Benign Bone Lesions

Although malignant bone tumors generally have greater FDG uptake than benign lesions, there are simply too many hypermetabolic benign bone lesions to make PET/CT very useful as an indicator of malignancy or benignity.

False Positives: Many benign lesion often demonstrate moderate to intense metabolic activity, including fibrous dysplasia, non-ossifying fibroma, giant cell tumor, aneurysmal bone cyst, Paget’s disease, enchondroma, osteomyelitis, bone infarct and chondroblastoma.

False Negatives:  Several malignant bone lesions often demonstrate little or no activity, including low-grade chondrosarcoma, plasmacytoma and myxoid tumors.

Attempting to use PET/CT to distinguish malignant from benign lesions is simply unreliable.

Vertebral Body Hemangioma:  

Vertebral body hemangiomas are regularly seen on PET/CT scans and are non-avid.

On CT images, they classically demonstrate a “striated” appearance on sagittal images and a “stippled” appearance on axial images.

While the CT appearance alone is usually diagnostic for hemangiomas, there are cases when it is reassuring to confirm the diagnosis by an absence of metabolic activity on the PET portion of the exam (particularly for those cases where a prior MRI has been equivocal, suggesting the possibility of an “atypical hemangioma”). 

Schmorl’s Node:

A Schmorl’s node is a focal herniation of disc material into a vertebral body.  It appears as a rounded lucency in the vertebral body, contiguous with its endplate. The lucency often demonstrates surrounding sclerosis.

While typically non-avid, Schmorl’s nodes can be FDG-avid, occasionally demonstrating even intense metabolic activity. MRI evaluation may occasionally be required to distinguish a hypermetabolic Schmorl’s node from a lytic metastasis.

Primary Malignant Bone Tumors: 

The role of PET/CT for patients with primary malignant bone tumors is addressed in detail,  here.