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Nine-year-old castrated male mixed breed dog presented to the Dentistry and Oral surgery Service for further evaluation of an oral mass and oronasal fistula. Biopsy 1 week prior indicated chronic active fibrosing stomatitis with spindle cell atypia.

CT of the head (bone precontrast, soft tissue post-contrast). The patient’s left is left on the image.

Intraoral examination

CT of the head, bone window.
The patient's left is left on the image.

Soft tissue window post-contrast.
The patient's left is left on the image.

  • From the level of the left maxillary 2nd premolar tooth, there is marked moth-eaten lysis of the rostral left maxilla and hard palate of the maxillary and palatine bone that extends caudally with worsening complete lysis of the caudal hard palate. The lysis crosses midline and involves patchy to complete lysis of the right caudal maxilla at the level of the caudal molar teeth. There is a large oronasal fistula/ cavity along the medial aspect of the left maxillary molar teeth with complete loss of regional turbinates. There is severe lysis of the osseous structures (frontal bone, lacrimal bone, palatine bone) associated with the medial aspect of the left globe. There is lysis of the left rostroventral cribriform plate. The presphenoid and rostral basisphenoid bones are heterogeneous with ill-defined medullary lysis.
  • There is marked amount of variably heterogeneously contrast enhancing material within the left nasal passage that extends from the level of the maxillary canine tooth caudally to the described oronasal fistula and along the ventromedial aspect of the left eye. Heterogeneous soft tissue attenuation extends further caudally to the level of the left pterygoid musculature. The left eye and periorbital soft tissue structures are dorsally and slightly laterally displaced.
  • There is no contrast enhancement of the meninges or frontal lobes of the brain in the area of cribriform plate lysis.
  • There is mild atrophy of the left masticatory musculature.
  • The mandibular lymph nodes are prominent (left worse than right). The medial retropharyngeal lymph node is mildly enlarged.


Aggressive left nasomaxillary/orbital mass lesion with lysis of multiple osseous structures including the cribriform plate. Findings are most consistent with neoplasia and severe destructive rhinitis +/- concurrent osteomyelitis. Considering the biopsy results, findings may be consistent with “histologically low-grade, yet biologically high-grade fibrosarcoma”. Other forms of neoplasia cannot be ruled out. Consider rebiopsy of a region with a more soft tissue attenuating component.

Mild mandibular lymphadenopathy (left worse than right) and mild medial retropharyngeal lymphadenopathy may be reactive vs. metastatic.

Left masticatory muscle atrophy. Findings may be attributable to “reflex sympathetic dystrophy” considering the lack of visible involvement of the described mass with the region of the left trigeminal nerve or foramen ovale. Other possibilities include chronic masticatory myositis vs. trigeminal neuritis vs. mass effect causing trigeminal nerve compression cannot be ruled out.

The dog was suspected to have “histologically low-grade, yet biologically high-grade fibrosarcoma”. Based off the aggressive appearance of the mass from the CT study and the anticipated poor prognosis, the patient was humanely euthanized.

Biopsy results:

Microscopic description: The submitted tissue is composed of 2 tissue pieces of oral mucosa and submucosa from one site. Both tissue pieces contain a similar deep inflammatory process. The submucosa is effaced by organizing atypical fibroplasia associated with moderately dense inflammatory infiltrates. Infiltrates consist of neutrophils admixed with lymphocytes, plasma cells and reactive macrophages. The fibroblastic spindle cells are arranged in interlacing streams within a moderately vascularized stroma. Individual spindle cells have large ovoid nuclei, prominent nucleoli and moderate amounts of eosinophilic cytoplasm. There is moderate cellularity. Occasional mitotic activity is identified.

Microscopic findings: Severe chronic active and fibrosing stomatitis with spindle cell atypia

Comment: The submitted tissue has evidence of a severe chronic and proliferative inflammatory process. Inflammation is associated with fibroplasia which has a moderate degree of atypia. A reactive fibroblastic process may be possible. However, continued clinical monitoring is advised to rule out some other underlying condition, such as inflamed neoplasia.


Histologically low-grade, yet biologically high-grade fibrosarcoma(1) has been characterized by an innocuous histologic appearance, but have aggressive biologic behavior evidenced by invasion into surrounding soft tissue and bone, as well as by metastasis. This disease has been predominantly reported in the maxilla of large-breed dogs. Recognition of the aggressive nature of this type of lesion, despite deceptively benign histologic features, is imperative to avoid misdiagnosis and to facilitate early appropriate treatment.(1) Our patient was to have the mass re-biopsied, however after the CT study, per the owner’s request, the patient was humanely euthanized with no possibility of a necropsy or additional biopsies.

Reflex sympathetic dystrophy(2) is a poorly understood posttraumatic sequela of craniomandibular injury that results in pain, muscle wasting, skeletal demineralization, and disability more commonly reported in the human literature. It is theorized that reflex sympathetic dystrophy results from excessive sympathetic stimulation and/or parasympathetic nonfunction causing vasoconstriction and ischemia in the affected anatomic region, leading to pain and dystrophic changes such as muscle atrophy and skeletal demineralization. Considering the lesion in our dog did not extend to the level of the foramen ovale nor show obvious involvement of the trigeminal nerve, we were suspicious that a degree of reflex sympathetic dystrophy may have been involved in the degree of muscle atrophy that we observed.


  1. Ciekot PA, Powers BE, Withrow SJ, et al. Histologically low-grade, yet biologically high-grade, fibrosarcomas of the mandible and maxilla in dogs: 25 cases (1982-1991). JAVMA 1994; 204(4): 610-615.
  2. Schellhas KP. MR Imaging of Muscles of Mastication. AJR 1989; 154: 847-855