June 2017
A 70-year-old man with uncontrolled type 2 diabetes, reported CVA with residual complete right facial paralysis, and recent mastoidectomy presents with chronic headache and asymmetry of oropharynx on exam.
Skull Base Osteomyelitis with Resultant Cranial Neuropathies
- Background:
- Skull base osteomyelitis is seen most frequently in elderly patients in the setting of diabetes or other immunocompromise.
- Skull base osteomyelitis is most commonly a complication of malignant otitis externa. While malignant otitis externa typically is confined to the temporal bone, involvement of the sphenoid, occiput, and clivus may occur. This is referred to as central or atypical skull base osteomyelitis.
- Cranial neuropathies may result from extension into the skull base. Involvement of the stylomastoid foramen results in neuropathy of cranial nerve VII, while involvement of the jugular foramen and hypoglossal canal may result in neuropathy of cranial nerves IX, X, XI, and XII.
- Of note, cranial neuropathies due to skull base osteomyelitis may resolve with appropriate antibiotic treatment.
- Clinical Presentation:
- While a history of prior stroke was reported, imaging revealed the brain parenchyma to be intact. The patient’s facial paralysis more likely represents sequela of malignant otitis externa or postoperative complication related to subsequent mastoidectomy.
- Additionally, the patient demonstrated deafness in the right ear, paralysis of the right vocal cord, and dysphagia. These findings can be accounted for by involvement of cranial nerves VIII, X, and XII, respectively.
- Key Diagnostic Features:
- CT is commonly used initially to evaluate osseous destruction; however, osseous involvement may not be evident until more than 30% bone loss has occurred. Therefore, initial findings may be limited to obliteration and enhancement of adjacent fat planes surrounding the central skull base and retrocondylar fat.
- MRI with limited field of view centered on the central skull base provides a more comprehensive evaluation of marrow signal abnormality, as well as surrounding soft tissue involvement. T1WI will demonstrate replacement of the normal high signal marrow and associated enhancement on postcontrast images.
- In addition, MRI is invaluable in demonstrating associated complications, including dural enhancement, septic cavernous sinus thrombosis, intracranial involvement, petroclival abscess, and spread to the prevertebral space.
- Differential Diagnoses:
- The primary differential consideration is malignancy and includes nasopharyngeal carcinoma, lymphoma, melanoma, and neuroendocrine tumors.
- Differentiation between malignant and infectious etiologies on the basis of imaging is difficult.
- Diagnostic uncertainty may necessitate biopsy for pathologic and microbiological analysis
- Treatment:
- Osteomyelitis usually responds to medical management, with initiation of broad-spectrum antibiotics upon presentation and continuation of antibiotics for at least 4–6 weeks. Identification of the offending organism with blood culture ± bone or tissue biopsy allows for the antibiotic coverage to be narrowed to the specific organism.
- Surgical intervention is necessary when there is inadequate response to antibiotics, grossly necrotic tissue, foreign body, abscess formation, and wound closure in cases with an open wound.
