The location, size, geometry and neuropathological findings of
anaplastic astrocytomas (AA),
gliosarcomas and
sarcomas induced by the avian sarcoma virus (ASV) in dogs were compared with images generated using computerized tomography (CT) and real time high-resolution ultrasound (HRUS). Seven AA showed a wide range of findings on CT. Pre-contrast CT scans showed that the
tumors could be hyper, hypo, or isodense. Three of seven AA had no contrast enhancement; two of these
tumors were also isodense which resulted in a false-negative CT exam. Partial enhancement was seen in one
tumor. This resulted in a sensitivity of detection of 72%. Real time HRUS was able to define
tumor location, size and geometry of the AA missed or incompletely imaged by CT. All
tumors were hyperechoic. Inhomogeneity of the echo pattern was due to
hemorrhage,
cyst formation, and
necrosis within the
tumors. Such secondary
tumor characteristics were more accurately defined by HRUS compared to CT. Vasogenic
edema in the brain surrounding
tumors was of low density on CT and hypoechoic or indistinguishable from normal brain on US. Similar findings were seen in six
gliosarcomas, two of which were not visualized by either pre- or post-contrast enhanced CT scans (sensitivity of 66%).
Sarcomas differed in that they were either hyper or isodense; none were hypodense. The area of increased density matched the
tumor geometry and correlated with dense cellularity and
reticulin deposition. All 13
sarcomas showed contrast enhancement (100% sensitivity), but in two
tumors, contrast enhanced CT underestimated the size of the
tumor. Because of the large size and multiplicity of the
sarcomas, HRUS imaging was not able to resolve the entire
tumor volume because of limited imaging access. Intravenously injected
horseradish peroxidase (HRP) crossed the
tumor blood-brain barrier (BBB) only in those
tumors in which contrast enhancement was seen. These studies suggest that intraoperative HRUS imaging may be useful in detecting and delineating human AA incompletely visualized by CT.