A 13-year-old boy with a pertinent medical history of only allergic rhinitis was hospitalized for septic shock with fever of unknown origin. He had gone diving 10 days prior to admission (PTA). Six-day PTA, he had a fever (38 C) followed by headache, nausea, and vomiting but no diarrhea. Pertinent serologic examination at another hospital revealed white blood cells (WBCs) 10,170/muL, segments 92.6%, and C-reactive protein (CRP) 28.67 mg/dL. The chest radiograph and urinalysis showed no abnormalities. The family refused a lumbar puncture. Intravenous (IV) penicillin was given and the fever gradually subsided. Four-day PTA, right neck pain occurred without a history of trauma or any particular findings in the aforementioned area. One-day PTA, the fever rose to 39 C; right neck pain progressed and he became drowsy. Upon admission, his body temperature was 36.9 C, pulse rate 96/min, respiratory rate 18/min, and blood pressure 70/30 mmHg. Physical examination showed no abnormalities except tenderness on the right side of the neck level II of the submandibular angle without nuchal rigidity, cervical lymphadenopathy, wound, or skin discoloration. Dopamine was given for his shock status on admission. Laboratory data were WBC - 7510/muL, bands - 49%, segments - 32%; platelets - 13,000/muL; CRP - 31.21 mg/dL; slightly elevated fibrinogen/D-dimer; and a normal prothrombin time/activated partial thromboplastin time (PT/aPTT). Fiberscopic examination revealed no evidence of deep neck infection. Under suspicion of atypical infection, IV penicillin and levofloxacin were started and his clinical condition improved. Dopamine was discontinued on the 2nd hospital day (HD), and his fever subsided on the 5th HD. However, right neck pain persisted accompanied by right peripheral facial palsy and ptosis but no visual impairment. Tests for serum Lyme antibody IgG and IgM were normal. Brain magnetic resonance imaging (MRI) on the 6th HD showed a right sphenoid sinus mucocele with a right cavernous sinus and internal jugular vein thrombosis [Figure 1]. Endoscopic incision/drainage was performed. Pathology revealed chronic sphenoiditis. Blood cultures grew Peptostreptococcus; anaerobic pus cultures grew Prevotella loescheii, both sensitive to penicillin. Pus acid-fast stain and tuberculosis cultures were negative. After completing a 4-week course of penicillin and ceftriaxone (levofloxacin was shifted to ceftriaxone due to elevating liver enzymes), he was discharged with full recovery of cranial nerve palsy and no neck pain.