<div>Ethical Approval: Exempt; Patient Permission Obtained</div><div>Word count: 1020</div><div>Figures and Tables: 2</div><div>Journal: Clinical Case Reports</div><div>Article Type: Case Report</div><div>Keywords: Ear, Nose, and Throat, and Infectious Diseases</div><div>Consent: Written and verbal patient consent was obtained for the
publication of the case report. Written consent is available upon
request.</div><div>Data Availability: Data is available upon request to authors.</div><div>Conflict of Interests: None</div><div>INTRODUCTION</div><div>Skull base osteomyelitis (SBO) involves an inflammatory process
implicating the temporal, sphenoid, and occipital bones that commonly
presents with severe otalgia, purulent otorrhea, headache, and
conductive deafness from Eustachian tube dysfunction<sup>1</sup>. Left untreated, SBO leads to significant mortality
with the development of meningitis, intracranial abscess, and venous
sinus thrombosis <sup>2</sup>. Treatment requires an extended
course of culture-directed antibiotics and possible surgical debridement<sup>3</sup>. SBO may present similarly to malignancy thereby
presenting a diagnostic dilemma. Herein, we present a case of SBO with
extensive bony erosion diagnosed by computed tomography (CT) guided core
biopsy and complicated by cerebral venous sinus thrombosis in a patient
lacking traditional risk factors.</div><div>CASE</div><div>An otherwise healthy 70-year-old male with a history remarkable for 30
pack-years of cigarette smoking presented to the emergency department
(ED) with worsening right-sided otalgia and otorrhea. The patient
initially began experiencing otalgia three months before presentation
after undergoing a dental procedure. The otalgia improved slightly with
intermittent antibiotics but became increasingly severe prompting ED
presentation. On arrival, he also reported frontal-to-right temporal
headaches and worsening dysphagia, initially to solids and progressing
to include liquids resulting in a 20-pound weight loss over the span of
three weeks. He denied any changes to his hearing or vision.</div><div>On examination, the patient had a hoarse voice, right palatal weakness,
and tenderness along the right lateral neck and peri-auricular region.
The tympanic membranes (TM) were intact. There was scant otorrhea with
mild edema of the right external auditory canal (EAC). There was no
facial weakness, and the tongue was midline. He was afebrile and his
labs were notable only for mildly elevated white blood cell count (13.51
x 10<sup>9</sup>/L) and C-reactive protein (15.34 mg/L).</div><div>Computed tomography (CT) of the head and neck was obtained and
demonstrated a significant infiltrating soft tissue mass of the right
upper neck and skull base (Figure 1). There was accompanying bony
destruction and invasion of the occipital bone with extension to the
right hypoglossal canal, jugular bulb, and stylomastoid foramen.
Magnetic resonance imaging (MRI) T1 Dixon sequence imaging demonstrated
hyperintensity at the right skull base with infiltration of the
occipital bone (Figure 1). The right TM was moderately thickened with a
narrowed EAC (Figure 2). Mild meningeal enhancement and thickening were
present without findings of intracranial abscess.</div><div>Imaging findings were concerning for skull base infectious process or
invading malignancy. The patient was initially started on empiric
intravenous vancomycin, cefepime, voriconazole, and metronidazole.
Corticosteroids were also given which improved cranial nerve dysfunction
and lateral neck pain. A CT-guided core biopsy of the soft tissue mass
was obtained. Pathology was negative for neoplastic processes while
aerobic culture grew pan-sensitive <i>Pseudomonas aeruginosa</i> . The
antibiotic regimen was subsequently narrowed to culture-directed
cefepime.</div><div>The patient’s hospitalization was complicated by sigmoid and transverse
sinus thrombosis, upper gastrointestinal bleeding, and sepsis. Venous
thrombosis was diagnosed by magnetic resonance venography, and the
patient was started on a low-intensity intravenous heparin, which was
later transitioned to oral anticoagulation. After appropriate
interventions, the patient was safely discharged to home with a
peripherally inserted central catheter (PICC). Oral anticoagulation and
intravenous cefepime was continued at discharge.</div><div>Six weeks after discharge, cranial neuropathies and headaches had
completely resolved. The patient was transitioned to oral ciprofloxacin
for an additional three months with complete resolution of infection and
normalization of CRP. Oral anticoagulation was continued for two months
for continued prophylaxis against venous thrombosis which did not recur.</div><div>DISCUSSION</div><div>SBO is an uncommon condition that can lead to significant morbidity
including cranial neuropathies and intracranial complications. Cranial
nerve (CN) dysfunction can frequently occur with extension to the
jugular foramen (CNs IX, X, and XI), stylomastoid foramen (V), and
petrous apex (V and VI) leading to dysphagia, dysphonia, and facial
weakness <sup>1</sup>. Many pathogens, including<i>Pseudomonas</i> , <i>Streptococcus</i> , and fungal species, can lead
to SBO <sup>1</sup>. A leading cause of SBO remains malignant
otitis externa (MOE) with a <i>Pseudomonas</i> infection occurring in
&gt; 90% of cases, but SBO can also occur from odontogenic,
otogenic, sinogenic, and mastoiditis infections <sup>4</sup>. The
pathogenesis of SBO remains unclear, however, cerumen pH alternations
and impaired immune response and vascular perfusion may provide the
necessary environment for SBO as evidenced by most patients being
diabetic, elderly, or immunocompromised.</div><div>Clinically, SBO may demonstrate signs of overt infection including
fever, leukocytosis, or elevated inflammatory markers. Imaging studies,
commonly utilized for early diagnosis for localization and extent of
infection, are often non-specific but may demonstrate soft tissue
infiltration and bony erosion of the skull base. Compared to CT, MRI has
been shown to have better sensitivity for characterizing disease
infiltrate <sup>5</sup>. SBO can frequently be misdiagnosed for
malignancy which makes biopsy with histopathology necessary. However,
depending on the extension and localization of the infection, obtaining
a biopsy may be difficult.</div><div>Treatment for bacterial SBO involves an extended course of
culture-directed intravenous antibiotics for a minimum of six weeks to
achieve complete resolution <sup>3</sup>. Surgical intervention
for debridement of infected tissue may be beneficial for source control
but can lead to unnecessary morbidity. If left untreated, SBO leads to
significant mortality with the development of meningitis, intracranial
abscess, and venous sinus thrombosis. Overall, the long-term prognosis
of SBO was reported to be 90.5% within 18 months with 31% developing
neurologic sequelae, though certain medical conditions such as diabetes
have demonstrated worse prognosis <sup>1</sup>.</div><div>For the patient in the present case, aside from advanced age, there were
no known risk factors for SBO as hemoglobin A1c was normal, and human
immunodeficiency virus (HIV) testing returned negative. It was
hypothesized the SBO infection was secondary to MOE that may have been a
result of odontogenic seeding with subsequent extension to the skull
base. Nonetheless, <i>Pseudomonas</i> is an uncommon odontogenic
infiltrate making it an unlikely presentation. The case underlines the
importance of recognizing SBO versus similarly presenting malignancy
especially in patients lacking traditional risk factors for prompt
culture-directed antibiotic treatment leading to a favorable outcome.</div><div>CONCLUSION</div><div>SBO mimics the presentation of various conditions, notably skull base
malignancies. For optimal prognosis, prompt diagnosis with core biopsy
for culture and pathology may be necessary that informs antibiotic
selection. Although patients with diabetes or that are immunocompromised
are more susceptible to SBO, not all patients have these risk factors.</div><div>REFERENCES</div><div>1. Khan MA, Quadri SAQ, Kazmi AS, et al. A Comprehensive Review of Skull
Base Osteomyelitis: Diagnostic and Therapeutic Challenges among Various
Presentations. <i>Asian J Neurosurg</i> . 2018;13(4):959-970.
doi:10.4103/ajns.AJNS_90_17</div><div>2. Adams A, Offiah C. Central skull base osteomyelitis as a complication
of necrotizing otitis externa: Imaging findings, complications, and
challenges of diagnosis. <i>Clin Radiol</i> . 2012;67(10):e7-e16.
doi:10.1016/j.crad.2012.02.004</div><div>3. Sokołowski J, Lachowska M, Karchier E, Bartoszewicz R, Niemczyk K.
Skull base osteomyelitis: factors implicating clinical outcome.<i>Acta Neurol Belg</i> . 2019;119(3):431-437.
doi:10.1007/s13760-019-01110-w</div><div>4. Rubin Grandis J, Branstetter BF, Yu VL. The changing face of
malignant (necrotising) external otitis: clinical, radiological, and
anatomic correlations. <i>Lancet Infect Dis</i> . 2004;4(1):34-39.
doi:10.1016/s1473-3099(03)00858-2</div><div>5. Seabold JE, Simonson TM, Weber PC, et al. Cranial osteomyelitis:
diagnosis and follow-up with In-111 white blood cell and Tc-99m
methylene diphosphonate bone SPECT, CT, and MR imaging.<i>Radiology</i> . 1995;196(3):779-788.
doi:10.1148/radiology.196.3.7644643</div><div>Figure 1: Axial computed tomography (A) and T1 Dixon magnetic resonance
imaging (B) demonstrating right central skull base bone erosion
(asterisk) with infiltrating soft tissue mass (arrows).</div><div>Figure 2: Temporal bone axial computed tomography showing right tympanic
membrane (arrows) thickened with narrowed external auditory canal (A)
compared to the normal left tympanic membrane and external auditory
canal (B).</div>