Pilomatricoma of the thoracic dorsal skin: A benign tumor mimicking soft tissue malignancy on 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging

Introduction: Objectives

1. To evaluate the clinicopathologic features of pilomatricoma.

2. To highlight the indications of positron emission tomography in pilomatricoma.

3. To evaluate the characteristics of pilomatricoma in magnetic resonance imaging.

Background

Pilomatricoma is a benign skin tumor originating from the hair matrix cells in the skin dermis, common in the head and neck region and relatively rare in other areas, such as the trunk. The clinical diagnosis of pilomatricoma is difficult. On observation under a pathological microscope, the tumor cells were seen to be chiefly composed of basaloid and ghost cells, with varying numbers of transitional cells, and calcification was present in cell masses. In recent years, positron emission tomography/magnetic resonance imaging (PET/MRI) has been used for the partial staging and examination of soft tissue malignancies; however, there have only been a few reports on the findings of pilomatricoma.

Methods: This study reports a case of a large cutaneous tumor of the trunk, which was misdiagnosed as a malignant soft tissue tumor before surgery. A 14-year-old girl was admitted for PET/MRI because of a gradually enlarging skin mass present on the trunk, which was clinically suspected to be a malignant tumor.

Results: The 5-cm marked fluorodeoxyglucose (FDG) uptake skin mass (SUVmax13) was present on the thoracic dorsal spine region. The mass showed isointensity on T1-weighted imaging, heterogeneous hypointensity on T2-weighted imaging (T2WI), hyperintensity on diffusion-weighted imaging, and remarkable enhancement of the target ring on enhanced scans. The benign histological test results suggested that FDG uptake was not tumor-specific, false-positive uptake of FDG may have also occurred under inflammatory conditions, and the presence of a foreign body giant cells in a pilomatricoma suggested chronic inflammation. In addition, hypointensity on T2WI may indicate the calcification components of the tumor, and the enhancement of the target ring may be an MRI enhancement characteristic of pilomatricoma.

Conclusions: In conclusion, pilomatricoma should be considered an uncommon differential diagnosis of FDG-avid cutaneous lesions, and PET/MRI may provide more information for the accurate preoperative diagnosis of pilomatricoma.

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