Haluk Alibazoglu

Hematopoietic cytokine-mediated FDG uptake simulates the appearance of diffuse metastatic disease on whole-body PET imaging

FDG-PET is increasingly being used to assess malignant tumors. However, leukocyte colony-stimulating factors (CSFs), which promote the expansion of hematopoietic bone marrow, have also been demonstrated to cause increased bone-marrow FDG uptake. Three hundred FDG-PET studies conducted over a 1-year period were reviewed for diffuse bone-marrow uptake. Elevated bone-marrow uptake on PET was correlated with pathological findings and courses of granulocyte-CSF (G-CSF) therapy. These results demonstrate that G-CSF mediated FDG uptake in bone marrow is often indistinguishable from that caused by disseminated metastatic disease. However, the bone-marrow response to G-CSF decreases rapidly following the last CSF administration. Therefore, FDG-PET in patients receiving G-CSF should be delayed, when possible, until 5 days after the end of G-CSF therapy.

Normal thymic uptake of FDG on PET imaging

Assessment and characterization of the thymus by various imaging methods have been extensively described. The authors report increased uptake of 2-(18)Fluoro-2-deoxy-D-glucose (FDG) in the normal thymus gland of patients between the ages of 2 and 13 years. Most of these patients had PET scans for various oncologic conditions and had no clinical problems referable to the thymus gland. This uptake assumes an important role when evaluating mediastinal uptake in whole-body PET scans in pediatric oncology patients to avoid false-positive interpretation.

Response of Osteosarcoma to Chemotherapy: Evaluation with F-18 FDG-PET Scans

Objective: Positron emission tomography (PET) using fluorine-18-fluoro-2-D-deoxyglucose (FDG) is increasingly being used to evaluate and manage oncology patients. Several reports have documented its utility in diagnosis, staging, response to treatment, and tumor viability assessment. There is, however, a paucity of literature on PET scanning in patients with osteosarcoma. We report results of serial F-18 FDG-PET scans in 16 untreated patients with osteosarcoma who underwent chemotherapy prior to surgical resection of the primary tumor site.Procedure: Changes in tumor fluoro-2-D-deoxyglucose (FDG) uptake were correlated with percent tumor necrosis on histopathology. PET studies were analyzed by visual assessment of tumor uptake of FDG by 3 independent observers, calculating a tumor to normal background activity ratio (TBR) by drawing regions of interest (ROIs) around the tumor and background activity in the contralateral normal limb, and percent change in TBR values between baseline and presurgical study.Results: All patients had positive baseline scans. Baseline TBRs ranged between 2.5-8.7 and visual assessment of intensity of FDG uptake was 2-3 on a scale of 0-3. At histopathologic examination, 8 patients were classified as good responses with more than 90% tumor necrosis and 8 patients as poor responses with less than 90% necrosis. Tumor necrosis was accurately predicted on PET scan in 15/16 patients by visual assessment, 14/15 patients by final TBR value on presurgery scans, and 7/15 patients using percent change of TBR on serial scans.Conclusions: The results of this small series suggest that FDG-PET scanning is fairly accurate in evaluating the response of osteosarcoma to chemotherapy. Visual assessment and TBR are more accurate in predicting tumor necrosis than percent change in TBR on serial scans.

Normal thymic uptake of 2-deoxy-2[F-18]fluoro-D-glucose.

Whole-body 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) positron emission tomography (PET) of a 54-year-old woman with a history of recurrent thyroid follicular cancer and an elevated thyroglobulin level showed significant FDG uptake in the thyroid bed and anterior mediastinum. A previous scan after high-dose I-131 therapy also showed iodine uptake in these regions. Because of a lack of response to iodine therapy, the patient had surgery. Recurrent thyroid cancer was found in the neck, but the mediastinal lesion was shown to consist of normal thymus tissue. In repeated examinations performed after surgery, there was no uptake of FDG or I-131 in the anterior mediastinum. Previous treatment with a high dose of radioiodine may have contributed to visualization of a normal adult thymus with FDG PET.

Injection artifact on FDG PET imaging

Uptake of Tc-99m MDP in lymph nodes due to tracer extravasation at the injection site has been previously reported. We report the uptake of F-18 FDG in axillary lymph nodes due to partial subcutaneous injection of the radiopharmaceutical in the antecubital fossa.

'False-positive' uptake of FDG in a hepatic adenoma

Positron emission tomography using F-18 FDG is becoming a very useful test in the evaluation of many tumors because of its high sensitivity and specificity. However, on rare occasions, it may be difficult to differentiate a neoplasm from a benign lesion. This article describes increased metabolic activity in a hepatic mass found on a routine follow-up CT examination of the abdomen in a 41-year-old woman with a history of bilateral breast carcinoma. Based on an elevated differential uptake ratio of 4.2, the lesion was thought to be consistent with a metastatic tumor. The hepatic mass was removed surgically and proved to be a hepatic adenoma.

Follow-up of sweat gland carcinoma by FDG-PET imaging

Sweat gland carcinoma is a rare malignancy of the skin with a poor prognosis. The principal mode of therapy has been local surgical excision, which may be supplemented by adjuvant chemotherapy and radiotherapy. More than 50% of patients develop either local tumor recurrence or regional lymph node metastases after surgery. The authors report a case of sweat gland carcinoma in which recurrence was detected by F-18 FDG PET imaging. FDG PET imaging can be helpful in early detection of local recurrence.

False-negative FDG PET imaging in a patient with metastatic melanoma and ileal intussusception.

A 34-year-old woman with a history of malignant melanoma had no FDG uptake in a large melanoma deposit in the small bowel on a whole-body scan. However, a large metastatic lesion was identified correctly in the liver.

FDG uptake in gestational sac.

A 39-year-old woman, with a newly diagnosed malignant melanoma of the right calf had negative CT scans of chest, abdomen, and thighs. Two weeks later, a whole body F-18 FDG PET scan showed a focal area of markedly increased metabolic activity in the left side of the pelvis, above and slightly posterior to the urinary bladder. A week later, ultrasound showed a well formed 5-week-old gestational sac in the left side of the uterus. The patient had a 10-year history of birth control pill use and reported she had menstrual bleeding a week before a CT scan.

Fluorine-18 fluorodeoxyglucose uptake in tubovillous adenoma of the colon.

The authors report intense uptake of fluorine-18 fluorodeoxygluclose in benign tubovillous adenoma of the sigmoid colon in a patient with a history of renal cell cancer who was being evaluated for metastatic disease.