“Face mask sign” on Tc-99m methylene diphosphonate bone scan

Abstract

Although bone scan is a sensitive imaging modality, it is nonspecific, and there are multiple potential causes of abnormal isotope uptake that can mimic metastatic disease. A 67-year-old male, a known case of prostate carcinoma, underwent bone scan for skeletal evaluation. His prostate biopsy had revealed adenocarcinoma of the prostate. His serum prostate-specific antigen level was 11.8 ng/ml. The scan showed increased tracer uptake in bilateral maxillary sinuses mimicking shape of the face mask. To characterize the abnormal tracer uptake in the bilateral maxillary sinuses and rule out the metastatic lesion, single-photon emission computed tomography–computed tomography (SPECT-CT) correlation was obtained. The SPECT-CT revealed mucosal thickening obliterating sinus space in the bilateral maxillary sinuses, suggesting the uptake secondary to maxillary sinusitis. On questioning, the patient admitted of having chronic history of pain along the sides of the nose and yellowish nasal mucus discharge. We concluded the uptake to be result of the bilateral maxillary sinusitis. We propose that such uptake pattern can be designated as 'face mask sign' on bone scan.