A considerable amount of information in the literature describes the occurrence of tumors in the central nervous system (CNS)
in different animal species. Intracranial neoplasia is recognized less frequently in cats than in dogs. CNS tumors can be
either a primary neoplasm, a secondary neoplasm from an extra-cranial primary site metastasizing to the CNS, or a non-neoplastic
mass effect that can mimic neoplasia. Diagnosis of an intracranial tumor is a major challenge. Cerebrospinal fluid (CSF) analysis
and skull radiographs rarely are specific for diagnosing CNS tumors. Lesions can be detected by using computed tomography
(CT) or magnetic resonance imaging (MRI). Magnetic resonance imaging equipment now is widely available and is being marketed
directly to veterinarians by manufacturers. However, little information is available regarding MRI features of intracranial
tumors in cats. In a retrospective study
(Magnetic Resonance Imaging Features of Feline Intracranial Neoplasia: Retrospective Analysis of 46 Cats. J Vet Intern Med
, Troxel and coworkers reviewed the MRI features of histologically confirmed brain tumors in cats and determined whether or
not these characteristics could be used to predict tumor type accurately. Table 1 shows the distribution of tumor cell types
observed in this group.
The authors identified several patterns of MRI characteristics among tumor types that assisted with the prediction of histologic
tumor type. Most extra-axial masses (those located outside of the brain parenchyma) that had moderate-to-marked contrast enhancement
and a dural tail were found to be meningiomas. Extra-axial masses that caused mild edema and showed evidence of chronic hemorrhage
or mineralization always were meningiomas. Most extra-axial masses with a hyperintense signal on T2-weighted images, isointense
or hypointense signal on T1-weighted images, and moderate-to-marked contrast enhancement were meningiomas, whereas lymphomas
and pituitary tumors accounted for only 10 percent of cases with these imaging characteristics. All intra-axial (within the
brain parenchyma) masses with ring enhancement and cystic regions were gliomas.
Among meningiomas, peritumoral edema varied considerably but was mild most of the time. Although rare, cyst formation was
seen. Transtentorial and cerebellar herniation occurred respectively in approximately 42 percent and 21 percent of cats with
Lymphomas were either intra-axial or extra-axial. Signal intensity generally was hyperintense and heterogenous on T2 images
and isointense or hypointense on T1 images and was homogenous in all cats. Proton density weighted images were hyperintense
and heterogenous. Peritumoral edema was seen in all cats. Mass effect was seen in half of the cat population with lymphomas
in which an extra-axial mass was identified, and a dural tail sign was identified in one of the six cats in this group.
MRI images were obtained in one cat with an astrocytoma and three cats with oligodendrogliomas. These intra-axial tumors were
round, hyperintense on T2, and hypointense on T1 images. All four tumors had ring enhancement. Mild to moderate peritumoral
edema was noted in most cats. Some of the gliomas appeared to be cystic.
Two cases of olfactory neuroblastoma were described by the authors. Both tumors were extra-axial, ovoid with irregular and
indistinct borders, and appeared to break through the cribriform plate, causing a mass effect. T2 images were either hyperintense
or isointense, and both had a heterogenous pattern. T1 images were either hyperintense or hypointense. A homogenous pattern
was seen on T1 images. Isointense images were recorded on proton density images. There was a heterogenous enhancement in both
tumors and moderate to marked peritumoral edema. Chronic hemorrhage or mineralization was suspected.
In one case, a pituitary tumor appeared round with regular and distinct margins. Images were hypointense and heterogenous
on T2 images, and isointense and heterogenous on T1 images. There was moderate, heterogenous, ring-enhancing contrast enhancement.