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American Journal of Otolaryngology–Head and Neck Medicine and Surgery 33 (2012) 263 – 265 www.elsevier.com/locate/amjoto
Superior semicircular canal dehiscence: a possible pathway for intracranial spread of infection Renzo Manara, MDa,1 , Marco Lionello, MDb,1 , Cosimo de Filippis, MDb , Valentina Citton, MDa , Alberto Staffieri, MDb , Gino Marioni, MDb,⁎ a
Neuroradiology Unit, Padova Hospital, Otolaryngology Section, University of Padova, Italy Department of Medical and Surgical Specialties, Otolaryngology Section, University of Padova, Italy Received 23 March 2011
b
Abstract
Otogenic brain abscesses account for 31.4% of all cerebral abscesses: bone erosion due to coalescent otomastoiditis or cholesteatomas, osteothrombophlebitis, and hematogenous spreading are the most frequent pathways of infection. We briefly reported and discussed the first case of otogenic brain abscess due to infectious labyrinthitis that (likely) spread intracranially through a dehiscence of the superior semicircular canal. © 2012 Elsevier Inc. All rights reserved.
1. Introduction Bacterial brain abscesses are life-threatening infections diagnosed in approximately 1500 to 2500 patients each year in the United States [1]. Otogenic brain abscesses account for a large proportion of all cerebral abscesses (31.4%) [2], carrying a mortality rate of 3.8% [3]. Bone erosion due to coalescent otomastoiditis or cholesteatomas, osteothrombophlebitis, and hematogenous spreading are the most frequent pathways of infection; but the increasing quality of neuroradiologic examinations enables other, less common diffusion routes to be detected.
2. Case report A 53-year-old man was admitted to the Otolaryngology Section of Padova University complaining of a frontal headache, left ear fullness, and severe objective vertigo. Otoscopy was negative except for mild hyperemia of the left tympanic membrane (at the handle of the malleus). Neurovestibular examination revealed a spontaneous, right⁎ Corresponding author. Department of Medical and Surgical Specialties, Otolaryngology Section, University of Padova, Via Giustiniani 2, 35128 Padova, Italy. Tel.: +39 049 8218626; fax: +39 049 8213113. E-mail address:
[email protected] (G. Marioni). 1 The first 2 authors equally contributed to manuscript preparation. 0196-0709/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.amjoto.2011.05.006
beating, grade II horizontal nystagmus with an counterclockwise rotary component and rotation of the body's axis to the left on the Unterberger's stepping test. Pure tone audiometry identified left anacusis. The left tympanogram was A type. Laboratory investigations showed no leukocytosis (leukocytes, 6.08 × 109/L) and a normal C-reactive protein level (5.2 mg/L). A saline solution with 10% glycerol (250 mL once a day), pentoxifylline (500 mg in 100 mL of saline solution, twice a day), and betamethasone disodium phosphate (4 mg twice a day) was administered intravenously. The vestibular signs and symptoms persisted so the patient underwent contrast-enhanced magnetic resonance imaging (MRI) of the brain 10 days after the onset of his clinical symptoms, which disclosed a left temporal ring enhancing lesion (Fig. 1A) close to the petrous bone with marked enhancement of the contiguous dura mater. The lesion was characterized by severe perilesional edema and a necrotic core that was hyperintense on diffusion-weighted imaging (not shown), consistent with a pyogenic abscess. High-resolution sequences (slice 1-mm thick) showed a marked enhancement of the left membranous labyrinth (Fig. 1B) and a mild T2weighted hypointensity of the left cochlea and vestibule (Fig. 1C). Inflammatory changes in the tympanic cavity and a few petromastoid cells were also noted. Computerized tomography (CT) of the temporal bone confirmed the integrity of the tegmen tympani, a minimal involvement of contiguous petrous air cells and the superior semicircular
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Fig. 1. (A) Coronal contrast-enhanced, T1-weighted image showing a left temporal ring enhancing lesion consistent with brain abscess, with concomitant perilesional edema and marked enhancement of the underlying dura mater (small white arrows). (B) Axial thin contrast-enhanced, T1-weighted image: the cochlea shows moderate enhancement (white arrow). (C) Axial high-resolution T2-weighted image showing relative hypointensity of the left labyrinth (white arrow). (D) Coronal high-resolution CT image showing soft tissue in the middle ear, integrity of the tegmen tympani with air in the contiguous petrous bone cells, and the SSCD (white arrowhead). (E) Coronal contrast-enhanced, T1-weighted image on the same level as (A) showing decreased size of the brain abscess and reduction of the perilesional edema.
canal dehiscence (SSCD) (Fig. 1D). Intravenous antibiotic therapy was started (ceftriaxone 2 g twice a day and metronidazole 500 mg 3 times a day), and the patient slowly but constantly improved in terms of his vestibular symptoms, whereas his anacusis remained. The case was discussed with the neurosurgeon who ruled out any attempt to approach the brain abscess surgically. The patient was discharged after 6 weeks and continued with IM ceftriaxone 2 g twice a day. Brain MRI control showed a significant reduction in the size of the abscess (Fig. 1E) with the disappearance of the purulent component and a decrease in the perilesional edema, whereas enhancement of the labyrinth persisted. Plugging of the SSCD via a middle fossa approach was planned.
3. Discussion This case report shows that the superior semicircular canal might become a pathway for the intracranial spreading of infections. Cases of otogenic brain abscesses arising from middle ear infections and spreading through the SSCDs have not been reported to date, but such an occurrence may be overlooked in cases with concomitant petrous bone inflam-
mation. In our patient, the infection's diffusion through the labyrinth via an SSCD was supported by clinical, MRI, and CT findings, that is, (1) anacusis and vertigo at onset demonstrate the primary involvement of the left labyrinth; (2) the location of the brain abscess, close to the petrous bone, and the enhancement of the labyrinth and overlying dura mater supported the otogenic origin of the lesion; and (3) the absence of any tegmen tympani erosion or inflammatory involvement of the underlying petrous bone air cells make this route of infection unlikely. Superior semicircular canal dehiscence is not a rare finding because it is detected on CT scans in 3.6% of individuals [4]; this bone anomaly is known to cause several clinical conditions such as typical vestibular symptoms, autophony, hyperacusis to body sounds, hearing loss, and aural pressure tinnitus [5]; but its role as a locus minoris resistentiae for the spread of infection had not yet been considered. In conclusion, we reported the first case of otogenic brain abscess due to infectious labyrinthitis that (likely) spread intracranially through a dehiscence of the superior semicircular canal. This case broadens the spectrum of pathways of infection leading to otogenic brain abscess. A focused neuroimaging protocol for otogenic brain abscesses is warranted to demonstrate or exclude any concomitant
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involvement of the labyrinthine structures or presence of congenital bone anomalies.
Acknowledgments The authors thank Frances Coburn for revising the final English version of this manuscript. The authors have no conflict of interest to declare. This study was supported by a research grant (no. 60A07-4404/09 G.M.) from the University of Padova, Italy. All authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
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References [1] Mamelak AN, Mampalam TJ, Obana WG, et al. Improved management of multiple brain abscesses: a combined surgical and medical approach. Neurosurgery 1995;36:76-85 [discussion 85-6]. [2] Prasad KN, Mishra AM, Gupta D, et al. Analysis of microbial etiology and mortality in patients with brain abscess. J Infect 2006;53:221-7. [3] Yen PT, Chan ST, Huang TS. Brain abscess: with special reference to otolaryngologic sources of infection. Otolaryngol Head Neck Surg 1995;113:15-22. [4] Crovetto M, Whyte J, Rodriguez OM, et al. Anatomo-radiological study of the superior semicircular canal dehiscence radiological considerations of superior and posterior semicircular canals. Eur J Radiol 2010;76:167-72. [5] Minor LB. Clinical manifestations of superior semicircular canal dehiscence. Laryngoscope 2005;115:1717-27.
