FDG PET positive benign peripheral Schwannoma

Case contributed by Dr. Chris O'Donnell

Presentation

PH of malignant melanoma. Recent PET scan shows an avid mass in left popliteal fossa. For further investigation prior to excision. Histology - benign Schwannoma

Patient Data

Age: 60
Gender: Male

PET scan

Nuclear medicine

Rounded mass in the left popliteal fossa showing subtle but definite uptake of FDG

Large well-defined mass in the politeal fossa intimately related to the common peroneal nerve (arrow) shwoing an internal "spoke wheel" appearance and patchy enhancement following Gd contrast.  Edema in surrounding soft tissues.

Well-defined, lobulated mass with internal "microcystic" appearance and internal blood flow on color Doppler

Case Discussion

Schwannomas or neurilemomas are reasonly common benign nerve sheath tumors that can affect most if not all peripheral nerves.  They are in general FDG avid and should be included in the differential of mass lesions detected on PET.  There is unfortunately no correlation between avidity and aggressiveness i.e. the presence of marked FDG uptake (high SUV > 6) does not necessarily indicate a malignant nerve cell tumor.

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