Right iliac fossa pain is a common presentation to the emergency department. Although appendicitis is the most common surgical emergency, there are many other causes of right iliac fossa pain that must be considered when evaluating these patients [Table 1]. Ultrasound is frequently recommended as the primary imaging modality for the investigation of acute abdominal pain, especially in young patients, and can often demonstrate the cause of the pain in these patients. This article will describe some of the pathologies, other than appendicitis, that can present as right iliac fossa pain, and that may be seen when scanning a patient for “query appendicitis.”
Infectious colitis and gastroenteritis generally present with more diarrhea and vomiting than usually occurs in appendicitis, but there can be considerable overlap in patient symptoms. Ultrasound findings consist of thickened bowel wall, which may show hyperemia. The normal bowel wall thickness is <3 mm. Focal inflammation of the adjacent bowel can occur with appendicitis, but in infectious colitis, the thickened area of the bowel extends beyond the region of the appendix, and a normal appendix may also be seen [Figure 1 and https://links.lww.com/JMUT/A51]. Other causes of colitis (such as ulcerative colitis) may give similar appearances but can usually be distinguished clinically.
Terminal ileitis can be due to infectious causes and Crohn's disease. Thickened bowel (>3 mm) may be seen in both causes. Crohn's disease may also show loss of the bowel wall layers, creeping fat, strictures, and other complications of inflammatory bowel disease, but ultrasound may not be able to distinguish between infectious and inflammatory bowel disease. In susceptible patients, tuberculosis can also cause terminal ileitis [Figure 2].
In Western populations, diverticulitis is typically seen in the descending and sigmoid colon and only uncommonly occurs in the cecum or ascending colon. Right-sided diverticulitis is more common in oriental populations, where it typically occurs in younger patients and is often misdiagnosed initially as appendicitis. Ultrasound findings are similar to left-sided diverticulitis with an outpouching of the bowel containing echogenic material, diverticular wall thickening, and surrounding echogenic fat at the point of maximal tenderness [Figure 3 and https://links.lww.com/JMUT/A52].
Meckel's diverticulum occurs in approximately 2% of the population, and if it becomes inflamed, it can mimic appendicitis. Ultrasound findings are similar to other forms of diverticulitis or appendicitis (thick-walled, cystic mass with adjacent echogenic fat), but the diverticulum cannot be traced to the cecum but instead arises from the distal ileum. More frequently, Meckel's diverticula can present with gastrointestinal bleeding (due to gastric heterotopic gastric tissue) or bowel obstruction related to intussusception or remnant bands.
Intussusception is classically seen in young children, who may or may not be able to localize their pain when the ileum invaginates into the colon (ileocolic intussusception). It is the most common cause of small-bowel obstruction in children. Ultrasound shows a thickened, multilayered appearance of bowel within bowel, described as an “onion” or “target” sign when viewed in transverse orientation. Centrally, there will be a crescentic hyperechoic region due to invaginated mesentry [Figure 4 and https://links.lww.com/JMUT/A53]. There is increasing recognition of short segment, brief, transient, self-resolving ileoileal intussusception without an identified lead point, which may be incidental or occur in association with many other conditions (due to hyperperistalsis, lymphoid hyperplasia, focal wall thickening, etc.). As this type of intussusception is self-resolving, it does not have the same treatment implications as either persisting intussusception or ileocolic intussusception.
Multiple enlarged (>8 mm in short axis of at least one) lymph nodes may be due to presumed viral infection and are a common cause of right iliac fossa pain in children [Figure 5 and https://links.lww.com/JMUT/A54]. However, reactive lymph nodes can occur in association with many conditions (including appendicitis), so careful examination to exclude other pathologies should be performed before concluding the pain is due to mesenteric adenitis.
Epiploic appendagitis is due to the infarction of an epiploic appendage, usually due to torsion or thrombosis of its feeding vessels. Ultrasound shows a tender, hyperechoic, avascular, ovoid mass surrounded by a hypoechoic rim that is typically 2–4 cm and attached to the parietal peritoneum [Figure 6]. As thrombosis of the feeding vessels may be secondary to the inflammation of nearby structures, careful examination for other pathologies should be performed.
RIGHT RENAL COLIC AND PYELONEPHRITIS
Although the clinical presentation of renal colic is typically different (flank pain and microscopic hematuria), a distal ureteric stone may present as right iliac fossa pain. Ultrasound generally shows hydronephrosis and an echogenic, shadowing stone may be seen in the ureter [Figure 7].
Similarly, the clinical presentation of pyelonephritis is usually evident; however, it should be remembered that appendicitis may occasionally cause leukocytes in the urine (especially if the inflamed appendix is lying adjacent to the bladder). Ultrasound in pyelonephritis is generally normal but may show either hypoechoic or hyperechoic segmental areas and an area of reduced color Doppler flow [Figure 8]. Ultrasound can also be useful to detect hydronephrosis or abscess formation.
Ovarian pathologies, such as hemorrhagic cysts, cyst rupture, and torsion, may all present as right iliac fossa pain in female patients, although usually with a more rapid onset of pain. Ovarian torsion, in particular, can be a difficult clinical and sonographic diagnosis with varied clinical presentation (vomiting is reported between 30% and 80% and pain levels can fluctuate). Sonographic features are classically an enlarged, edematous ovary with prominent follicles due to hyperechoic rims [Figure 9 and https://links.lww.com/JMUT/A55], and a focal ovarian mass (e.g., cyst). The ovary may be in an abnormal position. A “whirlpool sign” of the twisted pedicle has high specificity but poor sensitivity. It should be remembered that the presence of color Doppler flow is seen in half of (surgically proven) ovarian torsion cases, and spectral Doppler may reveal both arterial and venous flow.
ABDOMINAL WALL PATHOLOGY
Right-sided rectus sheath hematomas typically occur in anticoagulated patients and cause focal tenderness. They appear as lens-shaped mass in the anterior abdominal wall, contained by the rectus sheath and may be anechoic, show heterogeneous echogenicity, or a fluid–fluid level [Figure 10].
Psoas abscesses can occur from primary hematogenous seeding or secondary to spread from adjacent infection. If right sided, it can cause right iliac fossa pain and tenderness, classically associated with hip pain. Ultrasound demonstrates a heterogeneous mass within the psoas muscle with a loss of the normal muscle striation [Figure 11a and b].
Appendicitis is a common cause of right iliac fossa pain, but there are many other causes that must be considered. While the history and clinical examination will generally guide the differential diagnosis, there is often overlap of the findings, so ultrasound can be extremely useful in these patients. In particular, if ultrasound demonstrates a normal appendix, or the appendix is not seen, then other causes should be considered and specifically examined for.
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