18F-FDG Tumor Imaging Clinical Applications

            The most frequent and useful indications for FDG PET imaging are listed below. This technique may especially be employed to differentiate malignant from benign lesions, if the level of uptake is considered. Normally malignant processes pick up glucose intensively and corresponding SUV are clearly elevated in the majority. This may help in the diagnosis of a primary tumor. In cases where this tumor is unknown FDG PET can detect up to 30% to 40 % of these primaries.

Head and Neck:        Head and Neck Cancers     Pituitary Adenoma   Thyroid Follicular Carcinoma

Thorax:                      Lung Cancer       Breast Cancer                                  

Gastrointestinal:     Esophageal Cancer     Pancreatic Carcinoma    Colorectal Cancer    Gastric Carcinoma

Hematologic:            Lymphomas       Multiple Myeloma

Gynecologic:            Endometrial Cancer

 Skin:                        Melanoma

            Other indications comprise staging, and therapy monitoring. This is particularly valuable because PET can depict cell metabolism in a direct way and characterize tumoral viability. Normally, sensitivity is over 90% in the detection of secondary extension of the malignancies commented above.

            Nonetheless, it must be known that in some metastatic conditions FDG PET value may be limited. It is the case of peritoneal carcinomatosis. Dromain C et al. reported 30 patients with suspected peritoneal carcinomatosis of gastrointestinal tract. All patients had been operated on the primary tumor. Colon 50%, Appendix 33%, Rectum 10%, Stomach 3.5%, Small Bowel 3.5%. The sensitivity for the diagnosis of peritoneal carcinomatosis was 57% for PET-CT (3). This is explained in most cases due the small size of the lesions and the diffuse rather than focal involvement.

            False positives were as follows: pneumoniae, tuberculosis, sarcoidosis, cryptococcosis, thrombosis, bronchitis, costochondritis, radiation pneumonitis, artifact due to respiratory movements, catheters, thyroid and adrenal adenomas, osteophytes, fractures, abscess, foreign body, surgical wounds, ostomies, prosthesis, degenerative joint diseases, osteomyelitis, amyloidosis, pancreatitis, myositis, gastritis, colitis, herpes zoster. FDG should be injected 4-6 h after insulin administration otherwise it will concentrate markedly in the muscles. Brown fat reinforces its uptake up to 50% in late images (4). Consider also silicosis. Likewise, brown fat FDG uptake has to ruled out as cause of false positive study (5).
 

            Patients on Chemotherapy and bone marrow agents, may present with diffuse marrow homogeneous uptake, which later on becomes normal.

References:

1  Simo M. Utilidad de la Tomografia PET en cancer de mama, p: 535-541 and Setoain X. PET en los linfomas, p: 543-547. En Medicina Nuclear Aplicaciones Clínicas. Eds: I. Carrio - P. González. Editorial Masson, Barcelona España, 2003.

2  Rohren EM, Turkington TG, Coleman RE. Clinical applications of PET in oncology. Radiology. 2004 May;231(2):305-32.

3  Dromain C, Leboulleux S, Auperin A, Goere D, Malka D, Lumbroso J, Schumberger M, Sigal R, Elias D. Staging of peritoneal carcinomatosis: enhanced CT vs. PET/CT.Abdom Imaging. 2008 Jan-Feb;33(1):87-93.

4  Del Rocío Estrada-Sánchez G, Altamirano-Ley J, Ochoa-Carrillo FJ.Normal variants and frequent pitfalls with (18)FDG PET/CT study.Cir Cir. 2007 Nov-Dec;75(6):491-7.


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