Anshu R. Sharma

Therapeutic Response to Radiofrequency Ablation of Neoplastic Lesions: FDG PET/CT Findings

Ablation of neoplastic lesions by using radiofrequency energy is gaining popularity in clinical practice because of the minimally invasive nature of radiofrequency ablation (RFA). Primary and secondary tumors of the liver and lung are treated with RFA when surgery is precluded because of comorbidity. Benign bone tumors are also treated with RFA to relieve pain and prevent further tumor growth. Differentiation between postablation tissue changes and residual disease is difficult with morphologic imaging modalities such as ultrasonography, computed tomography (CT), and magnetic resonance (MR) imaging, thus limiting the use of these modalities to detection of residual disease early after RFA. Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is a functional imaging modality that can be used to study the effects and efficacy of RFA. Lesions that show increased FDG uptake at PET become completely photopenic immediately after RFA, a finding that is suggestive of the completeness of ablation. Focal areas of increased FDG uptake within the ablated zone are suggestive of residual disease. Reactive tissue changes such as inflammation are depicted in the periphery of the ablated lesion and show a uniform low-grade FDG uptake, which can be differentiated from the focal, nodular intense uptake in areas of residual disease. Use of combined FDG PET/CT to detect residual disease early after RFA allows ablation to be repeated, if necessary, to obtain the maximum therapeutic benefit. Note that FDG uptake in the complications sometimes associated with RFA can be a cause of potential false-positive PET results.

Integrated PET/CT in evaluating sarcomatous transformation in osteochondromas.

Aim: To study the role of PET-CT in evaluating sarcomatous transformation in osteochondromas. Materials and Methods: This was a retrospective analysis of a prospective data base of 12 patients from 2005 to 2007 with a clinical diagnosis of an osteocartilaginous lesion who were referred for a FDG PET-CT study to evaluate for possible malignant transformation. Imaging was performed on a GE Discovery ST PET-CT system after intravenous injection of 370 MBq (10 mCi) of F-18 FDG. Results: Seven patients with histopathological evidence of a sarcomatous transformation to grade II chondrosarcoma showed moderate to high FDG uptake (SUV 3.3–6.9), whereas 1 patient with a dedifferentiated chondrosarcoma showed a focus of very intense uptake (SUV 11.4). Four patients with histopathological and/or clinical or follow-up diagnosis of a benign osteocartilaginous lesion showed low grade FDG uptake (SUV 0.8–1.3). FDG uptake was also noted in an asymptomatic osteochondroma which on histopathology revealed a grade II chondrosarcoma. Conclusions: Whole body FDG PET-CT is an important adjunct to conventional morphologic imaging in evaluating suspected malignant transformation in osteochondromas. Increased glucose metabolism can help diagnose sarcomatous transformation at the suspected sites as well as detect early malignant change at clinically unsuspected sites. Moreover, its ability to detect a focus of dedifferentiation can be useful for prognostication and to plan adjuvant treatment. A small cohort limits statistically sound conclusions to be drawn from this study, however further prospective trials based on these findings can help explore the potential application of FDG PET-CT in this clinical condition.

Pulmonary artery and femoral vein tumour thromboembolism in a patient with osteogenic sarcoma demonstrated by FDG PET/CT

FDG PET/CT is frequently used in staging and restaging of sarcomas. A 35-year-old man who had undergone an abovethe-knee amputation for an osteosarcoma of the right tibia presented with localized swelling and progressive dyspnoea whileonfollowup.TheMIPimage(a) from a restaging PET/ CT study revealed linear tracer uptake (arrow) in the right thigh along with hypermetabolic branching foci in the chest. A contrast-enhanced CT scan of the chest (b )r evealed nonocclusive branching intraluminal filling defects (arrow) in both pulmonary arteries. The fusion PET/CT image (c) showed moderate to high-grade FDG uptake (SUV 7.8) corresponding to the linear filling defects in the pulmonary arteries (arrow) suggesting the diagnosis of pulmonary tumour emboli. The linear uptake in the thigh was confirmed by ultrasonography as a deep femoral vein thrombus. Metastases and infection are frequent causes of respiratory symptoms in patients with osteosarcoma. Rarely the tumour cells can permeate the major veins and give rise to pulmonary tumour emboli [1]. The diagnosis is then unsuspected as the symptoms are nonspecific [2]. Pulmonary artery filling defects showing significant tracer uptake on fusion images in such a patient serve as indirect evidence for tumour embolism, proof of which is obtained from embolectomy [3] or autopsy [4] specimens. We demonstrate the characteristic FDG PET/CT findings of pulmonary artery and femoral vein tumour thrombi, a rare consequence of osteosarcoma, not previously described on FDG PET/CT imaging.

Pulmonary hydatid cyst detected on FDG PET-CT.

A 40-year-old man on follow-up for treated tongue cancer was evaluated with a chest radiograph for cough of recent onset. The radiograph revealed a lung mass which was diagnosed as hydatid cyst after surgical resection. Tapeworms of the genus Echinococcus cause hydatid disease in humans, which most commonly involves the liver. Pulmonary hydatid cysts may, however, be seen in isolation. These have varied imaging appearances and can often be mistaken for a lung mass or masses of more sinister origins. We describe the positron emission tomography-computed tomography appearance of a lung hydatid cyst.

Long-segment intramedullary spinal dermoid

A 30-year-old man presented with a fairly large intramedullary mass lesion involving virtually the entire spinal cord. It was hyperintense on both T1W and T2W sequences, with signal suppression on fat-saturation images. Subsequent noncontrast CT scan of the spine confirmed the presence of fat and calcification within the lesion, thus leading to the diagnosis of an intramedullary dermoid.

PET/CT: Current status in India.

PET/CT is a new modality with integration of PET and CT systems. In India, since December 2004 there has been a steady increase in the number of imaging systems. From stand-alone PET/CT systems with on-site cyclotrons, mostly in the government sector, the modality has matured to such an extent that, today, the majority of the PET/CT scanners and cyclotrons are in the private setup; also, scanners situated in different locations (and even different cities) share the isotope produced from one cyclotron. This shows how much this field has developed and reflects the confidence of the end users. The current status of PET/CT in India is indeed healthy and heartening and the future certainly looks promising.

Bone infarct-associated sarcoma detected on FDG PET/CT.

Secondary sarcomas arising on the background of a bone infarct are extremely uncommon. Based on the knowledge of classic imaging patterns, however, lesions like bone infarcts can be recognized during positron emission tomography/computed tomography studies, which are now being performed increasingly in cancer patients. We demonstrate the detection of this rare entity on positron emission tomography/computed tomography and its correlation on magnetic resonance imaging in a 56-year-old man with asymptomatic multifocal osteonecrosis secondary to steroid treatment for polymyositis.

Case report: Epidermoid cyst misdiagnosed as a loculated pericardial effusion.

A 25-year old man presented with a mediastinal lesion which was initially diagnosed as a loculated pericardial collection on echocardiography. Subsequent imaging showed it to be a cystic mediastinal mass, and following surgery and histopathology, it turned out to be an epidermoid cyst.

Unusual lower limb skeletal metastases from carcinoma of the cervix: detection by F-18 FDG PET/CT.

Osseous metastases from carcinoma of the cervix are often associated with locoregional and nodal recurrence, and bear an adverse correlation with survival. The lumbar spine is the commonest site and metastases to the distal appendicular and sacral bones are an infrequent finding. Positron emission tomography/computed tomography (PET/CT) using fluorodeoxyglucose as tracer (FDG) is being increasingly used in staging and follow-up of patients treated for carcinoma of the cervix. We report rare osseous sites of metastatic recurrence in the tibia, patella, and the intermediate cuneiform detected on FDG PET/CT in a patient treated for cervical cancer, findings hitherto undescribed.

FDG PET-CT findings in epiploic appendagitis.

Abstract:Positron emission tomography (PET) using flourodeoxyglucose (FDG) is routinely used for initial staging and restaging of colorectal cancers. However FDG PET studies can suffer from false-positive tracer uptake due to a variety of physiological and inflammatory conditions arising in the abdo