[(18) F]-Fluorodeoxy-d-glucose uptake-positive seborrhoeic keratosis on positron emission tomography may result from high expression of glucose transporter

Irritated seborrhoeic keratosis masquerading as malignancy on 18F-fluorodeoxyglucose positron emission tomography-computed tomography

Seborrhoeic keratosis is a common benign skin tumor and can have a variable presentation. Irritated seborrhoeic keratosis can clinically mimic cutaneous malignancy and often warrant biopsy. ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography-computed tomography (PET-CT) can give false-positive results in many cutaneous pathologies. We present an interesting case of irritated seborrhoeic keratosis masquerading as skin cancer, clinically as well as on¹⁸F-FDG PET-CT.

FDG-Avid Keloid on PET/CT Imaging

Keloid is a benign fibroproliferative growths resulting from an overexuberant healing response. A 51-year-old man with a 20-year history of keloid formation presented with a 1-year history of unexplained progressive weakness of both lower limbs. He was clinically suspected of having paraneoplastic neurologic syndrome. FDG PET/CT was performed to exclude underlying malignancy. FDG PET/CT revealed a giant FDG-avid keloid in the anterior chest wall without any other abnormal FDG uptake in the body. We emphasize that a benign FDG-avid keloid should be considered in the differential diagnosis of FDG-avid cutaneous lesions on PET/CT.

Blastic Plasmacytoid Dendritic Cell Neoplasm Evaluated by FDG PET/CT

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematological malignancy. A 34-year-old man with a biopsy-proven BPDCN underwent FDG PET/CT for staging. FDG PET/CT revealed multiple mild FDG-avid cutaneous lesions on the chest and back, involvement of left inguinal lymph node, and a markedly increased FDG-avid subcutaneous mass in the left lower leg.

[Increased glucose uptake by seborrheic keratosis on PET scan]

BACKGROUND

Positron emission tomography (PET) is an examination based upon the uptake of a radioactive tracer by hypermetabolic cells. It is primarily used in tandem with tomodensitometry (PET-TDM) for cancer staging because of its high sensitivity and specificity for the detection of metastases. However, unusually high uptake may occur with benign tumours, including skin tumours. Herein, we report an extremely rare case of pathological uptake levels resulting from seborrhoeic keratosis.

PATIENTS AND METHODS

A 55-year-old male patient with oesophageal squamous-cell carcinoma was referred to us following the discovery of an area of high marker uptake following PET-TDM and corresponding to a pigmented skin lesion. No other areas of suspect high uptake were seen. The lesion was surgically excised and histological examination indicated seborrhoeic keratosis. The histological appearance was that of standard seborrhoeic keratosis without any notable mitotic activity.

DISCUSSION

PET-TDM is an examination that enables diagnosis of malignancy. However, rare cases have been described of increased marker uptake by benign cutaneous tumours such as histiocytofibroma, pilomatricoma and condyloma. To date, there have only been only very few cases of increased uptake due to seborrhoeic keratosis.

CONCLUSION

This extremely unusual case of increased glucose uptake in PET-TDM due to seborrhoeic keratosis confirms that the hypermetabolic activity detected by this examination is not necessarily synonymous with malignancy and that confirmation by clinical and histological findings is essential. The reasons for increased metabolic activity within such benign tumours are not known.