Occult otitis media in dogs with chronic otitis externa – magnetic resonance imaging and association with otoscopic and cytological findings

Abstract

Background Identification of perpetuating factors, such as otitis media (OM), is important for the successful management of canine chronic otitis externa (OE). Hypothesis/Objectives Occult OM can occur in cases of chronic OE; a focused magnetic resonance imaging (MRI) examination is a useful tool in their management. Animals One hundred twenty one client‐owned dogs presented for investigation and treatment of chronic OE between 2009 and 2018. Methods and materials Mixed retrospective (74 dogs) and prospective (47 dogs) study of chronic OE cases without neurological signs, describing the MRI, otoscopic and cytological findings; comparing cases with and without MRI evidence of OM. Results A total of 123 MRI studies were analysed (two dogs scanned twice). A short, focused MRI scan allowed detection of inflammation of the mucosal bulla lining as well as excellent discrimination between avascular material and vascularised soft tissue in the tympanic cavity. OM was found in 41 of 197 (21%) ears with chronic otitis externa. On otoscopy, the tympanic membrane was intact in six of 41 ears (15%), ruptured in 16 of 41 (39%) and not visible in 14 of 41 (34%) [no data in five of 41 (12%)]. Analysis of cytological findings showed that the presence of rods was only associated with an increased likelihood of OM when found together with inflammatory cells. Conclusions and clinical importance Occult OM is a not uncommon finding on MRI of dogs with chronic OE. A targeted MRI study (“bulla mini‐scan”) may be useful as part of the clinical investigations.

Malassezia otitis unresponsive to primary care: outcome in 59 dogs

“…Otitis cases in this study are unlikely to represent the wider population of dogs with chronic Malassezia otitis, in view of selection bias inherent to a referral service and for dogs generally amenable to home treatment. However, in terms of age profile and unilateral versus bilateral otitis presentation, the cases in this study match other studies of chronic otitis 17,30 and also field studies that have not specifically enrolled chronic cases 9,20,21 . Together, spaniel and retriever breeds accounted for over half of the affected dogs in this study and also those in the hospital denominator population with otitis, similar to recent findings from a European otitis treatment intervention study 10 .…”

“…The frequency of Mal OE/OM in the present study, however, is comparable to reports of OM diagnosed in dogs with undefined, chronic OE using CT 35 and MRI 17 imaging. However, both imaging modalities may fail to diagnose cases of early OM when there are only minor pathological findings in the tympanic cavity 17,36,37 . It is notable that only four of 14 ears judged by the clinician to have Mal OE/OM in this study, based on video‐otoscopy and bulla lavage, had evidence of soft tissue attenuating material in the tympanic bulla on CT imaging.…”

“…This procedure carries the potential for iatrogenic contamination of yeast from the ear canal into the tympanic cavity and thereupon false diagnosis of MalOE/OM. 33,34 The frequency of MalOE/OM in the present study, however, is comparable to reports of OM diagnosed in dogs with undefined, chronic OE using CT 35 and MRI 17 imaging. However, both imaging modalities may fail to diagnose cases of early OM when there are only minor pathological findings in the tympanic cavity.…”

“…However, both imaging modalities may fail to diagnose cases of early OM when there are only minor pathological findings in the tympanic cavity. 17,36,37 It is notable that only four of 14 ears judged by the clinician to have MalOE/OM in this study, based on video-otoscopy and bulla lavage, had evidence of soft tissue attenuating material in the tympanic bulla on CT imaging. Integrity of the tympanic membrane was not a reliable indicator for status of middle ear disease (as proposed by Cole in 1998) and neither was absence of neurological signs 38 or duration of ear disease.…”

“…Diagnosis of Mal OE was assigned based upon recorded diagnosis of OE and an absence of middle ear pathological findings on CT imaging. A diagnosis of Mal OE/OM required cytological detection of yeast microbes within debris aspirated directly from the middle ear, in the presence or absence of soft tissue attenuating material in the middle ear on CT imaging 17 . If Mal OE was associated with bacterial or sterile OM in the same ear, this ear was excluded from the study.…”