JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2681629): Adult boa constrictor (Boa constrictor constrictor)
HISTORY: A 1 cm diameter skin mass that recurred after surgical excision
HISTOPATHOLOGIC DESCRIPTION: Skin: Expanding the dermis and elevating the multifocally ulcerated epidermis is a 2 x 1.5 cm unencapsulated, multilobulated, infiltrative, pigmented neoplasm. Neoplastic cells are polygonal to spindle and arranged in nests and packets on a fine fibrovascular stroma; neoplastic cells frequently spindle forming interlacing bundles, short streams and whorls. Cells have indistinct borders, a moderate amount of eosinophilic granular cytoplasm with variable amounts of gold-brown to green granular, birefringent pigment, an oval to elongate nucleus with coarsely clumped chromatin and variably distinct nucleoli. Mitoses average 3 per HPF. Rarely, small nests of neoplastic cells extend into the epidermis (junctional activity). Vessels within the neoplasm are surrounded by variable numbers of lymphocytes, plasma cells, histiocytes and granulocytes. There is a focally extensive area of ulceration with granulation tissue in the underlying dermis and epidermal hyperplasia with hyperkeratosis in the adjacent epidermis.
MORPHOLOGIC DIAGNOSIS: Skin: Iridophoroma, malignant, Boa constrictor (Boa constrictor constrictor), reptile.
- Rare neoplasm of reptiles most commonly reported in snakes; composed of chromatophores (contractile pigmented cells of neurectodermal origin)
- Snake skin contains three classes of pigment producing cells; tumors are classified according to the type of chromatophores they contain:
- Melanophores- dark brown to black melanin-producing cells (melanophoroma or melanoma)
- Xanthophores reddish carotenoid and pteridine producing cells (xanthophoroma)
- Iridophores - crystalline purine-producing cells containing refractile (birefringent) granules of guanine, adenine, hypoxanthine, or uric acid (iridophoromas)
- Pigment cells are controlled by hormonal or neurologic processes or a combination of the two
- Chromatophores are best differentiated ultrastructurally:
- Melanophores contain amorphous granules
- Xanthophores contain concentric lamellae (pteridines)
- Iridophores contain crystals ("reflecting platelets")
- Mosaic pigment cells contain two or more types of pigment organelles
- Neoplasms from all four classes have been reported in snakes
TYPICAL CLINICAL FINDINGS:
- Presents as ulcers or blisters on the skin
- Underlying mass is often firmly attached
TYPICAL GROSS FINDINGS:
- Subcutaneous nodules with overlying ulceration
- Occasionally overlying integument is hyperkeratotic
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Pleomorphic population of cells with abundant brown to gold pigment
- In unstained electron microscopy - presence of variably sized granules which are cytoplasmic lined "reflecting platelets"
- Composed of guanine crystals which are usually lost during processing; arise from the endoplasmic reticulum and Golgi complex
- Forms a latticework of empty elliptical membranes
ADDITIONAL DIAGNOSTIC TESTS:
- S-100 protein
- PNL-2 – although less sensitive than S-100
- Electron microscopy
- The sensitivity of melan A and HMB45 is low in reptile melanocytic tumors.
- Granulomas due to bacteria, fungi, trauma, or septicemia
- Parasitic masses due to plerocercoids, larval dracunculids, acanthocephalans or spirurids
- Other neoplasms: Fibrosarcoma, squamous cell carcinoma, melanoma
- Melanophoroma: Amorphous granular melanin granules (melanosome)
- Mosaic chromatophoroma: Combined contractile pigment granules
- Xanthophoroma: Concentric lamellar pteridines (Pterinosome)
- Chromatophoromas have been reported in a variety of snakes
- Recent Vet Path article outlining retrospective study on captive snakes stated that most commonly affected snakes are colubrids with the San Francisco garter snake the most commonly affected species.
- Reported in several fish species
- Reported in dwarf bearded dragon (Pogona Henrylawsoni)
- Catao-Dias JL, Nichols DK. Neoplasia in snakes at the National Zoological Park, Washington DC (1978-1997). J Comp Path. 1999;120:89-95.
- Cheville NF. Ultrastructural Pathology: An Introduction to Interpretation. 2nd Ames, IA: Iowa State University Press;2009:815.
- De Brot S, Sydler T, Nufer L, Ruetten M. Histologic, immunohistochemical, and electron microscopic characterization of a malignant iridophoroma in a dwarf bearded dragon (Pogona Henrylawsoni). J Zoo Wildl Med. 2013; 46(3):583-587.
- Frye FL. Reptile Care: An Atlas of Diseases and Treatments. Vol 1. Neptune City, NJ:THF Publications, Inc;1991:473-511.
- Gregory CR, Harmon BG, Lattimer KS, Campagnoli RP, McManamon RM, Steffens WL. Malignant chromatophoroma in a canebrake rattlesnake (Crotalus horridus atricaudatus). J Zoo Wildl Med. 1997;28(2):198-203.
- Heckers KO, Aupperle H, Schmidt V, Pees M. Melanophoromas and iridophoromas in reptiles. J Comp Path. 2012;146:258-268.
- Munoz-Gutierrez JF, Garner MM, Kiupel M. Cutaneous chromatophoromas in captive snakes. Vet Pathol. 2016; 53(6):1213-1219.
- Okihiro MS: Chromatophoromas in two species of Hawaiian butterfly fish, Chaetodon multicinctus and miliaris. Vet Pathol. 1988;25:422-431.