Diagnosing necrotizing external otitis on CT and MRI: assessment of pattern of extension

Abstract

Background and purpose Necrotizing external otitis (NEO) is a serious complication of external otitis. NEO can be classified according to—anterior, medial, posterior, intracranial, and contralateral—extension patterns. Currently there is no consensus on the optimal imaging modality for the identification of disease extension. This study compares NEO extension patterns on MR and CT to evaluate diagnostic comparability. Methods Patients who received a CT and MR within a 3-month interval were retrospectively examined. Involvement of subsites and subsequent spreading patterns were assessed on both modalities by a radiologist in training and by a senior head and neck radiologist. The prevalence of extension patterns on CT and MR were calculated and compared. Results All 21 included NEO cases showed an anterior extension pattern on CT and MR. Contrary to MR, medial extension was not recognized on CT in two out of six patients, and intracranial extension in five out of eight patients. The posterior extension pattern was not recognized on MR. Overall, single anterior extension pattern (62%) is more prevalent than multiple extension patterns (38%). Conclusion All anterior NEO extension pattern were identified on CT as well as MR. However, the medial and intracranial spreading patterns as seen on MR could only be identified on CT in a small number of patients. The posterior spreading pattern can be overlooked on MR. Thus, CT and MR are complimentary for the initial diagnosis and work-up of NEO as to correctly delineate disease extent through the skull base.

Current management of skull base osteomyelitis

“…1) [25,26]. Van der Meer et al found that medial or intracranial spreading patterns can be best identified with MRI, whereas posterior spreading patterns solely based on cortical destruction of the mastoid and temporal bone were solely found by CT [27 ▪ ].…”

Management and long-term comorbidities of patients with necrotizing otitis externa

“…MRI is superior in evaluating soft-tissue extent, bone marrow involvement, and intracranial complications. Disease extension, progression, and complications during follow-up are best evaluated with MRI [ 13 , 14 ]. However, MRI findings always lag behind the clinical improvement.…”

Skull base osteomyelitis imaging

“…A retrospective study of NEO patients described five different patterns of spread- anterior (most common, involving temporal bone and TMJ), medial (sphenoid bone, clivus, petrous apex, jugular foramen), posterior (mastoid temporal bone), intracranial and contralateral [40 ▪ ]. Different modalities were complementary in identification of these extension patterns, e.g., anterior pattern seen on both MR and CT, medial and intracranial better seen on MR and posterior pattern on CT [40 ▪ ].…”