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Compendium July 2012 (Vol 34, No 7)

Clinical Snapshot: Unusual Skull Mass in a Mixed-Breed Dog

by Georgina Barone, DVM, DACVIM (Neurology)

    Case Presentation

    A 5-year-old, mixed-breed, intact female dog presented for evaluation of a mass on the head. The duration of clinical signs could not be ascertained from the owner, and little history was available. The physical examination revealed an extensive mass lesion encompassing the entire right side of the head, with severe craniofacial distortion. The right eye was unable to be visualized. The left orbit was deformed, with the mass partially obscuring the globe, and purulent ocular discharge was present. The right naris was completely obliterated and replaced with soft tissue. Stertorous respiration was evident, and the patient would occasionally breathe with its mouth open; referred upper airway sounds were ausculted, and there was an increased abdominal respiratory effort. Any manipulation of the face or mouth elicited significant pain. Gait, segmental reflexes, and postural responses were normal. A full cranial nerve examination was not possible due to severe facial distortion from the mass and apparent pain. Mentation was dull, and the dog appeared slightly disoriented. The patient was underweight with a body condition score of 3/9. Dysphagia and oral pain were evident when the patient attempted to eat or drink.

    A complete blood count (CBC) revealed a decreased hematocrit (33%; reference range: 36% to 60%). A reticulocyte count was not performed. A serum chemistry panel revealed moderate hypoalbuminemia (2.1 g/dL; reference range: 2.7 to 4.4 g/dL). The cause of the low albumin level was undetermined, and urinalysis was recommended but declined by the owner. The remainder of the chemistry panel results were within normal limits. Three-view thoracic radiographs were declined by the owner. Due to strong clinician interest and for teaching purposes, magnetic resonance imaging (MRI) of the skull was performed using a 1T Siemens Impact unit. Unfortunately, a full study with contrast could not be obtained due to anesthetic complications during the scan. Only T2 images (FIGURE A and FIGURE B) could be obtained.

    Sagittal MRI

    Figure A.

    Coronal MRI

    Figure B.

    1. What do these images show?

    2. What is the most likely diagnosis?

    3. What other imaging modalities might be used, and what features might they show?

    4. What is the biologic behavior of this disease, and what is the prognosis?

    Answers and Explanations

    1. T2 imaging is most useful for highlighting areas of increased water (edema), inflammation, or other pathologic processes. With this imaging sequence, fluid, edema, inflammation, and cerebrospinal fluid appear “hyperintense” (white), while with T1 imaging, fluid appears “hypointense” (dark) relative to surrounding tissue. Bony lesions or areas of calcification appear hypointense on both T1- and T2-weighted images.

    In FIGURE A (sagittal plane) and FIGURE B (coronal plane), a 16.1 × 13.7 × 13.3 cm, poorly demarcated mass lesion is evident. It encompasses the cranium with extensive involvement of the nasal cavity, frontal sinuses, oral cavity, and rostral prosencephalon.The prefrontal and frontal lobes are severely compressed (FIGURE A). Retrobulbar and periorbital involvement of the left eye is evident. The right eye is not visible in these images but was found to be deviated laterally and dorsally. The mass extends into the oral cavity with apparent obliteration of the palatine bone. Additionally, the nasal, maxillary, and frontal bones appear to have undergone complete osteolysis. Infiltration of the prefrontal and frontal lobes of the brain on the right side with perilesional edema and mild ventriculomegaly is seen. The mass has a multilobulated appearance and is primarily hyperintense (bright white in appearance) on T2-weighted images. However, there are foci of hypointensity within the mass, possibly representing hemorrhage or calcification.

    2. Diagnostic differentials for a skull mass include multilobular osteochondrosarcoma, osteosarcoma, and chondrosarcoma. In this case, histopathology of the mass was performed and findings were consistent with a low-grade, chondroblastic chondrosarcoma.

    3. Radiography and computed tomography (CT) may be of value. Features of chondrosarcoma that may be seen on plain radiography include bony lysis of affected tissues and, frequently, soft tissue calcification. MRI typically demonstrates lobulated lesions of high signal intensity (bright) on T2-weighted images and low signal intensity (dark) on T1-weighted images. Lobules may be separated by septa of low signal intensity. Areas of matrix calcification are shown as signal voids (black) on images obtained with all sequences, but small amounts of calcification may not be identifiable. MRI may be used to assess soft-tissue extension and the intramedullary extent of the tumor, but the histologic type or grade of the tumor generally cannot be characterized on routine MRI images. MRI is excellent for exact delineation of tumor extent and for assessing the tumor’s relationship to adjacent structures and intracranial involvement.1 However, while MRI is considered superior to CT for providing soft tissue detail, CT is often necessary if radiation therapy is to be instituted.

    4. Chondrosarcomas are malignant neoplasms representing 5% to 10% of all canine primary bone tumors.2 Chondrosarcomas arise from a variety of sites, including the ribs, pelvis, abdominal viscera, penis, omentum, aortic and heart valves, mammary glands, larynx, and trachea.3 Although chondrosarcoma of the skull is extremely rare in domestic species and humans (accounting for 0.1% of all head and neck neoplasms in people),4 it is most often identified in the nasal cavity and facial bones in dogs.2 In cases of nasal chondrosarcoma, the tumor initially invades the nasal cavity and surrounding recesses, leading to destruction of the ethmoid turbinates. Clinical signs of nasal chondrosarcoma include nasal discharge, epistaxis, obvious bony deformation, halitosis, exophthalmos, violent sneezing, seizures, or visual deficits. Because of the slow-growing nature of these tumors and the brain’s ability to adapt to compression over a protracted period of time, neurologic signs may not be observed until very late in the course of the disease. The metastatic potential of nasal chondrosarcoma is extremely low.

    The prognosis forcure is poor, but a favorable response to treatment is possible, with a reported median survival in dogs ranging from 210 to 580 days, depending on treatment modality (e.g., radiation, rhinotomy).3,5 Megavoltage radiation is the treatment of choice. There is no known reliable chemotherapeutic agent for treating this neoplasm.2 However, there is evidence that slow-release cisplatin may improve survival times when used in conjunction with radiotherapy.5

    ***

    In the dog featured in this report, it is presumed that the tumor arose from the nasal bones, but because the disease was so advanced and there was such widespread destruction of the affected tissues, it was difficult to determine the true origin. Due to the terminal stage of the disease, the dog was humanely euthanized.

    References

    1. Varma DGK, Ayala AG, Carrasco CH, et al. Chondrosarcoma: MR imaging with pathologic correlation. Radiographics 1992;12:687-704.

    2. Dernell WS. Tumors of the skeletal system. In: Withrow SJ, MacEwen EG, eds. Small Animal Clinical Oncology. 4th ed. Philadelphia, PA; Saunders; 2007:568-569.

    3. Popovitch CA, Weinstein MJ, Goldschmidt MH, et al. Chondrosarcoma: a retrospective study of 97 dogs (1987-1990). J Am Anim Hosp Assoc 1994;30:81-85.

    4. Koch BB, Karnell LH, Hoffman HT, et al. National cancer database report on chondrosarcoma of the head and neck. Head Neck 2000:22:408-425.

    5. Lana SE, Dernell WS, LaRue SM, et al. Slow release cisplatin combined with radiation for the treatment of canine nasal tumors. Vet Radiol Ultrasound 1997;38:474-478.

    References »

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