History
An 11-year-old 21-kg (46-lb) female Staffordshire Bull Terrier from a local animal shelter was evaluated at the Veterinary Clinic Rostock because of lip smacking and hypersalivation.
Clinical and Gross Findings
Examination of the oral cavity revealed a single, circumscribed, pedunculated mass within the oral mucosa of the frenulum linguae. The mass was clearly defined against other structures of the oral cavity. A CBC revealed no abnormalities. The dog was anesthetized and the entire mass was excised. Gross inspection revealed a 2-cm-diameter spherical mass, which on cut-section was tan with multiple, yellow, soft, fatty areas admixed with rare, glistening, white, firm cartilaginous foci and covered by intact oral mucosa (Figure 1). The excised mass was fixed in neutral-buffered 10% formalin and sent to the Department of Pathology, University of Veterinary Medicine Hannover, for histologic examination.
Photograph of a formalin-fixed cross section of a pedunculated mass excised from the oral mucosa of the frenulum linguae of an 11-year-old Staffordshire Bull Terrier that was evaluated because of lip smacking and hypersalivation. Notice the tan, solid, collagen fiber–rich cut surface with multiple yellow, soft, fatty areas and rare, white, glistening, firm cartilaginous foci.
Citation: Journal of the American Veterinary Medical Association 251, 10; 10.2460/javma.251.10.1157
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Histopathologic Findings
Histologic examination of the submitted tissue revealed a circumscribed, nonencapsulated, expansile, round, pedunculated, poorly cellular mass within the lamina propria. The excised mass had complete margins; it was covered by oral squamous mucosa and consisted of 3 intermixed fibroblastic, lipomatous, and cartilaginous components (Figure 2). Two-thirds of the mass was formed by haphazardly arranged bundles and streams of spindloid cells within a prominent collagen fiber–rich stroma. The fibroblast-like, spindloid cells had indistinct cellular borders, low amounts of eosinophilic cytoplasm, and oval to elongated, moderately heterochromatic nuclei. Furthermore, approximately 30% of the cross-sectional area had a regionally variable number of interspersed, poorly demarcated, coalescing nests of well-differentiated adipocytes; approximately 5% of the cross-sectional area was composed of oligofocal, well-demarcated foci of cartilage. All 3 components of the mass had low to moderate anisocytosis and anisokaryosis. Mitoses were rarely seen, with a mitotic index of ≤ 1 mitotic figure/10 hpf (400×). The presence of collagen fibers, lipid within adipocytes, and cartilage matrix was confirmed by use of azan, oil red-O, and Alcian blue stains, respectively.
Photomicrographs of sections of the excised oral mass from the dog in Figure 1. A—The nonencapsulated, expansile, poorly cellular mass is composed of intermixed collagenous, lipomatous, and cartilaginous components. H&E; bar = 200 μm. B—At a higher magnification, notice the regionally variable number of nests of well-differentiated adipocytic cells. H&E stain; bar = 50 μm. C—The mass contains oligofocal, well-demarcated foci of cartilage. H&E stain; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 251, 10; 10.2460/javma.251.10.1157
Immunohistochemical analyses were performed with a panel of primary antibodies directed against vimentin (clone V9),a desmin (clone D33),a α-smooth muscle actin (clone 1A4),a cytokeratin (clone AE1/AE3),a melan A (clone A103),a factor VIII–related antigen (rabbit polyclonal antibody),a and S-100 protein (rabbit polyclonal antibody)b and use of the avidin-biotin-peroxidase complex methodc with 3,3′-diaminobenzidine-tetrahydrochloride as a chromogen.1 A high proportion of the fibroblastic, adipocytic, and chondrocytic neoplastic cells were positive for vimentin; a variable proportion of intermixed spindloid cells (suggested to be angiofibroblasts) and all vascular endothelial cells were positive for factor VIII–related antigen. Neoplastic cells were negative for desmin, α-smooth muscle actin, cytokeratin, melan A, and S-100 protein.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis and case summary: oral lipoma with fibromatous and chondroid metaplasia in a Staffordshire Bull Terrier.
Comments
For the dog of the present report, the main clinical differential diagnoses for a canine oral mass without gingival or boney involvement included melanoma, squamous cell carcinoma, fibrosarcoma, papilloma, extramedullary plasmacytoma, mast cell tumor, granular cell tumor, or a neuroendocrine tumor. Various granulomatous, eosinophilic, and proliferative inflammatory diseases2 were also included as differential diagnoses. However, the histopathologic features were indicative of a lipoma with fibromatous and chondroid metaplasia.
Reports of lipomas with fibromatous and chondroid metaplasia in dogs are rare,3 and the current veterinary World Health Organization classification lacks an appropriate category.4 In the past, some researchers have preferred the term benign mesenchymoma for tumors with comparable morphological characteristics in humans.5,6 Mesenchymomas are tumors composed of 2 or more mesenchymal components in addition to fibrous tissue.5,7 However, the use of the term mesenchymoma is discouraged in the current WHO classification of tumors of soft tissues in humans owing to the rather nonuniform clinicopathologic behavior of the various neoplasms meeting this definition.8 Therefore, in agreement with the previously published guideline that no single mesenchymal tissue should predominate in a benign mesenchymoma,3,6 a diagnosis of lipoma with fibromatous and chondroid metaplasia was made for the dog of the present report.
Considering the current knowledge of the multi-potency and definition of mesenchymal stem cells in the light of the cancer stem cell hypothesis9,10 as well as the occurrence of mesenchymal stem cells in canine adipose tisse,11 it seems reasonable to suggest that the different tissues within mixed mesenchymal tumors arise from a common cancer stem cell. With regard to a lipoma with fibromatous and chondroid metaplasia, currently unknown secondary exogenous triggers (eg, ischemia or mechanical stress) are needed to induce the fibromatous and chondroid differentiation. However, the discussion of whether this entity should be diagnosed as a lipoma with fibromatous and chondroid metaplasia or a benign mesenchymoma seems to be rather academic, and further studies are needed to clarify this point.
Given the rarity of reports of lipomas with fibromatous and chondroid metaplasia in dogs, information concerning the biological behavior of this tumor entity in this species is scarce.3 Furthermore, the use of commonly accepted guidelines for characterization of soft tissue sarcomas of the trunk and extremities is not appropriate because of the well-known aggressive behavior of well-differentiated oral sarcomas.4,12,13 However, in the case described in the present report, the mass had a well-circumscribed nature, low mitotic index, and absence of notable atypia, which supported the notion that it was a benign tumor. Anecdotally, the dog of the present report recovered from anesthesia and surgery within a few days; at a follow-up examination 2 years after surgery, there was no evidence of recurrence of the mass or signs of metastatic disease.
Acknowledgments
The authors thank Bettina Buck and Petra Grünig for technical assistance.
Footnotes
Dako, Hamburg, Germany.
Sigma Aldrich, Taufkirchen, Germany.
Elite PK6100, Vector Laboratories, Burlingame, Calif.
References
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