Glioma Mimics: Magnetic Resonance Imaging Characteristics of Granulomas in Dogs

Clinicopathological and diagnostic imaging findings in a dog with neurocandidiasis

Neurocandidiasis is systemic candidiasis with central nervous system involvement. This case report describes the clinical presentation, diagnostic test results, and histopathology of a dog with neurocandidiasis. A 3-year-old German shepherd dog was presented for a 3-day history of abnormal mentation, neck pain, and ataxia. Magnetic resonance imaging (MRI) scan of the brain revealed multifocal, small, round, intra-axial lesions within the forebrain. Examination of the cerebrospinal fluid revealed severe neutrophilic inflammation. Extensive testing for infectious diseases was negative. The dog was administered immunosuppressive doses of corticosteroids. The dog's clinical signs improved transiently but got worse 12 days after starting the treatment. Repeat MRI scan revealed multiple, intra-axial, target-like nodular lesions scattered throughout the brain parenchyma. In the temporal muscles, nodules were seen. Cytology of the fine needle aspirates of the nodules in the temporal muscles revealed a neutrophilic inflammation with hyalohyphomycosis. Postmortem examination was compatible with a severe systemic fungal infection. Candida albicans was isolated from the brain, kidney, and heart.

Chemotherapy for the treatment of intracranial glioma in dogs

Gliomas are the second most common primary brain tumor in dogs and although they are associated with a poor prognosis, limited data are available relating to the efficacy of standard therapeutic options such as surgery, radiation and chemotherapy. Additionally, canine glioma is gaining relevance as a naturally occurring animal model that recapitulates human disease with fidelity. There is an intense comparative research drive to test new therapeutic approaches in dogs and assess if results translate efficiently into human clinical trials to improve the poor outcomes associated with the current standard-of-care. However, the paucity of data and controversy around most appropriate treatment for intracranial gliomas in dogs make comparisons among modalities troublesome. To further inform therapeutic decision-making, client discussion, and future studies evaluating treatment responses, the outcomes of 127 dogs with intracranial glioma, either presumed (n = 49) or histologically confirmed (n = 78), that received chemotherapy as leading or adjuvant treatment are reviewed here. This review highlights the status of current chemotherapeutic approaches to intracranial gliomas in dogs, most notably temozolomide and lomustine; areas of novel treatment currently in development, and difficulties to consensuate and compare different study observations. Finally, suggestions are made to facilitate evidence-based research in the field of canine glioma therapeutics.

A comparison between neurological clinical signs, cerebrospinal fluid analysis, cross-sectional CNS imaging, and infectious disease testing in 168 dogs with infectious or immune-mediated meningoencephalomyelitis from Brazil

This retrospective study evaluated canine patients with presumptively diagnosed meningoencephalomyelitis (ME) based on neurological clinical signs, cerebrospinal fluid (CSF) analysis, cross-sectional imaging, and infectious disease testing with a limited neurological-focused polymerase chain reaction (PCR) panel performed on blood and CSF. The first goal was to determine the proportion of dogs where the condition was caused by an infectious agent versus a probable immune-mediated etiology (i.e., meningoencephalomyelitis of unknown origin; MUO) in our geographic region. The secondary goals of this study were to examine and define associations between abnormal CSF test results and cross-sectional neuroimaging findings, in addition to defining the age and most common neurological clinical signs in each group of ME. A total of 168 dogs matched the inclusion criteria with magnetic resonance imaging (MRI) performed in 130 dogs and computed tomography (CT) performed in 38 dogs. Presumptive MUO was observed in 152/168 (90.5%) of dogs and infectious ME was identified in 16/168 (9.5%) of dogs (p < 0.0001). Canine distemper virus (CDV) was the most common cause of infectious ME in 10/16 dogs (62.5%). Of the total cases with a positive infectious disease result, 3/16 (18.7%) had normal CSF results and 13/16 (81.3%) had abnormal CSF results (p = 0.0078). MRI and CT abnormalities in the brain were detected in 74 and 39% of dogs with inflammatory CSF, respectively. MRI and CT abnormalities in the spinal cord were detected in 90 and 57% of dogs with inflammatory CSF results, respectively. Age was not significantly different between infectious ME and presumptive MUO groups (p = 0.15). Seizures were the most common clinical sign reported for both MUO (36.8% of cases) and infectious ME (31.2% of cases). In conclusion, presumptive MUO is significantly more common than infectious ME in this population of dogs. Furthermore, although normal CSF results were uncommon in dogs with infectious ME, this finding occurred in several patients (3/16), suggesting that infectious disease testing should be considered even in the face of normal CSF results. Finally, MRI was more sensitive than CT in the detection of abnormalities when dogs with ME had inflammatory CSF results but was not 100% sensitive, suggesting CSF analysis should be performed to rule out inflammation even when no abnormalities are detected on MRI or CT.

The T2-FLAIR mismatch sign as an imaging biomarker for oligodendrogliomas in dogs

BACKGROUND

In humans, the T2-weighted (T2W)-fluid-attenuated inversion recovery (FLAIR) mismatch sign (T2FMM) is a specific imaging biomarker for the isocitrate dehydrogenase 1 (IDH1)-mutated, 1p/19q non-codeleted low-grade astrocytomas (LGA). The T2FMM is characterized by a homogeneous hyperintense T2W signal and a hypointense signal with a hyperintense peripheral rim on FLAIR sequences. In gliomas in dogs, the T2FMM has not been described.

HYPOTHESES/OBJECTIVES

In dogs with focal intra-axial brain lesions, T2FMM will discriminate gliomas from other lesions. The T2FMM will be associated with the LGA phenotype and presence of microcysts on histopathology. Interobserver agreement for T2FMM magnetic resonance imaging (MRI) features will be high.

ANIMALS

One hundred eighty-six dogs with histopathologically diagnosed focal intra-axial lesions on brain MRI including oligodendrogliomas (n = 90), astrocytomas (n = 47), undefined gliomas (n = 9), cerebrovascular accidents (n = 33), and inflammatory lesions (n = 7).

METHODS

Two blinded raters evaluated the 186 MRI studies and identified cases with the T2FMM. Histopathologic and immunohistochemical slides of T2FMM cases were evaluated for morphologic features and IDH1-mutations and compared to cases without the T2FMM. Gene expression analyses were performed on a subset of oligodendrogliomas (n = 10) with and without T2FMM.

RESULTS

The T2FMM was identified in 14/186 (8%) of MRI studies, and all dogs with T2FMM had oligodendrogliomas (n = 12 low-grade [LGO], n = 2 high-grade [HGO]; P < .001). Microcystic change was significantly associated with the T2FMM (P < .00001). In oligodendrogliomas with T2FMM, IDH1-mutations or specific differentially expressed genes were not identified.

CONCLUSION AND CLINICAL IMPORTANCE

The T2FMM can be readily identified on routinely obtained MRI sequences. It is a specific biomarker for oligodendroglioma in dogs, and was significantly associated with non-enhancing LGO.

Rapid brain MRI protocols result in comparable differential diagnoses versus a full brain protocol in most canine and feline cases

Evaluation of brain disease in veterinary patients uses a wide variety of MRI sequences. A shortened protocol that maintains consistency of interpretation would reduce radiologist reporting time, patient anesthetic time, and client cost. The aims of this retrospective, methods comparison, observer agreement study were to evaluate whether abbreviated MRI protocols alter differential diagnoses and recommendations compared to our institution's standard protocol; evaluate interobserver agreement on standard brain MRIs; and assess whether differential diagnoses change after postcontrast images. Normal and pathologic canine and feline brain MRIs were retrieved from hospital archives. Three protocols were created from each: a 5-sequence noncontrast enhanced Fast Brain Protocol 1 (FBP1); a 6-sequence contrast-enhanced Fast Brain Protocol 2 (FBP2); and an 11-sequence standard brain protocol (SBP). Three blinded veterinary radiologists interpreted FBP images for 98 cases (1 reader/case) and SBP images for 20 cases (3 readers/case). A fourth observer compared these interpretations to the original MRI reports (OMR). Overall agreement between FBPs and OMR was good (k = 0.75) and comparable to interobserver agreement for multiple reviews of SBP cases. Postcontrast images substantially altered conclusions in 17/97 cases (17.5%), as well as improved interobserver agreement compared to noncontrast studies. The conclusions reached with shortened brain protocols were comparable to those of a full brain study. The findings supported the use of a 6-sequence brain MRI protocol (sagittal T2-weighted [T2w] TSE; transverse T2w turbo spin echo fluid-attenuated inversion recovery, T2*-weighted gradient recalled echo, T1-weighted spin echo, and diffusion weighted imaging/apparent diffusion coefficient; and postcontrast transverse T1-weighted spin echo) for dogs and cats with suspected intracranial disease.

Case report: MRI findings with CNS blastomycosis in three domestic cats

Blastomycosis is a systemic mycotic infection caused by dimorphic fungi. The disease is rare in cats, and reports on imaging findings with central nervous system (CNS) involvement are limited. Magnetic resonance imaging (MRI) was performed antemortem in three feline patients. Imaging findings that may allow prioritization of intracranial blastomycosis over other differential diagnoses included focal or multifocal intra-axial mass lesions with dural contact, lesion hypointensity on T2-weighted images and diffusion-weighted imaging/apparent diffusion coefficient map (DWI/ADC), strong and homogeneous contrast enhancement of the lesion(s), concurrent meningeal enhancement, marked perilesional edema and mass-effect, and ocular abnormalities. One cat was managed successfully and had a recurrence of CNS blastomycosis more than 4.5 years after the initial diagnosis. Repeat MRI at that point revealed both new and persistent (chronic) abnormalities.

Feasability of a Frameless Brain Biopsy System for Companion Animals Using Cone-Beam CT-Based Automated Registration

The aim of the present study was to evaluate the use of a novel intraoperative cone-beam computed tomography (CBCT)-based automated registration system for frameless stereotactic brain biopsy in companion animals. An experimental cadaveric study evaluated thalamic and piriform lobe target site needle placement error in three dogs and three cats without a history of intracranial disease. Diagnostic accuracy and diagnostic yield were prospectively evaluated in twenty-four client-owned dogs and four cats with intracranial disease. Twenty-one procedures were performed post mortem (eighteen dogs and three cats), and seven biopsy procedures were performed in alive patients (six dogs and one cat). Procedural duration was evaluated in ten post mortem and four living patients. Outcome was evaluated in six dogs and one cat. In dogs, the calculated median needle placement error was 1.8 mm (range 0.71–2.84 mm) and 1.53 mm (range 1.45–1.99 mm) for piriform lobe and thalamus target sites, respectively. In cats, the calculated median needle placement error was 0.79 mm (range 0.6–1.91 mm) for the piriform lobe target site and 1.29 mm (range 0.47–2.69 mm) for the thalamic target site. The diagnostic yield was 96.4% (95% CI 0.81–0.99), the diagnostic accuracy was 94.4% (95% CI 0.72–0.99). Median total procedural duration for post mortem biopsies was 57.5 min (range 41–69 min). Median total procedural duration for intra vitam biopsies was 122.5 min (range 103–136 min). Three dogs were discharged 1 day after biopsy and one dog after 6 days. Two dogs and one cat were euthanized 24 and 48 h after biopsy. Intraoperative CBCT-based automated image registration for frameless stereotactic biopsies in companion animals is capable of providing diagnostic brain biopsy specimens independent of skull size and morphology with diagnostic yield and accuracy comparable to published values for diverse frameless and frame-based stereotaxy systems used in veterinary medicine. Duration of the procedure is not negatively affected and within the published range with other systems. Mobile intraoperative CBCT-based registration combined with neuronavigation delivers diagnostic brain biopsies in companion animals.

Retrospective evaluation of hyperproteinorrachia without pleocytosis (albuminocytologic dissociation) and survival in dogs

BACKGROUND

Hyperproteinorrachia (raised cerebrospinal fluid total protein [CSF-TP]) without pleocytosis (HP) (also known as albuminocytologic dissociation) is identified in dogs with different neurologic diseases. However, the association between survival and increased CSF-TP is unknown.

OBJECTIVES

(a) Identify conditions commonly associated with HP in dogs and (b) investigate whether higher CSF-TP concentrations or other relevant factors are associated with 1-year survival.

METHODS

This is a retrospective study that identified dogs with HP (Cisternal CSF-TP >0.30 g/L, Lumbar CSF-TP >0.45 g/L with total nucleated cell concentrations [TNCCs] and RBC counts within RIs) from 2008 to 2019: recording signalment, weight, vital parameters, inflammation, neuroanatomic localization, CSF-TP, sampling site, final diagnosis, etiologic classification, and 1-year survival. Corrected CSF-TP was calculated as CSF-TP minus 0.3 (cisternal) or 0.45 (lumbar or unknown). Descriptive statistics were produced, CSF-TP differences between groups (eg, neuroanatomic localizations) were evaluated using the Mann-Whitney U test or Kruskal-Wallis test (post-hoc testing). The Cox proportional hazards model was used for survival data. Statistical significance was set at a P < 0.05.

RESULTS

In all, 39 dogs had HP, associated with 17 conditions, including neoplasia (n = 6), meningoencephalitis of unknown origin (n = 4) (MUO), and intervertebral disc disease (n = 4) (IVDD) as the most common conditions. There was no significant difference between the CSF-TP/corrected CSF-TP between 1-year survivors and non-survivors, nor was there a difference between different neuroanatomic localizations or etiologic classifications (P > 0.05). Neoplasia, after adjustment for age, was the only variable associated with a worse survival (P = 0.01 HR: 2.08 (95% CI: 1.65-39.2). CSF-TP was not associated with age (P > 0.05).

CONCLUSIONS

HP in dogs is associated with a wide range of conditions; the most common conditions are neoplasia, MUO, and IVDD. Higher CSF-TP levels do not correlate with a worse 1-year survival; however, they do correlate with neoplastic lesions.

Classification of neoplastic and inflammatory brain disease using MRI texture analysis in 119 dogs

Magnetic resonance imaging is the primary method used to diagnose canine glial cell neoplasia and noninfectious inflammatory meningoencephalitis. Subjective differentiation of these diseases can be difficult due to overlapping imaging characteristics. This study utilizes texture analysis (TA) of intra-axial lesions both as a means to quantitatively differentiate these broad categories of disease and to help identify glial tumor grade/cell type and specific meningoencephalitis subtype in a group of 119 dogs with histologically confirmed diagnoses. Fifty-nine dogs with gliomas and 60 dogs with noninfectious inflammatory meningoencephalitis were retrospectively recruited and randomly split into training (n = 80) and test (n = 39) cohorts. Forty-five of 120 texture metrics differed significantly between cohorts after correcting for multiple testing (false discovery rate < 0.05). After training the random forest algorithm, the classification accuracy for the test set was 85% (sensitivity 89%, specificity 81%). TA was only partially able to differentiate the inflammatory subtypes (granulomatous meningoencephalitis [GME], necrotizing meningoencephalitis [NME], and necrotizing leukoencephalitis [NLE]) (out-of-bag error rate of 35.0%) and was unable to identify metrics that could correctly classify glioma grade or cell type (out-of-bag error rate of 59.6% and 47.5%, respectively). Multiple demographic differences, such as patient age, sex, weight, and breed were identified between disease cohorts and subtypes which may be useful in prioritizing differential diagnoses. TA of MR images with a random forest algorithm provided classification accuracy of inflammatory and neoplastic brain disease approaching the accuracy of previously reported subjective radiologist evaluation.

Vascular endothelial growth factor concentrations in the cerebrospinal fluid of dogs with neoplastic or inflammatory central nervous system disorders

Background

Vascular endothelial growth factor (VEGF) is a key molecular driver of angiogenesis and vascular permeability and is expressed by a wide variety of neoplasms. Although blood VEGF concentrations have been quantified in intracranial tumors of dogs, cerebrospinal fluid (CSF) VEGF concentration might be a more sensitive biomarker of disease.

Objective

Concentrations of VEGF in CSF are higher in dogs with central nervous system (CNS) neoplasia compared to those with meningoencephalomyelitis and other neurologic disorders.

Animals

One hundred and twenty‐six client‐owned dogs presented to a veterinary teaching hospital.

Methods

Case‐control study. Cerebrospinal fluid was archived from dogs diagnosed with CNS neoplasia and meningoencephalomyelitis. Control dogs had other neurological disorders or diseases outside of the CNS. A commercially available kit was used to determine VEGF concentrations.

Results

Detectable CSF VEGF concentrations were present in 49/63 (77.8%) neoplastic samples, 22/24 (91.7%) inflammatory samples, and 8/39 (20.5%) control samples. The VEGF concentrations were significantly different between groups (P < .0001), and multiple comparison testing showed that both neoplastic and inflammatory groups had significantly higher concentrations than did controls (P < .05), but did not differ from each other. Gliomas and choroid plexus tumors had significantly higher VEGF concentrations than did the control group (P < .05).

Conclusions and Clinical Importance

Cerebrospinal fluid VEGF concentrations may serve as a marker of neoplastic and inflammatory CNS disorders relative to other conditions.

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

Background

Radiotherapy (RT) is currently considered the treatment of choice for presumed canine intracranial gliomas. However, variable therapeutic responses are described, due to heterogeneous populations and different radiation methods or protocols. Only one study dedicated to intracranial suspected glioma highlighted prognostic criteria. Determination or confirmation of specific clinical and imaging prognostic factors may guide the therapeutic management of these tumours. The objectives were to provide data on long-term clinical outcome (including quality of life, QoL) and to determine specific prognostic factors associated with survival time. We report a single-institution retrospective study, including all dogs with suspected symptomatic primary solitary intracranial glioma, treated with a complete uniform fractionated megavoltage radiation protocol of 15x3Gy over 5 weeks, between January 2013 and February 2019. Thirty-eight client-owned dogs were included. Medical records were retrospectively evaluated for median overall survival time (MST), clinical and imaging responses. Prognostic factors on survival were researched in terms of signalment, clinical presentation, tumour imaging characteristics and response following RT. Finally, the RT’s impact on the dogs’ clinical signs and Qol were evaluated by the owners.

Results

The disease-specific MST was 698 days (95% CI: 598–1135). Survival at 1 and 2 years were respectively 74.2 ± 7.4% and 49.0 ± 9.8%. Initial clinical signs were related to survival, as well as tumour characteristics such as cystic-pattern, mass effect and Tumour/Brain volume ratio. No significant adverse effect or radiotoxicity was observed.

Conclusions

RT appears as a safe and effective treatment for canine intracranial gliomas, allowing long-term tumour control, improvement of life’s quality and management of associated clinical signs. The initial clinical signs and MRI characteristics (Tumour/Brain volume ratio, cyst-like lesion and mass effect) may help predict the prognosis.