DOI: 10.1148/radiol.2402040441
(Radiology 2006;240:611-612.)
© RSNA, 2006
The Straight Line Sign1
Pramod Gupta, MD
1 From the Division of Nuclear Medicine, New York University Medical Center, 560 First Ave, New York, NY 10016. Received March 5, 2004; revision requested May 19; revision received June 3; accepted June 15.
Address correspondence to the author (e-mail: guptap01{at}popmail.med.nyu.edu).
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APPEARANCE
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The straight line sign demarcates the boundary between increased diffuse activity in the peritoneum and lower, normal levels of activity in the retroperitoneum on sagittal positron emission tomography (PET) images with fluorine 18 fluorodeoxyglucose (FDG) (Figure).
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Parasagittal FDG PET scan in a 56-year-old female patient with diffuse peritoneal carcinomatosis who underwent resection of an ovarian tumor. Image shows a line (arrows) demarcating diffuse increased FDG uptake in the peritoneum from much lower normal activity in the retroperitoneum. Uptake in the renal parenchyma (arrowhead) demarcates the superior location of the retroperitoneum.
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EXPLANATION
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The appearance of the sign is due to diffuse hypermetabolism in metastases spread uniformly throughout the abdominal and pelvic peritoneum combined with much lower levels of metabolic activity in the normal retroperitoneum. This is characteristic of diffuse peritoneal carcinomatosis (1).
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DISCUSSION
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The peritoneum is the site of metastasis from several primary malignancies, principally colorectal, ovarian, gastric, and pancreatic carcinomas and occasionally lung and breast carcinomas. The presence of peritoneal disease alters tumor staging, with implications for primary treatment and patient outcome. This is particularly true for colorectal and ovarian carcinomas, in which peritoneal involvement has the greatest independent prognostic significance (2,3). Early diagnosis of peritoneal involvement is important because low-volume disease may be treatable with cytoreductive therapy before surgery. However, peritoneal disease may remain occult for some time because imaging modalities have variable sensitivity in detection of tumor deposits, and the effectiveness of laparoscopic techniques may be limited by sampling error. PET performed with FDG is a powerful, noninvasive functional imaging tool that capitalizes on the increased rates of glucose metabolism of malignant cells.
In patients with colorectal cancer, Tanaka et al (4) demonstrated the increased sensitivity of FDG PET (88%) over computed tomography (CT) (33%), which is currently the preoperative standard for evaluation of peritoneal carcinomatosis. In comparison to contemporaneous peritoneal biopsy and ascitic aspiration, FDG PET and CT showed lower sensitivities for peritoneal carcinomatosis (57% and 43%, respectively). Combining PET and CT findings increased sensitivity further than could have been achieved with either modality alone (78%), while also maintaining a high positive predictive value (95%).
Two distinct and abnormal patterns of FDG uptake at PET, focal and uniform, correspond to nodular and diffuse peritoneal disease, respectively (5).
The straight line sign has been described as an early indicator of diffuse peritoneal carcinomatosis on PET images and thus can help with the early diagnosis of diffuse peritoneal disease (1).
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ACKNOWLEDGMENTS
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I am extremely thankful to Elissa Kramer, MD, for her input in preparation of the manuscript.
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FOOTNOTES
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Author stated no financial relationship to disclose.
| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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- Lin EC. "Straight line" sign of diffuse peritoneal carcinomatosis on sagittal FDG positron emission tomographic images. Clin Nucl Med 2002;27:735–736.[CrossRef][Medline]
- Shepherd NA, Baxter KJ, Love SB. The prognostic importance of peritoneal involvement in colonic cancer: a prospective evaluation. Gastroenterology 1997;112:1096–1102.[CrossRef][Medline]
- Simojoki M, Santala M, Vuopala S, Kauppila A. The prognostic value of peritoneal cytology in ovarian cancer. Eur J Gynaecol Oncol 1999;20:357–360.[Medline]
- Tanaka T, Kawai Y, Kanai M, Taki Y, Nakamoto Y, Takabayashi A. Usefulness of FDG-positron emission tomography in diagnostic peritoneal recurrence of colorectal cancer. Am J Surg 2002;184:433–436.[CrossRef][Medline]
- Turlakow A, Yeung HW, Salmon AS, Macapinlac HA, Larson SM. Peritoneal carcinomatosis: role of (18)F-FDG PET. J Nucl Med 2003;44:1407–1412.[Abstract/Free Full Text]
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