18F-FDG PET CT

18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET CT) is an established method for the staging of carcinomas. The bone scan is an old method to detect skeletal metastasis. Both the modalities are usually normal in vertebral hemangiomas. However, there have been case reports of increased osteoblastic activity on bone scan; with normal metabolic activity on PET scan in vertebral hemangiomas and vice versa.

Thus, in a suspected vertebral hemangioma it is important to recognize that either of these tests may be falsely positive. Discordance between FDG and bone scan in presence of radiologic (CT or MRI) features of hemangioma; may prevent an unnecessary invasive procedure. A 51 years old man with poorly differentiated tonsillar carcinoma had well defined enhancing hypodense mass in left tonsillar fossa measuring 36×29×58 MMS with neck nodes on CT scan.

Biopsy from neck nodes

Therefore Biopsy from neck nodes showed metastasis from squamous cell carcinoma. The patient was treated with radiotherapy using Intensity-Modulated Radiation Therapy (IMRT) technique to administer 7000 cGy in 35 fractions. Concurrent weekly Cisplatin was administered intravenously in the dose of 40 mg/square meter body surface area. Post-treatment PET/CT was performed at 1 hour after intravenous administration of 6.8 mCi 18F-FDG on 6 hours fasting state.

Images are acquired using 16 slice time of flight biograph horizon scanner from Siemens. Left tonsillar fossa-base of the tongue-lateral oropharyngeal wall was free of FDG avid lesions or cervical nodes suggesting the response to treatment. Axial CT images showed ‘polka dot’ appearance in 12ththoracic vertebra suggestive of hemangioma. However, the lesion showed intense FDG uptake with SUV max of 13.44  raising suspicion of metastasis.

The patient was asymptomatic. In view of this, a whole body bone scan performed on another day, 3 hours after intravenous injection of 20 mCi of Tc-99m-MDP (Methylene Diphosphonate) using a single head E-cam gamma camera (Siemens) equipped with low energy high-resolution collimator. The images did not reveal any osteoblastic lesion. Skeletal hemangiomas are asymptomatic and usually incidentally detected on CT or MRI. They are of four types of hemangioma: capillary, cavernous, arteriovenous and venous.

The Hamartomatous Proliferation of Vascular Tissue

They commonly saw in vertebrae and ribs. Microscopically there is the hamartomatous proliferation of vascular tissue. They are slow growing and cause displacement of normal bone that may appear as a lytic lesion on radiograph causing corduroy cloth appearance and ‘polka dot appearance’ on CT scan due to thickened trabeculae. MRI shows high signal intensity due to the presence of fat on T1 weighted images (T1W). T2W sequences show a higher signal than T1W due to water content. After contrast injection T1W shows enhancement due to high vascularity.

Bone scan shows normal osteoblastic activity within these lesions. Rarely, these lesions may be either cold or hot on bone scan. FDG PET scan is usually normal in such cases. However, in the present case;l FDG PET showed hot vertebra and bone scan was normal. Thus, if there is hot vertebra on FDG scan and the normal bone scan of the vertebra along with characteristic signs of hemangioma on CT or MRI, the biopsy is avoidable. There is a case report of ‘hot’ vertebral hemangioma.

18F-FDG PET CT

18F-FDG PET CT reported localizing in malignant as well as benign skeletal lesions. So Pigmented villonodular synovitis, sarcoidosis, neurofibroma, schwannoma, giant cell tumor, osteoid osteoma, histiocytosis X, chondroblastoma, enchondroma, brown tumor, and non-ossifying fibroma are the benign lesions that may show FDG uptake. Mesenchymal tumors associated with tumor-induced osteomalacia (TIO) have been divided into 1) phosphaturic mesenchymal tumor; mixed connective tissue type (PMTMCT); 2) osteoblastoma-like tumors; 3) ossifying fibrous-like tumors; and 4) nonossifying fibrous-like tumors.

 18F-FDG PET CT, Gallium-68 Somatostatin receptor PET CT  reported to detect mesenchymal tumors in TIO. Usually, a hypermetabolic lesion on FDG PET scan in presence of normal bone scan and radiology invariably implies metastasis. The case had the hot 12th thoracic vertebral body on FDG PET CT scan. There were two additional pointers towards hemangioma in this case.

CT scan showed typical polka dot appearance and bone scan was normal suggesting a benign etiology. Clinically the patients asymptomatic and a biopsy avoided. Thus a discordance between FDG PET CT and Bone scan in presence of radiologic features of hemangioma is probably an indication for conservation in an asymptomatic patient.