4-year-old, 1.4 kg castrated male ferret (Mustela putorius euro).The ferret presented for an approximately 2-month history of difficulty ambulating, progressive ataxia, and proprioceptive deficits in all limbs. MRI and CT identified a non-resectable mass at the level of C1 to C2. Fine needle aspirational cytology was performed. The animal was euthanized approximately 2 months later after failing to improve neurologically after attempting definitive radiation therapy.
An approximately 2 x 1.8 x 1 cm, multi-nodular, clear and gelatinous to hard and white mass effaced the C1 vertebra, extended ventrally into the cervical musculature and projected dorsally into the spinal canal and extended cranially into the foramen magnum along the ventral aspect of the brainstem. There was marked, segmental compression of the cervical spinal cord and brainstem.
Cytologic Description: Fine needle aspirate, cervical mass: The sample is of good quality with minimal hemodilution. There are moderate numbers of nucleated cells on a moderately thick, grainy, eosinophilic background. Nucleated cells are present individually or in small clusters, showing marked (up to 5-fold) anisocytosis. The smaller cells are approximately 10 microns in diameter with a small amount of basophilic cytoplasm. The larger cells (physaliphorous cells) are markedly distended up to approximately 80 microns by cytoplasmic vacuolation that is clear or contains pink, grainy material. Nuclei are round to oval and often eccentric, with reticular chromatin, typically lacking obvious nucleoli. Mitotic figures are not observed.
Cervical mass: Chordoma.
The chordoma was confirmed by histopathology and immunohistochemistry following postmortem examination. Histopathology revealed an unencapsulated, multilobulated, moderately cellular neoplasm that effaced the first cervical vertebra and was composed of polygonal cells arranged in solid sheets supported by a moderate amount of fibrous to myxomatous to chondromatous stroma. These cells were often markedly vacuolated, typical of the physaliphorous cells described in chordomas. No mitoses were observed. Immunohistochemistry for cytokeratin and vimentin expression was performed on decalcified sections of the neoplasm, resulting in weak to moderate, patchy, cytoplasmic expression of both markers.
Chordomas are the most common neoplasm of the musculoskeletal system of the ferret,(4) but have also been described in other species, such as rats,(11) cats,(2) humans,(10) mink(6) and dogs.(8) The embryonic notochord degenerates early in fetal development and remains as the nucleus pulposus within intervertebral disks.(7) In some cases, residual notochord cells remain outside the intervertebral disks and may become a chordoma.
In ferrets, chordomas arise primarily in or adjacent to the caudal vertebra,(4) but they also have been described elsewhere along the spine.(9,12) Chordomas are locally aggressive, destroy the vertebral body, and invade adjacent tissues. Cutaneous metastases of chordomas have been reported in ferrets.(7,12) Although chordomas of the tail may be treated by amputation, at other locations along the axial skeleton, chordomas may not be amenable to surgical therapy and can cause spinal cord compression, as seen in this case.
The main differential diagnosis for a chordoma is chondrosarcoma. The large, severely vacuolated, physaliphorous cells of chordomas are not a feature of chondrosarcoma;(8) however, differentiation of these tumors is further aided by immunohistochemistry. Chordomas express vimentin, cytokeratin, and S-100 protein, while chondrosarcomas do not express cytokeratin. Combining the midline location of the tumor, cytological criteria such as physaliphorous cells, and immunohistochemical expression of cytokeratin confirms a diagnosis of chordoma.
Cervical vertebrae: Chordoma.
Chordomas are fairly well described in humans; however, they are rare in domestic animals, with the exception of ferrets.(9) In both humans and rats, chordomas are more common in aged males.(2,11) In humans they can occur anywhere along the vertebral column, often extend into soft tissue, and are divided into three types: conventional, chondroid and dedifferentiated.(3) Conventional chordomas are slow-growing, but locally invasive with a high rate of recurrence, especially in those that arise from the sacrococcygeal region or the vertebrae. Chondroid chordomas tend to originate from the spheno-occipital region and generally behave more benignly.(1) Conversely, dedifferentiated chordomas are rare (less than 5% of cases), with histologic features of a high-grade spindle cell sarcoma and aggressive biologic behavior. The distinction between conventional, chondroid and dedifferentiated types is important prognostically as survival rates are up to three times higher with chondroid chordomas.(3)
Conference participants briefly discussed the occurrence of chordomas in various veterinary species. In ferrets, the most common location is on the tip of the tail; however, in most domestic species, chordomas tend to occur in the sacrococcygeal and cervical regions. In dogs, chordomas have also been reported in the brain, spinal cord, and skin.(5) Of the two reported cases of feline chordoma, one was initially diagnosed as chronic granulomatous inflammation due to the interpretation of the characteristic physaliphorous cells as atypical, foamy macrophages, but was later shown to be a classic chordoma, which subsequently metastasized to multiple lymph nodes.(2) The second feline case was classified histologically and immunohistochemically as a chondroid chroma.(1) Chondroid chordomas similar to the human subtype have been reported in ferrets, mink, cats and dogs.(1,5) Similarly to human medicine, the distinction between conventional and chondroid chordomas may also have some degree of prognostic significance in animals. Although all chordomas are potentially locally invasive, chondroid chordomas in ferrets, dogs and cats have not been reported to metastasize, while conventional chordomas in rats(11) and cats(2) (but not dogs)(5) seem to have a higher rate of metastasis. Additionally, chordomas arising from the tail appear to have a good prognosis in all cases.(1)
An alternate spelling of physaliferous may be seen in the literature, and is considered a correct spelling as well.
1. Carminato A, Marchioro W, Melchiotti E, Vascellari M, Mutinelli F. A Case of coccygeal chondroid chordoma in a cat: morphological and immunohistochemical features. J Vet Diagn Invest. 2008;20(5):679-681.
2. Carpenter JL, Stein BS, King NW Jr, Dayal YD, Moore FM. Chordoma in a cat. J Am Vet Med Assoc. 1990;197:240-242.
3. Chugh R, Tawbi H, Lucas DR, et al. Chordoma: the nonsarcoma primary bone tumor. The Oncologist. 2007;12(11):1344-1350.
4. Dunn DG, Harris RK, Meis JM, Sweet DE. A histomorphologic and immunohistochemical study of chordoma in twenty ferrets (Mustela putorius furo). Vet Pathol. 1991;28(6):467-473.
5. Gruber A, Kneissi S, Vidoni B, Url A. Cervical spinal chordoma with chondromatous component in an dog. Vet Pathol. 2008;45(5):650653.
6. Hadlow WJ. Vertebral chordoma in two ranch mink. Vet Pathol. 1984;21(5):533-536.
7. Munday JS, Brown CA, Richey LJ. Suspected metastatic coccygeal chordoma in a ferret (Mustela putorius furo). J Vet Diagn Invest. 2004;16(5):454-458.
8. Munday JS, Brown CA, Weiss R. Coccygeal chordoma in a dog. J Vet Diagn Invest. 2003;15(3):285-288.
9. Pye GW, Bennett RA, Roberts GD, Terrell SP. Thoracic vertebral chordoma in a domestic ferret (Mustela putorius furo). J Zoo Wildl Med. 2000;31(1):107-111.
10. Rich TA, Schiller A, Suit HD, Mankin HJ. Clinical and pathologic review of 48 cases of chroma. Cancer. 1985;56(1):182-187.
11. Stefanski SA, Elwell MR, Mitsumori K, Yoshitomi K, Dittrich K, Giles HD. Chordomas in Fischer 344 rats. Vet Pathol. 1988;25(1):42-47.
12. Williams BH, Eighmy JJ, Berbert MH, Dunn DG. Cervical chordoma in two ferrets (Mustela putorius furo). Vet Pathol. 1993;30(3):204-206.