because the epithelial lining is probably most often derived from the follicular epithelium rather than the epidermis.
The cysts can be found anywhere on the body, single or multiple, congenital or acquired, and generally range in size from 0.2 to 3 cm in diameter. The cysts are covered by intact epithelium and generally do not attach to the overlying epidermis. Microscopically, epidermal cysts consist of a wall of stratified squamous epithelium surrounding a keratin-filled lumen. Epidermal appendages are not associated with the cyst wall, a feature that distinguishes epidermal from dermoid cysts.Epidermal cysts are thought to originate from occlusion of a hair follicle or by traumatic implantation of the epidermis. A tentative diagnosis may be made by performing fine-needle aspiration of a lesion and obtaining a fluid that is clear to brownish in color. Aspiration of the contents may temporarily decrease the size of the cyst, but it typically refills. Definitive diagnosis is made by excisional biopsy, which is curative. Epidermal cysts are benign lesions, although painful inflammatory responses and ulceration may result if the cyst is ruptured, with extrusion of contents into the adjacent dermis and subcutis.
Dermoid Cysts
Dermoid cysts are very similar clinically to epidermal cysts but are much less common. Among large animals, they have been identified in horses,1 goats,4 and cattle.5 In cattle, dermoid cysts may be congenital, have been reported to be as large as 10 cm (4 inches) in diameter, and are said to develop most frequently over the cranial area of the thorax5 and in the pharyngeal region. In horses, dermoid cysts may be single or multiple and are observed most frequently along the dorsal midline between the withers and the croup. Dermoid cysts are believed to result from displacement of embryonic cells into the subcutaneous tissue. They can be distinguished histologically from epidermal cysts by the presence of epidermal appendages within the wall of the cyst and by a lumen that often contains hair and secretions from sebaceous and sweat glands in addition to keratin.
As with epidermal cysts, surgical excision is diagnostic and curative.Dentigerous Cysts
Dentigerous cysts are a congenital defect recognized in horses and are believed to be the result of an abnormality of the first branchial cleft.6 Clinically, a unilateral saclike swelling that contains embryonic teeth is seen at the base of the ear. The lesion may be firmly attached to the concheal cartilage or temporal bone. Dentigerous cysts tend to fistulate. Treatment consists of surgical excision.6 Dentigerous cysts have also been reported in sheep and are suspected of being related to a nutritional deficiency of copper.7
Wattle Cysts
Wattle cysts are found in goats and usually are present at the base of the wattle. Nubians and Nubian crossbreeds may be predisposed to developing these cysts. The cysts are congenital, but they may not be apparent until the animal is several months old. Tentative diagnosis is based on aspiration of clear fluid, which will temporarily decrease the size of the cyst. Surgical excision is diagnostic and curative. Histologic examination reveals a cyst wall composed of one or two layers of cuboidal to columnar epithelial cells. The cyst cavity contains homogeneous, amorphous basophilic substances.7