Glioma Mimics: Magnetic Resonance Imaging Characteristics of Granulomas in Dogs

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.

Definitive-intent uniform megavoltage fractioned radiotherapy protocol for presumed canine intracranial gliomas: retrospective analysis of survival and prognostic factors in 38 cases (2013–2019)

“…The clinical-imaging exclusion criteria were inspired by Dolera [ 10 ], and implemented as followed: Previous chemotherapy or surgical treatment of the tumour; Lesion localization close to a vascular territory of a main cerebral artery or a perforating artery with sharp demarcation [ 42 ], strong hyperintensity in the diffusion image and hypointensity on ADC (Apparent Diffusion Coefficient) map [ 40 ] suggesting a vascular origin [ 40 , 42 , 46 ]; Fever/other symptoms or blood abnormalities correlated with inflammation, presence of any predisposing factor to infection, image characteristics of an abscess (T2-Weighted images (T2-WI) hypointense peripheral rim or peripheral concentric “onion skin like” hypointense rim, thick strong peripheral rim contrast enhancement [ 47 ] or a granuloma (dural contact, T2-WI hypointensity) [ 48 ] and concurrent findings of meningitis [ 48 , 49 ]; these aspects were considered indicative of inflammatory diseases [ 38 ]; Well defined rounded structure, isolated or in continuity with ventricles and cisterns with thin, smooth non-enhancing walls and content resembling cerebrospinal fluid (CSF) or fat, that did not display contrast enhancement, were considered congenital intracranial cysts (arachnoid or dermoid cysts) [ 50 ]. …”

“…Fever/other symptoms or blood abnormalities correlated with inflammation, presence of any predisposing factor to infection, image characteristics of an abscess (T2-Weighted images (T2-WI) hypointense peripheral rim or peripheral concentric “onion skin like” hypointense rim, thick strong peripheral rim contrast enhancement [ 47 ] or a granuloma (dural contact, T2-WI hypointensity) [ 48 ] and concurrent findings of meningitis [ 48 , 49 ]; these aspects were considered indicative of inflammatory diseases [ 38 ];…”

Definitive-intent uniform megavoltage fractioned radiotherapy protocol for presumed canine intracranial gliomas: retrospective analysis of survival and prognostic factors in 38 cases (2013-2019).

“…hypointense peripheral rim or peripheral concentric "onion skin like" hypointense rim, thick strong peripheral rim contrast enhancement [27] or a granuloma (dural contact, T2-WI hypointensity) [28]and concurrent ndings of meningitis [28,29]; these aspects were considered indicative of in ammatory diseases [30];…”

Definitive-intent uniform megavoltage fractioned radiotherapy protocol for presumed canine intracranial gliomas: retrospective analysis of survival and prognostic factors in 38 cases (2013-2019).

“…-Fever/other symptoms or blood abnormalities correlated with inflammation, presence of any predisposing factor to infection, image characteristics of an abscess (T2-Weighted images (T2-WI) hypointense peripheral rim or peripheral concentric "onion skin like" hypointense rim, thick strong peripheral rim contrast enhancement [27] or a granuloma (dural contact, T2-WI hypointensity) [28] and concurrent findings of meningitis [28,29]; these aspects were considered indicative of inflammatory diseases [30]; -Well defined rounded structure, isolated or in continuity with ventricles and cisterns with thin, smooth non-enhancing walls and content resembling cerebrospinal fluid (CSF) or fat, that did not display contrast enhancement, were considered congenital intracranial cysts (arachnoid or dermoid cysts) [31].…”