26 Dec, 2018

Role of Radiology in Ear Discharge - Dr A Anbarasu

Dr A Anbarasu
Caran Diagnostic Imaging, Coimbatore
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Fluid Discharge from the ear is a common problem in both children and adults. The discharge can be pus, blood, clear fluid or serous fluid; sometimes combinations can happen such as blood stained pus discharge.

Clinical history:

Pus discharge is usually suggestive of infection at external ear, middle ear or both; this can be acute or chronic and usually associated with tympanic membrane perforation or inflammation. Clinical assessment is limited to otoscopy visualisation of external ear, tympanic membrane and assessment for deafness and vertigo.

One important aspect of external otitis is malignant otitis externa; reported first by Meltzer 1959. The term “Malignant Otitis Externa” first used by Chandler in 1968 (7 of 13 patients died); the current tem is necrotising otitis externa (NOC); this is a necrotising osteomyelitis of temporal bone characterised by otitis externa and pain, commonly in immuno-compromised patients usually due to Pseudomonas aeruginosa. Most patients are diabetic.

Serous fluid discharge is commonly secondary to mild external ear inflammation or secondary to serous middle ear effusion which can exit through a perforated tympanic membrane. This is occasional, may resolve itself and therefore may not reach the clinician for further assessment – unless there are associated symptoms of vertigo, deafness or pain. Clinical inspection of the EAC is needed to exclude, local mild inflammation, wax, keratosis or foreign body.

Blood discharge is usually associated with trauma or foreign body. Most traumatic haemorrhages from ear are associated with fractures which need to be confirmed with imaging. Sometimes trauma history may not be available from the patient e.g.: alcohol related falls. Blood staining of external ear is the clinical clue; this again can be associated with hearing loss, tinnitus, vertigo and facial nerve palsy. Also note in external otitis/ otitis media blood can be mixed with pus.

Clear fluid discharge is suspicious of cerebrospinal fluid leak; this is usually associated with fracture of middle cranial fossa floor and tegmen with associated tympanic membrane perforation. Occasionally, erosion of tegmen secondary to infective or neoplastic process.

ENT surgeon / General Physician, carefully evaluates the clinical presentation of the patient by asking pertinent questions; following clinical examination, the request for imaging is made, when there is a need for further evaluation of the other structures and extent of the disease.

What Imaging modality?

Radiography, Ultrasound, CT, MRI, Nuclear Medicine tests are the relevant tests available for a patient with ear discharge. Each one has its own strengths and limitations; with advances in research and technology, few indications for certain tests are becoming obsolete.

Radiographs:

Traditionally Stenver’s view has been used for evaluation of the mastoid pneumatisation, sinus plate and dural plate intactness. However, further information is limited; in view of reduced frequency of radiography, the interpretation experience is increasingly limited.

Ultrasound:

Ultrasound has limited role to play in ear discharge; few patients can have associated neck lumps (e.g.: ear discharge with neck lymphadenopathy), for which, ultrasound, is best the first modality, that help in evaluation and confirmation of the diagnosis.

Computed Tomography (CT Scan) (High resolution CT / Pre and post contrast CT scan/ CT cisternography)

HRCT of temporal bone is the main stay of temporal bone evaluation. In case of pus discharge – presence of – soft tissue in the middle ear, usually intact ossicles, fluid level at mastoid cells, will help to diagnose acute otomastoiditis. Coalescent mastoiditis is when the cells fuse together due to break down of walls and formation of small cavities within mastoid filled with pus (fig 1). In chronic otomastoiditis, there is sclerosis of the mastoid cells. Calcification can occur within the middle ear soft tissue, suggestive of tympanosclerosis.

If there is erosion of ossicles, scutum, tegmen or sinus plate, coexistent cholesteatoma needs consideration (fig 2); however, these changes can occur with infection/inflammation occasionally without cholesteatoma.

FIG2

 

The extent of disease into various recesses within middle ear is also easily assessed with MDCT with HRCT reconstructions (fig 3).

(Fig 3: extensive otomastoiditis with complete filling of middle ear; ossicular chain were intact)

 

Otitis externa can occur without middle ear disease; CT can show erosion of external ear bony canal margins which raises the possibility of necrotising otitis externa (NOE) (previously known as malignant otitis externa). Contrast enhanced CT should be done, in this situation, to assess the extent of disease along the infratemporal fossa, carotid canal, jugular fossa and sometimes posterior fossa. Severe pain is an important clinical feature of NOE.

External bony canal fractures (fig 4) should be looked for in patients with bloody discharge; ossicular chain dislocation, types of fractures - longitudinal, transverse, oblique pattern (fig 5), blood in the middle ear and external ear, air pocket within internal ear are some of the features to be looked for in the HRCT.

(Fig 5 a&b: Post trauma; blood at external ear (a) and middle ear; longitudinal fracture through mastoid (b))

In case of CSF leak, tegmen defect or fracture is usually present; CT cisternogram should be done followed by coronal position CT to appreciate intrathecal contrast (CSF leak) into the middle ear; CSFcomes out as ear discharge when there is associated tympanic membrane perforation – clinically seen as CSF otorrhea. Other causes include, erosion of inner ear structures by infection, inflammation, cholesteatoma, tumour, creating fistulous communication to middle ear and external ear (fig 6 a,b,c,d)

Fig 6 c&d

(Fig 6a,b,c,d: patient of 25 years age presented with CSF otorrhea for the first time; otoscopy was suspicious of cholesteatoma. HRCT show large lesion at middle ear and eroding inner ear structures up to IAC fundus (a&b); MRI shows CSF signal lesion, connecting to IAC medially and external ear laterally. Histology – congenital cholesteatoma with inner ear fistula)

 

It is important not to misinterpret simple effusion as otomastoiditis; no specific CT features to differentiate these two available during initial presentation; often clinical assessment is more accurate in this settings.

 

Magnetic Resonance Imaging (MRI)

 

The role of MRI is usually to answer a few questions, which are raised by CT; the intracranial involvement – meningeal disease, brain edema / collection, infratemporal fossa edema are better assessed by MRI. Herniation of brain tissue into tegmen defect and CSF leak to middle ear are also shown better with MRI (fig 6 c,d); various sequences allow differentiation of  brain tissue, meningeal layers, fluid and middle ear soft tissue.

Nuclear Medicine:

Bone scan with Tc99m MDP, has a role in patients with necrotising otitis externa; bone scan is sensitive in assessing initial involvement and extent of bone disease in infection; this also helps in assessing the early the response to treatment, Gallium scan is more specific recurrent disease and persistent infection as all other modalities including bone scan may show long standing changes. In specific cases, these investigations can be useful in decision with regards to dosage and duration of antibiotic treatment in NOC (fig 7 a,b,c,d).

(Fig 7 a,b,c,d – Necrotising otitis externa: CT at presentation showed erosion of external ear bony wall with extend of disease into TMJ causing marginal erosion (a); 4 month later, the disease is spreading to erode clivus, jugular fossa, carotid canal margins – skull base osteomyelitis (b); contrast enhanced CT show abscess formation at periverterbral space at the level of nasopharynx with extensive soft tissue disease (c); Tc99m MDP bone scan done 2 months later persistent disease with accumulation of tracer at left temporal bone including petrous apex and TM joint.

Conclusion:

Fluid coming out of ear needs proper clinical assessment and stratification of patients based on nature of fluid and clinical signs; most cases, should be followed by appropriate imaging; this helps in achieving correct diagnosis and guide proper management.