Traditional laboratory studies, such as a CBC, serum chemistries, and urinalysis, are routinely ordered but are of minimal value in the evaluation unless seeking an alternative diagnosis or for preoperative clearance.
Plain films are not required in hernia patients without significant symptoms. The acute abdominal series can reveal the presence of free air and signs of intestinal obstruction, but otherwise, plain films are usually indeterminate or nondiagnostic.
US has many advantages including low cost, no ionizing radiation, ready availability, no contrast agents used, and ability to be performed at the bedside. However, US is both operator and body habitus dependent. The primary role of US is the identification of the hernia itself. The dynamic abdominal sonography for hernia examination has good results in the hands of surgeons as compared to CT for the diagnosis of hernia.15 When a hernia is identified by US, note hernia size, contents, reducibility, location of the facial defect, and tenderness.16 In addition to determining whether bowel is present in a hernia sac, US can sometimes identify signs of incarceration and strangulation.16,17,18 Strangulated bowel, by definition, has vascular compromise. In the natural history of an incarcerated hernia, the thin-walled veins and lymphatics become compressed and compromised before the thick-walled arterial supply. Doppler US can detect the arterial flow to the loop of bowel but is usually not sensitive enough to detect venous flow and cannot detect lymphatic flow. Thus, Doppler US can be insensitive for strangulation.16,17,18 However, preservation of arterial inflow with obstruction of venous outflow causes increased intravascular pressure and extravasation of fluid into the extracellular space. This manifests itself as free fluid in the hernia sac on B-mode US, which is a sensitive finding for incarceration and strangulation. The specificity of free fluid in the hernia sac is good per se, but may be confounded by patients with ascites. Other US findings associated with incarceration and strangulation include hyperechoic fat, isoechoic thickening of the hernia sac, thickening of the wall of the herniated bowel, and free fluid within the herniated bowel loop.16,18 Absence of peristalsis in a herniated bowel loop is suggestive of incarceration, and the presence of peristalsis implies that bowel resection is less likely to be necessary when the patient undergoes operative intervention.18 US is most useful for diagnosis in children and pregnant women given its lack of ionizing radiation.12
It can be clinically difficult to differentiate hernia from hydrocele when assessing a scrotal mass. Obtaining a scrotal US in the standing position, with and without Valsalva maneuver, is a good way to demonstrate hernia.
CT is the best-performing radiographic test for hernia diagnosis and can identify uncommon hernia types (e.g., Spigelian or obturator) as well as demonstrate incarceration and strangulation.19