CT of the canine middle ear for otitis media

Why otitis media is easy to miss

The bedside tests used to look for otitis media in dogs have clear limits.

• Ultrasound. In 32 dogs with otitis externa and/or otitis media (Classen et al., The Veterinary Journal, 2016), ultrasound of the tympanic bulla had a sensitivity of 21% and a specificity of 98% against CT or MRI. Video otoscopy performed much better, with 91% sensitivity and 98% specificity. The authors conclude that ultrasound should not replace cross-sectional imaging.
• The eardrum. In 60 cavalier King Charles spaniels with signs suggestive of primary secretory otitis media (Cole et al., Veterinary Dermatology, 2015), CT confirmed the disease in 43 (72%). A large, bulging pars flaccida was seen only in affected dogs (100% specificity), but in only 21 of 73 affected ears (29% sensitivity). When the pars flaccida was flat, none of the other tests (tympanometry, pneumotoscopy or bulla ultrasound) could replace CT.

Brachycephalic dogs: effusion is common

Fluid in the bulla is not always the cause of the signs. In a prospective study of brachycephalic dogs presented for airway surgery (Schuenemann et al., Tierärztliche Praxis Ausgabe K: Kleintiere/Heimtiere, 2022), the prevalence of incidental middle ear effusion on CT was 55 of 170 dogs (32%):

• only French bulldogs (35 of 66, 53%) and pugs (20 of 79, 25%) were affected
• all effusions that had cytology contained inflammatory cells
• bacteriology was positive in 34 of 76 ears (45%)

In these breeds, effusion should be weighed against the clinical signs rather than treated as the answer by default.

CT compared with MRI

CT and MRI answer different parts of the question, as an image essay on otitis media and its secondary lesions (Ludewig et al., Tierärztliche Praxis Ausgabe K: Kleintiere/Heimtiere, 2024) sets out:

	CT	MRI
Bulla wall involvement	More sensitive	Less sensitive
Abnormal content in the bulla	More effective at detection	Essential to characterise the material
Guiding sampling	Often easier
Soft tissues, meninges, brain and nerves	Not or only poorly shown	Clearly superior; shows central spread

Central spread can be silent. In 30 dogs with meningitis or meningoencephalitis from otitis media-interna (Moral et al., Veterinary Sciences, 2025):

• 96% were brachycephalic
• the neurological examination localised the lesion to the central nervous system in only 33% of dogs
• MRI showed no intracranial extension in 20% despite inflammatory cerebrospinal fluid (CSF)

The authors recommend MRI and CSF analysis when otitis media-interna is diagnosed, especially in chronic or recurrent cases and brachycephalic breeds.

In short: CT answers the bony and bulla-content question well. MRI is worth discussing when there are neurological signs, a suspected cholesteatoma, or chronic disease in a brachycephalic dog.

Cholesteatoma (tympanokeratoma)

Cholesteatomas are destructive keratinic masses of the middle ear that are often treated surgically (Coeuriot et al., Veterinary Radiology & Ultrasound, 2024). Recognising one before surgery is usually worth the effort, because CT signs of advanced disease relate to recurrence (Hardie et al., Veterinary Surgery, 2008).

• CT can miss it. In 11 dogs (13 ears) with cholesteatoma (Imai et al., Veterinary Dermatology, 2019), CT showed soft-tissue-like material in 12 bullae and expansion in only seven. The authors suggest that MRI is more sensitive than CT for identifying cholesteatoma.
• Diffusion-weighted MRI. Combined with apparent diffusion coefficient maps, it reached 92.6% sensitivity and 65% specificity in 62 ears.

Middle ear CT protocol at a glance

CT of the middle ear is aimed at the bulla wall and its contents, where CT is more sensitive than MRI. Separating cholesteatoma from a tumour depends partly on how the tissue enhances after contrast, as a CT study of middle ear cholesteatoma (Travetti et al., Veterinary Radiology & Ultrasound, 2010) describes.

What the radiologist looks at

• Effusion in context. In brachycephalic breeds, fluid in the bulla is common, so it is weighed against the clinical signs.
• The cholesteatoma pattern. In 11 dogs, cholesteatoma appeared as an expansile tympanic cavity mass with a mean attenuation of 55.8 ± 4.2 HU. The contents did not enhance appreciably, although four dogs showed ring enhancement. Bone changes included osteolysis, osteoproliferation, osteosclerosis and expansion of the bulla, with sclerosis or osteoproliferation of the temporomandibular joint and paracondylar process. Lysis of the petrous temporal bone can lead to intracranial complications.
• Signs linked to recurrence. In 20 dogs, 19 of which had CT, CT showed osteoproliferation (13 dogs), bulla lysis (12), bulla expansion (11), lysis of the squamous or petrous temporal bone (4) and enlarged lymph nodes (7).

How CT helps separate the main differentials, following the cholesteatoma CT study:

CT pattern	Points towards
Middle ear changes without routine enlargement of the tympanic cavity	Otitis media
Expansile, non-enhancing mass with osteoproliferation, lysis and temporomandibular joint changes	Cholesteatoma
Lysis of the bulla or petrous bone, soft-tissue swelling and marked contrast enhancement	Middle or inner ear tumour
Soft-tissue mass in the external acoustic meatus, with secondary middle ear involvement	Tumour of the external ear

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• A suspected mass still needs sampling. CT does not give a definitive diagnosis here, so cytology or histopathology is still needed.
• Otitis media-interna is a reason to consider MRI and CSF analysis, especially in chronic or recurrent cases and brachycephalic breeds.
• A suspected cholesteatoma may justify MRI, which the authors of the 11-dog series suggest is more sensitive than CT.
• Before surgery, remember that inability to open the mouth or neurological signs at admission, and lysis of any part of the temporal bone on CT, were risk factors for recurrence.

What to include when you request a middle ear CT report

• signalment: age, breed and sex, since brachycephalic dogs often have incidental effusion
• signs such as head tilt, ataxia, facial paralysis, or pain on opening or inability to open the mouth
• otoscopic findings, including whether the tympanic membrane is visible, intact or bulging
• duration of otitis externa, previous treatment and any previous ear surgery
• neurological signs that might suggest spread beyond the ear

How Veheri can help

Veheri’s radiologists report veterinary CT studies remotely for clinics, and we offer expert support for CT protocols, positioning and acquisition. For the feline version, see CT of the middle ear in cats, and for when to move to MRI, see when veterinary MRI is the right move.