Magnetic resonance imaging (MRI) and computed tomographic imaging (CT) characteristics of intracranial intra-arachnoid cysts in six dogs are described. Of the six dogs, three were less than one year of age and 4 were males. Five of the six dogs weighed less than 11 kg. Five cysts were located in the quadrigeminal cistern. On CT images, the intracranial intra-arachnoid cysts had sharply defined margins, contained fluid isodense to CSF and did not enhance following i.v. administration of contrast. On MRI images, the intracranial intra-arachnoid cysts were extra-axial, contained fluid isointense with CSF and did not enhance following i.v. contrast. While spinal arachnoid cysts of dogs have been reported in the literature, other than the six dogs contained in this report, intracranial intra-arachnoid cysts have not to our knowledge been described in animals. These six dogs have a similar age, sex, history, clinical signs, CT and MRI findings to those reported in people with intracranial intra-arachnoid cysts.
Magnetic resonance imaging (MRI) examinations from 18 dogs with a histologically confirmed peripheral nerve sheath tumor (PNST) of the brachial plexus were assessed retrospectively. Almost half (8/18) had a diffuse thickening of the brachial plexus nerve(s), six of which extended into the vertebral canal. The other 10/18 dogs had a nodule or mass in the axilla (1.2-338 cm3). Seven of those 10 masses also had diffuse nerve sheath thickening, three of which extended into the vertebral canal. The majority of tumors were hyperintense to muscle on T2-weighted images and isointense on T1-weighted images. Eight of 18 PNSTs had only minimal to mild contrast enhancement and many (13/18) enhanced heterogeneously following gadolinium DTPA administration. Transverse plane images with a large enough field of view (FOV) to include both axillae and the vertebral canal were essential, allowing in-slice comparison to detect lesions by asymmetry of structures. Higher resolution, smaller FOV, multiplanar examination of the cervicothoracic spine was important for appreciating nerve root and foraminal involvement. Short tau inversion recovery, T2-weighted, pre and postcontrast T1-weighted pulse sequences were all useful. Contrast enhancement was critical to detecting subtle diffuse nerve sheath involvement or small isointense nodules, and for accurately identifying the full extent of disease. Some canine brachial plexus tumors can be challenging to detect, requiring a rigorous multiplanar multi-pulse sequence MRI examination.
This retrospective analysis of 15 dogs with postcontrast ring enhancing brain lesions, each detected by a single Computed Tomography [CT] examination, searched for any association between their CT appearance and the pathologic diagnosis. In a subgroup of these dogs [n = 7] necropsied within 2 days of the last CT scan, we evaluated whether there was any anatomic correlation between the ring zone and the histopathologic features of the lesions. Our study consisted of eight dogs with primary brain tumors [3 meningiomas, 3 astrocytomas, 1 mixed glioma, 1 oligodendroglioma], 4 with metastatic brain tumors [2 fibrosarcomas, 1 mammary carcinoma, 1 melanoma] and 3 with non‐neoplastic brain lesions [2 intraparenchymal hemorrhages, 1 pyogranulomatous meningoencephalitis]. The overall size and shape of the contrast enhancing CT lesions, as well as the thickness, surface texture and degree of enhancement of the ring were subjectively evaluated. No association was found between the CT lesion characteristics and the pathologic diagnosis. In the sub‐group of dogs euthanatized within 2 days of the CT examination, distinct histologic features which anatomically correlated with the zone of ring enhancement were found in 3 of 7 lesions. The findings of this study are consistent with those of ring‐enhancing lesions in people, and indicates that CT ring enhancement is a non‐specific phenomenon which can occur in a variety of neoplastic and non‐neoplastic lesions in the dog.
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