Infected Frontal Sinus Mucocele Mimicking a Cutaneous Abscess.

Frontal sinus mucoceles are benign expansile lesions that may progressively erode the surrounding bone and extend toward the orbit or intracranial compartment. When expansion occurs anteriorly, however, they may present as an apparently superficial forehead swelling and be mistaken for a cutaneous abscess. A 77-year-old woman with chronic sinusitis developed recurrent left paramedian frontal swelling over several months, with only transient improvement following antibiotic treatment. The lesion was initially interpreted as a cutaneous abscess and incised in an outpatient setting. Clear, nonpurulent fluid was obtained instead of pus. Two days later, she presented with persistent frontal inflammation and newly developed left periorbital cellulitis. Despite the extent of the disease, she remained afebrile and had no headache, neurological symptoms, diplopia, or visual impairment. CT and MRI demonstrated a left frontal sinus mucocele with erosion of both the anterior and posterior frontal sinus tables, in close proximity to the superomedial orbit and dura mater. After control of the acute inflammatory process, the mucocele was treated with endoscopic endonasal marsupialization through a Draf IIc frontal sinusotomy. Complete clinical resolution was achieved, with no documented recurrence during one year of follow-up. This case illustrates an important diagnostic pitfall: the superficial appearance of a frontal swelling may conceal extensive underlying sinus disease and bony erosion. Recurrent paramedian frontal swelling, transient responses to antibiotics, clear rather than purulent drainage, or associated periorbital inflammation should prompt CT or MRI before any further incision.