Brian P. Jacob, David C. Chen, Bruce Ramshaw, Shirin Towfigh (eds.) - The SAGES Manual of Groin Pain-Springer International Publishing (2016)

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J.M. Miller et al.
Knowing the limitations of a given study in advance can improve diagnostic
accuracy and help set patient expectations accordingly, thus preventing
the frustration elicited by unanticipated follow-up exams.
Regardless of the modality chosen, the more information provided to the
radiologist, the more specific the interpretation can be: while “pain” is a
valid indication, lateralizing and characterizing the pain (e.g., “sharp left
groin pain with defecation”) can assist with selection of proper image
acquisition protocols and winnow down the list of potential pathologies
that may present with similar appearances.
Computed Tomography /Radiography (X-ray)
An X-ray tube generates radiation by smashing high-energy electrons
into a durable piece of metal that can resist melting from the consequent
heat exchange. The process is known as the photoelectric effect , and
underlies a number of modern technologies like solar panels and digital
cameras. X-rays passing through the body have a probability of being
scattered or absorbed that is related to tissue density; that probability of
being attenuated by tissue allows for the discrimination of fluid, fat, soft
tissue, and bone. The amount of attenuation can be quantified on a relative
scale quantified by the Hounsfield Unit, where air is arbitrarily
defined as −1000 HU and water as 0 HU, with the implication of an
upper bound of +1000 HU for bone. While these values are only explicitly
measured for CT, they are still an important factor in conventional
radiography.
On conventional radiographs, the differentiation of two structures
relies on a sufficient discrepancy between their attenuations: air-filled
bowel can be easily seen against the background of the peritoneum,
while fluid-filled bowel is too similar to distinguish. Musculoskeletal
abnormalities that may cause groin pain, such as femoral acetabular
impingement (FAI), spondylosis/spondylolisthesis of the lumbosacral
spine, sacroiliitis, slipped-cap femoral epiphysis, hip osteoarthritis, calcific
tendonitis, and fracture, can all be reasonably eliminated from a
differential diagnosis on the basis of radiography, provided that the
proper views are acquired and that technical factors (such as patient’s
body habitus) allow (Figs. 13.1 , 13.2 , and 13.3 ). The gold standard in the
evaluation of inguinal hernia, i.e., herniography—the injection of contrast
material into the peritoneal cavity followed by radiography of the
groins—is rarely performed these days outside of a few specialized