ABSTRACT A 7 yr old female spayed Chihuahua-terrier mix was presented for a progressive dry, hacking cough over 9 mo, with dyspnea aggravated by eating and drinking. Computed tomography of the skull revealed a large mineral attenuating mass associated with the left skull base, without intracranial involvement. A modified ventral paramedian hypophysectomy approach along the medial aspect of the left ramus was used to approach the base of the skull. Ninety percent of the mass was debulked via high-speed pneumatic burr. Histopathology was consistent with hyperostosis originating from a primary extracranial meningioma (ECM), with the tissue staining positive for vimentin and negative for cytokeratin. The patient was symptom free for 9 mo before clinical signs returned because of tumor recurrence and was euthanized 11 mo postoperation because of diminished quality of life. ECM is uncommonly reported in the dog, and to the authors’ knowledge has not previously been reported with hyperostosis or located along the skull base at the level of the tympanic bulla. Additionally, although hyperostosis predominantly occurs as diffuse bone thickening adjacent to a meningioma, proliferative focal hyperostosis is uncommon. Given the findings in this patient, ECM should be considered as a differential diagnosis for osseous skull base masses.

ABSTRACT This retrospective case series describes seven dogs and one cat diagnosed with dedifferentiated chondrosarcoma, an uncommon, aggressive variant of chondrosarcoma. The purpose of the study is to describe clinical, imaging, and histopathological findings of this tumor. Medical records and the diagnostic laboratory database at Colorado State University from 2000 to 2015 were reviewed and complete medical records were available for the eight animals in this report. Similar to what has been reported in people, poor long-term survival and high metastatic rate, particularly to the lungs, was observed in our case series. A bimorphic pattern on imaging (radiographs, computed tomography, and MRI) consisting of mineralized and nonmineralized areas was seen mirroring the high-grade sarcomatous component adjacent to a low-grade chondroid component seen histopathologically. A review of the human literature including suspected etiology, imaging findings, histopathology, and survival times with various treatment options is presented. This article describes the first reported cases of dedifferentiated chondrosarcoma in the veterinary literature. Early accurate recognition could lead to treatment plans tailored to this variant.