Comparison of medical and/or surgical management of 23 cats with intracranial empyema or abscessation

Objectives Feline intracranial abscessation or empyema is infrequently reported in the veterinary literature. To date, the largest study is based on a population of 19 cats with otogenic infection. The aim of this study was to review a larger population of cats with intracranial empyema from multiple aetiologies and document their signalment, imaging findings, treatment protocols (including medical and/or surgical management) and to compare outcomes. Methods Cases presenting to a single referral centre over a 10 year period with compatible history, neurological signs and imaging findings consistent with intracranial abscessation and empyema were reviewed retrospectively. Results Twenty-three cats met the inclusion criteria. Advanced imaging (CT and/or MRI) was performed in 22/23 cats; one case was diagnosed via ultrasound. Ten cases underwent medical and surgical management combined, 10 underwent solely medical management and three were euthanased at the time of diagnosis. Short-term outcome showed that 90% of surgically managed and 80% of medically managed cats were alive at 48 h post-diagnosis. Long-term survival showed that surgically managed cases and medically managed cases had a median survival time of 730 days (range 1–3802 days) and 183 days (range 1–1216 days), respectively. No statistical significance in short- or long-term survival (P >0.05) was found between medically and surgically managed groups. Conclusions and relevance Feline intracranial abscessation and empyema are uncommon conditions that have historically been treated with combined surgical and medical management. This study documents that, in some cases, intracranial abscessation and empyema can also be successfully treated with medical management alone.

thickness for brain and 1-2mm slice thickness for head sequences. Pre-and post-contrast 123 exams were performed, with bone and soft tissue recons. All MRI images were obtained 124 using a 1.5 Tesla Intera System (Philips Medical Systems). Each cat had a minimum series 125 including pre-and post-gadolinium contrast T1-weighted (T1W) series and T2-weighted 126 Cats were subsequently divided into solely medically treated or combined surgically and 138 medically treated groups. Only those cases treated via craniectomy were defined as 139 surgically treated, cases undergoing any other form of surgery (e.g. ventral bulla 140 osteotomy) were therefore categorised as medically managed. 141 Information regarding outcome was obtained via telephone consultation with the 143 referring veterinarian and/or owner, combined with the referring vet clinical records and 144 findings of re-examination appointments at the RVC. Short-term outcome was reviewed 145 at 48 hours (h) and one month after diagnosis, longer-term outcome was assessed at three 146 and six months. Outcome was classified as alive or dead, but where available, survival 147 was further categorised with a 1-3 grading system alongside neurological examination 148 findings. The grading system is as follows; Grade 1 was given if cats returned to being 149 neurologically normal, Grade 2 was defined as persistent mild neurological deficits that 150 did not affect the normal ambulation and behaviour of the cat, Grade 3 was defined as 151 persistent neurological abnormalities that significantly affected the patients' ability to 152 ambulate and display normal behaviours. 2008 and August 2017. One cat was excluded as initial diagnostics and surgery were 163 performed at an alternative referral centre, a second cat was excluded due to a lack of pre-operative imaging. A further two cats were excluded as they failed to fulfil the 165 imaging criteria of IA and/or IE. Twenty-three cats were included in the study 166 population. 167

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The included cats had a median age of 7.4 years at presentation (range 7 months-16 years) 169 and had a male predominance with 15 neutered males (65.3%), two entire males (8.7%), an absent menace response (Table 1). Seizure activity was infrequently reported; two cats 207 exhibited generalised seizures and one partial seizures prior to referral. 208 with IE, four intra-axial IA and three had findings compatible with IA and IE (Table 2). 215 Distribution was classified as forebrain (13) Of the surgically managed group, most (90%) cats had a good short-term prognosis 307 (survived 48 h post-operatively). One case failed to regain spontaneous ventilation after 308 surgery and was euthanised. All 9/10 remaining cats were alive 6 months post-309 operatively and had a Grade 1 neurological status. The median survival time for 310 surgically managed cases was 730 days (range 1-3802 days). One cat was euthanised 7 311 years after diagnosis due to development of seizures and deterioration to status 312 epilepticus; repeat imaging was not performed prior to euthanasia. 313

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The medically managed group had a similar short-term prognosis, with 80% of cases 315 surviving the first 48 h after diagnosis. Of the two cases that did not survive, one had cardiopulmonary arrest whilst receiving treatment and another was euthanised after 24 317 h of medical therapy due to financial constraints. Six-month survival information was 318 available for the eight remaining medically managed cats. Six out of 8 cats had good long-319 term outcome, all of which were reported to be neurologically normal (grade 1). 320 Medically managed cases had a median survival time of 183 days (range 1-1216 days). 321

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It is important to note that two cats, one of each treatment group, were still alive at the 323 time of writing this paper.  systemic response to intracranial infection; it is important therefore that IA and IE is still 355 considered as a differential in normothermic cases without peripheral neutrophilia . 356 As with other case reports, CSF analysis was rarely undertaken, likely due to a greater 358 risk of complications when performing this procedure in cases with increased intracranial 359 pressure. 5 When performed, CSF results consistently demonstrated neutrophilic 360 inflammation and were diagnostic (exhibited intracellular bacteria or had positive culture 361 results) in two cases with empyema. Intracellular organisms are less frequently seen with 362 intra-axial abscesses unless they have ruptured into the subdural space. 8 When available, 363 CSF analysis provides valuable diagnostic information. It may be argued that these 364 results are of more use in medically managed cases, as intra-operative findings and the 365 ability to culture direct swabs taken at the time of craniectomy may make CSF findings 366 redundant in surgical cases. 367

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Reports of predisposition to both aerobic and anaerobic bacteria exist within the 369 literature. 8 A mixed cohort of both aerobic and anaerobic isolates were identified in this 370 study. This likely reflects the underlying aetiology of the IA and/or IE as both OMI and 371 cat bite abscesses can yield polymicrobial growth. 20,21 In this study only 33% of CSF 372 samples and 67% of surgical swabs yielded positive culture results; this finding is 373 consistent with the existing literature. 22 A likely explanation for the high incidence of 374 negative culture results may be that many cases were exposed to antibiotics prior to