Skull Base Osteomyelitis: A Comprehensive Imaging Review

Abstract

Skull base osteomyelitis is a relatively rare condition, generally occurring as a complication of advanced otologic or sinus infection in immunocompromised patients. Skull base osteomyelitis is generally divided into 2 broad categories: typical and atypical. Typical skull base osteomyelitis occurs secondary to uncontrolled infection of the temporal bone region, most often from necrotizing external otitis caused by Pseudomonas aeruginosa in a patient with diabetes. Atypical skull base osteomyelitis occurs in the absence of obvious temporal bone infection or external auditory canal infection. It may be secondary to advanced sinusitis or deep face infection or might occur in the absence of a known local source of infection. Atypical skull base osteomyelitis preferentially affects the central skull base and can be caused by bacterial or fungal infections. Clinically, typical skull base osteomyelitis presents with signs and symptoms of otitis externa or other temporal bone infection. Both typical and atypical forms can produce nonspecific symptoms including headache and fever, and progress to cranial neuropathies and meningitis. Early diagnosis can be difficult both clinically and radiologically, and the diagnosis is often delayed. Radiologic evaluation plays a critical role in the diagnosis of skull base osteomyelitis, with CT and MR imaging serving complementary roles. CT best demonstrates cortical and trabecular destruction of bone. MR imaging is best for determining the overall extent of disease and best demonstrates involvement of marrow space and extraosseous soft tissue. Nuclear medicine studies can also be contributory to diagnosis and follow-up. The goal of this article was to review the basic pathophysiology, clinical findings, and key radiologic features of skull base osteomyelitis. ABBREVIATIONS: ASBO ¼ atypical skull base osteomyelitis; EAC ¼ external auditory canal; Ga-67 ¼ gallium-67 citrate; IgG4 ¼ immunoglobulin G4; Tc99m MDP ¼ technetium Tc99m methylene diphosphonate; NEO ¼ necrotizing external otitis; SBO ¼ skull base osteomyelitis; TSBO ¼ typical skull base osteomyelitis S kull base osteomyelitis (SBO) is a rare, potentially life-threatening infection that can present a diagnostic challenge clinically and radiologically. [1][2][3][4] While reports differ in terminology, there are generally 2 categories of SBO: typical and atypical. Typical SBO (TSBO) is the most common and classically occurs in elderly patients with diabetes as a result of necrotizing external otitis (NEO) caused by Pseudomonas species. (Fig 1). 1,3 Atypical SBO (ASBO), also called central SBO, predominantly involves the basisphenoid and basiocciput and occurs without preceding otologic infection (Fig 2). 2,5 Recognition of SBO is increasing, and it is clear that radiologic evaluation plays a critical role in diagnosis and management. The goal of this article was to review the pathophysiology, clinical presentation, and detailed radiologic findings using multiple modalities including CT, MR imaging, and nuclear medicine.

Extensive skull base osteomyelitis, devastating complication of otitis externa: A case report and review of the literature

“…The typical form of SBO related to otitis externa or mastoiditis presents with severe otalgia, pain in the involved temporal, parietal, post-auricular and retroorbital areas, aural fullness and purulent otorrhea with fever. The clinical examination may find induration of pinna, mastoid cutaneous fistula or preauricular cellulitis with fibrotic granulation tissue or a polyp in the EAC particularly at the level of bony-cartilaginous junction [3,4,7,8]. The atypical form can be revealed by unremitting headaches but the absence of localized and evident infection poses diagnosis challenges [3,8].…”

“…The clinical examination may find induration of pinna, mastoid cutaneous fistula or preauricular cellulitis with fibrotic granulation tissue or a polyp in the EAC particularly at the level of bony-cartilaginous junction [3,4,7,8]. The atypical form can be revealed by unremitting headaches but the absence of localized and evident infection poses diagnosis challenges [3,8]. Indeed, on Singh et al [9] study about 10 patients treated for atypical SBO, the main clinical symptom was a vague dull headache with one or more cranial nerve palsy(s) while the radiological examination showed clival involvement in all the cases, concluding that the suspicion of atypical SBO should be raised in front of non-specific symptoms of headaches with cranial nerve palsy even with no evident signs of otological or rhinological infections especially in immune-compromised patients.…”

“…The progression of SBO can lead to cranial neuropathies [8]. The facial nerve is the most common and first cranial nerve involved when the infection spreads subtemporally at the stylomastoid foramen [3] with a rate reported by Chandler et al [10] at 46%, presented by facial palsy or facial twitching suggestive of facial canal dehiscence [4].…”

“…Only early diagnosis can prevent central nervous system complications but it can be difficult and is then, often delayed [3,8]. It is based on clinical, radiological and laboratory findings but the absence of infectious symptoms and normal blood tests is not uncommon in immune-compromised patients [1].…”

“…CT scan best demonstrates cortical and trabecular bone erosion or periosteal remodelling which is relatively a late phenomenon, soft tissue swelling with thinning of the fat planes and the extent of disease even if the demineralization in only seen if ≥ 30% [1,4,8]. But it is insufficient to represent intracranial extension, bone marrow involvement, and to measure treatment response measured by bone remineralization because it rarely returns to normal [1,3,4].…”