Abstract
Granulomas can “mimic” gliomas on magnetic resonance imaging (MRI) in human patients. The goal of this retrospective study was to report canine brain granulomas that were consistent with glioma based upon MRI, report their histologic diagnosis, and identify MRI criteria that might be useful to distinguish granuloma from glioma. Ten granulomas, initially suspected to be glioma based on MRI, were ultimately diagnosed as granulomatous meningoencephalomyelitis (n = 5), infectious granulomas (n = 3) or other meningoencephalitis (n = 2). Age was 1.6–15.0 years and two dogs were brachycephalic breeds. MRI characteristics overlapping with glioma included intra-axial, heterogeneous, T2-weighted hyperintense, T1-weighted hypointense to isointense mass lesions with contrast-enhancement. Signals on fluid attenuation inversion recovery, gradient echo and diffusion weighted imaging also matched glioma. Peri-lesional edema and mass effect were toward the high end of findings reported for glioma. MRI characteristics that would be considered unusual for glioma included dural contact (n = 4), T2-hypointensity (n = 2), concomitant meningeal-enhancement (n = 9), and minor changes in the contralateral brain (n = 2). Cerebrospinal fluid analysis revealed albuminocytological dissociation or mild pleocytosis. These cases show that granulomas can “mimic” glioma on canine brain MRI. In individual cases, certain MRI findings may help increase the index of suspicion for granuloma. Lack of pronounced cerebrospinal fluid pleocytosis does not exclude granuloma. Signalment is very useful in the suspicion of glioma, and many of these dogs with granuloma were of ages and breeds in which glioma is less commonly seen.
Highlights
In human medicine, many intracranial inflammatory processes may have magnetic resonance imaging (MRI) characteristics that suggest glioma
In dogs fungal granuloma can be mistaken for glioma on MRI [13, 14] and both should be included in the differential diagnosis for intra-axial masses with peripheral contrast-enhancement [15, 16]
Margins of the lesions varied greatly from well-defined and regular to poorly defined and irregular. These cases show that granuloma can “mimic” glioma on brain MRI of dogs and granuloma should not be prematurely excluded from the differential diagnosis
Summary
Many intracranial inflammatory processes may have magnetic resonance imaging (MRI) characteristics that suggest glioma. Other inflammatory syndromes with MRI characteristics suggestive of glioma include fungal granuloma [8], eosinophilic granuloma [9], foreign body reactions to surgical [10], or embolization material [11], or inflammatory. Granulomas Mimicking Glioma on MRI pseudotumor [12]. Other granulomas with a neoplasm-like MRI appearance include cholesterol granuloma [17], granulomatous Acanthamoeba encephalitis [18], inflammatory pseudotumor [19], and the focal form of granulomatous meningoencephalomyelitis (GME) [20]. The cerebral white matter is a prime location for multiple perivascular cuffs to coalesce into a singular granuloma [22], adding to the MRI difficulty in distinguishing between GME and glioma
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