6-year-old male Basset HoundThere was a 3.5 x 3.5 x 1cm raised, red, ulcerated subcutaneous nodule on the right dorsal elbow. The lesion had been present for months, and was removed because it limited the range of motion of the elbow.
The superficial and deep dermis contains multiple cystic structures that occasionally compress or displace adnexal structures.Â The cysts are lined by a stratified squamous epithelium.Â The basal layer of the epithelium frequently forms short rete pegs that extend into the surrounding dermal collagen.Â There is extensive luminal acantholysis of the stratum spinosum, with frequent cleft formation.Â There are dyskeratotic/apoptotic keratinocytes within the stratum spinosum and acantholytic cells within the clefts or within the cyst lumen, which also contains abundant keratin (Fig 1-1).Â Some cysts contain large numbers of neutrophils and there are multiple foci of mineralization of the luminal debris.Â Cysts are surrounded by varying degrees of dermal fibrosis.Â Moderate numbers of lymphocytes, plasma cells and histiocytes surround some of the cysts, as well as surround blood vessels in the deep dermis.
In some sections there is rupture of the cyst wall with release of acantholytic cells and keratin debris into the dermis.Â A mild infiltrate of neutrophils and epitheloid macrophages surround these areas.
Skin: Warty dyskeratoma
Warty dyskeratomas were first described and named in humans.Â The first and only report in the veterinary literature is of warty dyskeratomas arising in 2 dogs.(1) There are not enough reports to comment on age, breed or location predispositions.Â In our database from 2004 to present, there are three warty dyskeratomas (including the present case).Â Two of these tumors were in Bassett Hounds and one was in a Yorkshire Terrier.Â Dogs ranged in age from 8 months to 14 years.Â The case described here was on the right elbow, while the other two cases arose on the right hip or thigh.Â Lesions ranged in size from 3 to 13cm.Â
Warty dyskeratomas are rare benign tumors that are believed to arise from hair follicles.Â Histologically there are single to multiple cystic structures in the dermis that are lined by a stratified squamous epithelium that is hyperplastic and forms rete pegs that extend into the surrounding dermis.Â There is acantholysis of the stratum spinosum which can result in separation of the superficial layers of epithelium from the basal layers.Â There is frequent keratinocyte apoptosis or dyskeratosis.Â The cyst lumen is usually filled with keratin debris and acantholytic cells.Â Secondary inflammation from release of cyst contents into the surrounding dermis is common.(2)
Haired skin: Warty dyskeratoma
Dr.Â Goldschmidt stated he has seen just a few of these over the last twenty years at the University of Pennsylvania, and this entity seems to be very rare in domestic animals.
Warty dyskeratomas in animals can be confused with an acantholytic variant of squamous cell carcinoma originating from the hair follicle.Â Squamous cell carcinomas often have extensive apoptosis as a distinguishing feature.Â Warty dyskeratomas are benign tumors and do not infiltrate through the basement membrane.(1)
In humans, warty dykeratomas are solitary verrucous epidermal neoplasms with marked acantholysis and dyskeratosis of proliferating neoplastic cells.(3) In humans, these tumors generally are found on sun-exposed body parts, and these lesions usually involve hair follicles with some reported cases of oral involvement.Â Tumors appear as single, raised nodules with umbilicated centers and are usually benign tumors.Â Histologically, these masses are endophytic with densely packed keratin and suprabasilar clefts with marked acantholysis.Â Acantholytic cells are described as either corps ronds, which are suprabasilarly located, large, eosinophilic, rounded cells with perinuclear halos, or corps grains, which are small intensely eosinophilic, ovoid cells with pyknotic flattened nuclei.Â These two types of cells are often adjacent to an acantholytic stratum granulosum and parakeratotic stratum corneum.(3)
1.Â Gross TL, Ihrke PJ, Walder EJ, Affolter VK: Skin Disease of the Dog and Cat: Clinical and Histopathologic Diagnosis.Â 2nd ed., pp 612-614.Â Blackwell Science, Denmark, 2005
2.Â Hill, JR: Warty dyskeratoma in two dogs.Â In: Proceedings of the 3rd AAVD/ACVD Meeting, Phoenix, (1987) p.40.Â
3.Â Murphy GR, Elder DE: Atlas of Tumor Pathology, Non-Melanocytic Tumors of the Skin, 3rd Series, vol 1, pp.Â 27-28.Â Armed Forces Institute of Pathology, Washington DC, 1991