Infected/Inflamed Sebaceous Cyst or Carbuncle

Sebaceous cysts are well-defined lesions commonly seen within the subcutaneous fat, abutting the overlying skin. They are typically hypodense and non-avid.

Occasionally, they can become infected/inflamed and appear intensely FDG-avid.  In such cases, they cannot be readily distinguished from primary skin lesions or metastatic disease (especially metastases from melanoma).

If purely an incidental finding in a non-melanoma patient (especially if non-avid on a prior exam), we describe the finding and report that it “typically represents an inflamed/infected sebaceous cyst or carbuncle. Please correlate with physical examination.”

In a melanoma patient, we are more cautious to raise the possibility of metastatic disease: “While this may represent an inflamed/infected sebaceous cyst or carbuncle, a metastatic lesion should be excluded in a patient with a history of melanoma. Correlation with physical examination is strongly recommended.”