Ebook Veterinary diagnostic imaging, the dog and cat (Vol 1): Part 2

Part 2 book "Veterinary diagnostic imaging, the dog and cat" includes content: Skull tumors, nasal cavity disease, dental, gum, and tongue diseases, brain disease and injury, the ear, the eye and orbit, miscellaneous diseases, the spine, congenital spinal malformations (congenital spinal anomalies)....and other contents.
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Ebook Veterinary diagnostic imaging, the dog and cat (Vol 1): Part 2 C h a p t e r 1 3 Skull Tumors Skull tumors vary in radiographic appearance accord- tinctive dished-out areas, reflecting areas of creeping ing to both their cell type and location. For example, substitution (Box 13-2). osteosarcomas of the cranial vault are typically pro- ductive with defined margins, whereas osteosarcomas in long bones are usually destructive and poorly mar- ❚❚❚ MANDIBULAR TUMORS ginated. Osteosarcomas of the face and jaw, on the other hand, typically feature creeping osteolysis, overt cor- Background tical destruction, and tumor bone extending into the surrounding soft tissue.1 Most mandibular tumors are actually squamous cell carcinomas (or other soft tissue tumors) of the gum or tongue, which become evident radiographically only ❚❚❚ CRANIAL TUMORS once they invade the nearby jawbone. Primary bone tumors such as osteosarcoma, fibrosarcoma, and chon- Radiology and Computed Tomography drosarcoma also may develop in the lower jaw but do so considerably less often (Figure 13-10). Because of the pronounced curvature of the cranium, Thrall and co-workers reported the development tangential views, made at right angles to suspicious of a mandibular osteosarcoma in a dog 77 months surfaces, often produce a diagnostic image (Figure after orthovoltage radiotherapy for a fibromatous 13-1) where standard lateral and ventrodorsal pro- epulis (periodontal origin, acanthomatous type).3 jections of the same region fail to reveal any abnor- To qualify as a radiation-induced bone tumor, a lesion malities (Figure 13-2). Some cranial osteosarcomas must meet the following criteria (according to the produce relatively little soft tissue swelling while authors): extensively lysing underlying bone (Figures 13-3 and 13-4). • Microscopic or radiographic evidence must exist that Hathcock and Newton described the computed the original bone, whether normal or not, was non- tomographic (CT) appearance of seven cranial and malignant. two facial bone tumors in dogs. These bones were • The tumor must have developed within previously optimally imaged using a bone window.2 The prin- irradiated tissue. cipal CT features of these tumors are shown in • The latent period between irradiation and tumor Box 13-1. detection must be long. • The malignant nature of the tumor suspected to be radiation-induced must be proved. ❚❚❚ FACIAL TUMORS Radiology and Computed Tomography Imaging Findings Radiographically, facial malignancies can be quite vari- Most invasive gingival and glossal cancers cause local able in appearance, ranging from intensely destruc- bony destruction; however, some do not. On the tive (Figure 13-5) to moderately productive; contrary, there are reports of invasive carcinomas alternatively, they may feature a combination of pro- causing intensely productive mandibular lesions ductive and destructive changes (Figures 13-6 to 13- resembling primary bone tumors.4 Mixed (destruc- 8). Most, however, are primarily destructive (Figure tive–productive) mandibular tumors occur as well 13-9). Tomographically, facial tumors often feature dis- (Figures 13-11 to 13-15). 199 Figure 13-1 • Osteosarcoma: A slightly oblique lateral view of the cranium of a dog shows a faint, smoothly surfaced mound of tumor bone, underlain by a ragged area of cortical destruction (emphasis zone). Figure 13-2 • An earlier true lateral view of the same region Figure 13-4 • Close-up view of the cranium of a dog shows a predictably failed to show this eccentrically located bone tumor. vaguely marginated area of uneven bone destruction (sometimes referred to as permeative), which in this instance is being caused by an osteosarcoma. Figure 13-3 • Orientation view of the cranium of a dog shows a Figure 13-5 • Ventrodorsal open-mouth view of the skull of a cat vaguely marginated area of uneven bone destruction (sometimes with a highly destructive carcinoma that has destroyed much of referred to as permeative), which in this instance is being caused the right side of the face (emphasis zone). by an osteosarcoma. CHAPTER 13 ❚❚❚ Skull Tumors 201 Figure 13-6 • Lateral view of a cat with a squamous cell carcinoma of the rostral aspect of the right zygoma. Note how lesion visibility varies depending on projection, attesting to the Figure 13-7 • Ventrodorsal view of a ...