Stenotrophomonas skull base osteomyelitis presenting as necrotizing otitis externa: Unmasking by CT and MRI-case report and review

Abstract

Necrotizing or malignant otitis externa in patients presenting with mild clinical findings can pose as a tip of the iceberg; computed tomography (CT) and/or magnetic resonance imaging (MRI) unveils the clinical-imaging discrepancy and unmasks the presence of skull-base osteomyelitis (SBO). Pseudomonas aeruginosa is the most common causative pathogen of SBO, followed by fungal and other rare bacterial organisms. This report presents a rare case in an elderly diabetic patient, where the pathogen Stenotrophomonas maltophilia was isolated. There have been no previous reported cases in the literature of SBO caused by this pathogen. The hallmark of SBO on computed tomography or magnetic resonance imaging is soft tissue inflammatory changes under the central skull base with associated bone erosion. This may result in the peculiar appearance of the "Ovoid Gap" sign. SBO can be due to nonotogenic sources, namely: sinogenic, rhinogenic, pharnygogenic, or odontogenic infections. Low threshold for imaging is advised in immunosuppressed and elderly diabetic patients.

Keywords: Malignant otitis externa; Necrotizing ootitis externa; Skull base osteomyelitis; Stenotrophomonas.

Fig. 1

Axial CT soft tissues (A) and High resolution Temporal bone images (B-D). Confluent inflammatory prevertebral and posterior nasopharyngeal soft tissue thickening along the skull-base (A-white contours). Central skull-base erosion of petrous and occipital bones (B-arrows). Note erosive holes in inferior mastoid temporal bones (C-arrows). Bilateral “Ovoid” appearing gap between the bones at the central skull-base due to expansile and erosive soft tissue thickening (C-white contours). Left otomastoid and external ear nonerosive opacification (D-arrows).

Fig. 2

Axial (A), Sagittal (B), Coronal (C) contrast enhanced T1 and ADC maps skull-base. Diffuse crossed diffuse enhancing soft tissue thickening (A-C-arrows) in the preclival, posterior nasopharyngeal, upper parapharyngeal soft tissues under the skull base as well as left masticator space (A-left lateral arrow) and peridental involvement (B-arrows). Note facilitated diffusion on ADC maps (D-arrows) favoring inflammation against hypercellularity (of neoplasm) and excluding focal abscess.

Fig. 3

Axial T2 (A), fat saturated contrast enhanced T1(B), axial 3D TOF MRA source (C), and Diffusion weighted images (D). Initial isolated submucosal nasopharyngeal inflammatory focus (A-arrow) in a poorly controlled diabetic patient (other than the index case). Follow-up in few weeks show extensive crossed inflammatory soft tissue changes under the skull base with necrotic foci (B-anterior arrows). Note focal intracranial posterior fossa extension via bone erosion (B-small posterior arrow). Carotid sheath involvement with ICA encasement and eventual occlusion (C-arrow) and multiple acute embolic infarcts in ICA distribution.