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EDUCATION EXHIBIT |
1 Department of Radiology, Beth Israel Deaconess Medical Center, Boston, Massachusetts
In the preceding article, Hanbidge et al (1) present a comprehensive review of the spectrum of clinical and US manifestations of diseases of the peritoneum. This timely review summarizes the vast and varied experience of the authors, highlights their learned lessons, and shares with us their wealth of illustrative cases.
In its diagnostic capacity, US continues to play an essential role in identification and characterization of fluid within the peritoneal cavity. A thorough comprehension of the anatomic relationship between the omentum, mesentery, and peritoneum, coupled with an understanding of the preferential pathways that fluid, tumors, or infectious processes may take during their intraperitoneal passage, will certainly strengthen the overall diagnostic usefulness of the US examination and help the examiner formulate a rational and practical differential diagnosis.
The authors describe essential technical requirements for performing the examination. In addition to those described, careful attention must also be focused on optimizing the gain and depth settings, as well as on patient positioning, to fully evaluate as much of the peritoneum and deep pelvic recesses as possible. In regard to additional technical aspects of the examination, the authors state that "a tailored transvaginal examination is mandatory to assess the pelvic peritoneum and cavity in female patients." Many centers do not routinely include a transvaginal component when scanning the abdomen for peritoneal diseases, such as carcinomatosis. However, when appropriate indications do exist, including acute pelvic symptoms, the transvaginal study is extremely sensitive for detection of small quantities of fluid or blood but somewhat less sensitive for detecting more complex pathologic conditions, including drop metastases or extraovarian endometriosis. In the setting of acute pelvic pain, it is also important to include the kidneys in the examination, since small quantities of fluid may traverse the peritoneal cavity to reside within the Morison pouch, providing a subtle clue to the presence of a more complex and remote process.
An expanding clinical use for US has been that of the focused abdominal US examination in the acute trauma setting (2), where a rapid targeted study is commonly performed in many major trauma centers to identify the presence of blood in anticipated locations. The preceding article may be especially helpful to the broader medical fraternity for depicting additional intraperitoneal diseases and causes of fluid.
A few words of caution are necessary before readers consider US as the sole imaging modality for evaluating the peritoneum. CT continues to provide a rapid global evaluation of the entire abdomen and may be used to direct the US examination to specific sites for characterization of fluid or even to facilitate or guide diagnostic aspiration. Also, CT is still more likely to allow identification of abnormalities of the bowel wall or pathologic foci residing in interloop locations.
In addition, US is less likely to allow confident distinction of postoperative fluid collections from complex peritoneal processes, including omental metastases or recurrence of tumor. Although US is very sensitive for detection of small quantities of fluid, it really is quite challenging to accurately quantify the total volume of ascites, given the natural propensity for widespread dissemination of intraperitoneal fluid.
When the quantity of peritoneal fluid is small or when several separate collections are present, we frequently face a clinical dilemma as to which collection is best to aspirate. When imaging patients with spontaneous bacterial peritonitis, many of whom have underlying ascites on the basis of reduced hepatic synthetic function, it is important to realize that infected ascitic fluid may appear entirely anechoic at US; therefore, the presence of infected ascites cannot be reliably excluded with US. However, since US excels at characterizing the nature of fluid, identification of a single pocket of fluid characterized by a more echogenic appearance is more likely to yield a positive aspirate. To characterize the spectrum of US appearances of spontaneous bacterial peritonitis would certainly be an interesting audit to compile.
US can play a triaging role for several additional pathologic conditions that may occur in the peritoneum. These include inflammatory disease processes such as epiploic appendagitis or omental infarction (3,4), in which the clinical acumen of the sonologist may be particularly helpful for suggesting a diagnosis and in limiting subsequent unnecessary interventions. The preceding article described some of the intraperitoneal manifestations of lymphoma. Identification of hypoechoic mesenteric nodes or a more solid hypoechoic mesenteric mass encircling mesenteric vessels or bowel loops may well suggest the diagnosis of lymphoma. In this setting, US can clearly play a large role in suggesting the diagnosis of lymphoma and in guiding fine-needle aspiration for flow cytometry.
To further complement the preceding article, it is also worth considering the useful role played by the spectrum of US-guided interventional procedures. These commonly encompass fluid aspiration or therapeutic drainage, biopsy or fine-needle aspiration of solid masses, and catheter insertion and placement. Although US is used for cyst drainage, the precise indications and optimal techniques are not universally defined. Similarly, the role of US and optimal techniques for sclerosing peritoneal cysts remain to be better defined. The intraperitoneal procedure that may well be used with increasing frequency in the future is laparoscopic US, which is specifically used to facilitate biopsy and surgical procedures. An additional opportunity for interventional US in the peritoneum may well encompass catheter insertion for peritoneal dialysis or even malignant ascites (5).
In conclusion, the authors have produced a succinct and comprehensive audit of the US spectrum of peritoneal disorders, which is a valuable addition to the abdominal imaging literature.
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