Beyond acute appendicitis: imaging of additional pathologies of the pediatric appendix
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- Dietz, K.R., Merrow, A.C., Podberesky, D.J. et al. Pediatr Radiol (2013) 43: 232. doi:10.1007/s00247-012-2565-1
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Primary acute appendicitis is by far the most common pathological condition affecting the appendix. There are differential diagnoses, however, when an abnormal appendix is found by imaging. The purpose of this paper is to highlight the imaging and clinical manifestations of less common appendiceal abnormalities in children. Familiarity with these alternative diagnoses might be particularly helpful in guiding management of the child whose clinical presentation is not typical for primary acute appendicitis.
KeywordsAppendixAppendicitisAppendiceal neoplasmCystic fibrosisChildren
Primary acute appendicitis, defined as appendiceal inflammation caused by appendiceal obstruction and superimposed bacterial infection, is by far the most common pathology of the appendix. Imaging evaluations to exclude this diagnosis occur daily in the pediatric radiology setting. The clinical and imaging differential diagnosis in a child with right lower quadrant pain and suspected appendicitis is a broad but well-recognized list that predominantly involves structures adjacent to the appendix such as the ovaries, small bowel, large bowel and urinary tract. There are, however, less common pathologies involving the appendix that can create an imaging diagnostic dilemma in the setting of right lower quadrant symptoms. Some of these entities merely mimic appendicitis by imaging or clinical presentation. Others lead to a secondary appendicitis, though the causal relationship between the underlying pathology and the inflammation is often unclear.
The abnormally thickened luminal contents found in children with cystic fibrosis (CF) can result in chronic distention of an otherwise normal appendix. The majority of asymptomatic CF patients have an appendix ≥ 6 mm in diameter by US (with a mean of 8.3 mm), whereas the generally accepted upper limit of normal in an otherwise healthy child is < 6 mm .
Additionally, children with CF have a lower incidence of acute appendicitis compared with the general population(1–2% versus 7%) . It is hypothesized that the inspissated secretions in the appendix actually protect against appendicitis. However, children with cystic fibrosis who develop acute appendicitis are more likely to experience complications such as perforation caused by a delay in diagnosis .
While uncomplicated primary appendicitis most commonly exhibits isolated appendiceal inflammation without thickening of the adjacent bowel, appendiceal inflammation in the setting of Crohn disease is usually seen with concurrent cecal or terminal ileal involvement. Crohn disease isolated to the appendix, while uncommon, has a favorable prognosis over that affecting the ileum or colon, with recurrence rates of up to 8% . Follow-up of these children is controversial, with some thought that appendectomy might be curative .
One of the hallmarks of ulcerative colitis is its continuous involvement of the colon; however, children can have discontinuous involvement (i.e. a “skip lesion”) in the appendix .
Hirschsprung disease and the appendix (Fig. 7)
Neonatal appendicitis is very rare with high rates of perforation (82.5%) and mortality (28%) [5, 6]. It is most commonly associated with prematurity (possibly resulting from necrotising enterocolitis), inguinalhernias (i.e. the Amyand hernia), cystic fibrosis and Hirschsprung disease [5, 6]. Rectal suction biopsies and placement of a decompressing cecostomy should be considered at the time of appendectomy as long-segment or total-colonic Hirschsprung disease can present as neonatal appendicitis .
The Amyand hernia, an inguinal hernia containing the appendix, is very uncommon. The entity is named after Claudius Amyand, the surgeon who reported the first successful appendectomy in 1735 on a boy with appendiceal perforation in an inguinal hernia secondary to an ingested pin .
The reported incidence of a normal appendix in an inguinal hernia is 0.5–1.0% . Amyand hernias are most commonly seen on the right side given the usual right lower quadrant location of the appendix. If an Amyand hernia is seen on the left, then situs inversus, intestinal malrotation or a mobile cecum should be considered .
Occasionally, the Amyand hernia contains an inflamed appendix (0.1% of inguinal hernia cases) . Preoperative diagnosis of herniated appendicitis can be difficult because of its overlapping presentation with an incarcerated or strangulated inguinal hernia .
As noted previously, acute appendicitis is uncommon in neonates and is usually associated with underlying pathology. One review showed that 29 of 111 cases of neonatal appendicitis arose in an inguinal hernia and that this particular subset of neonatal appendicitis cases had an improved prognosis versus other etiologies, likely because of the operative implications of a clinically apparent incarcerated inguinal hernia .
Intussusception of the appendix can occur in isolation (e.g., appendiceal inversion or invagination into the cecum, which can be incidental or caused by an appendiceal lesion) or as part of an ileocolic intussusception. The appendix serves as a pathological lead point in approximately 0.2% of all ileocolic intussusception cases .
Approximately 25% of isolated appendiceal intussusception (or inversion) cases occur in children, but the appendix is more likely to be inflamed in children with this entity (76%) than in adults (19%) .
Of note, it is unclear whether all reported cases of appendicitis found in intussusception truly represent inflammation or infection rather than secondary vascular congestion or edema.
Malignant neoplasms involving the appendix are rare, found in only 0.9–1.4% of appendectomy specimens. Most cases are not diagnosed preoperatively . Carcinoid tumors are by far the most common malignancy of the appendix and much more commonly present with acute appendicitis than with carcinoid syndrome .
Laparoscopic resection is considered safe in adults given that appendiceal carcinoids are relatively indolent malignancies overall. This has not been evaluated in children, in whom carcinoid tumors have been found to be more aggressive (because of an increase in serosal and fat involvement) . However, because small carcinoids (the majority of lesions) are unsuspected preoperatively, they are often removed laparoscopically in children as well. In general, appendectomy is considered curative for carcinoid tumors confined to the appendix that are less than 2 cm in size .
Mucocele of the appendix (Fig. 15)
Mucoceles of the appendix are rare, found in only 0.25% of appendectomy specimens . They are more commonly found incidentally (e.g., during elective appendectomy in gynecological cases) than in cases of suspected appendicitis. Mucoceles of the appendix are most common in adults and are rarely seen in adolescents .
Mucoceles are described on a benign to malignant histological spectrum from simple mucocele to mucinous cystadenoma to mucinous cystadenocarcinoma. Caution should be taken in performing appendectomies for suspected mucoceles given an elevated risk historically of port-site recurrences and pseudomyxoma peritonei .
Lymphoma of the appendix (Fig. 16)
Appendiceal involvement in non-Hodgkin lymphoma is rare, occurring in 1–3% of all non-Hodgkin patients . Burkitt lymphoma is the most frequent pediatric subtype of non-Hodgkin lymphoma overall (34%) and can occur anywhere, though it is most common in the ileocecal region in children . Nearly all reported pediatric cases of appendiceal lymphoma are caused by the Burkitt subtype . Of note, Burkitt lymphoma is a rapidly growing tumor with the potential to double in size in 24 h .
The appendix can become impacted with non-shadowing fecal material in the normal patient, resulting in enlargement and a diminished compressibility suggestive of appendicitis. The presence of an intact appendiceal wall and lack of surrounding fluid and fat inflammation, in conjunction with the clinical and laboratory findings, can provide reassurance that the appendix is normal .
Of note, this appearance may represent the modern imaging equivalent of the appendiceal fecal casts described on barium enemas and, under great controversy, publicized as a finding of “appendiceal colic” by Schisgall  in the 1980s. Appendiceal colic is described as recurrent lower abdominal pain in children attributable to contractions of the appendix attempting to expulse hardened fecal material [20, 21]. Though little has been published on appendiceal colic in recent years, the existence of this entity remains debated with some surgical reports of pain relief from appendectomy in this setting .
Appendicoliths (Fig. 19)
The significance of a calcified appendicolith in an otherwise normal appendix has been a long-standing source of controversy, mainly in regard to: (1) the unclear association with chronic pain, and (2) the likelihood of ultimately developing appendicitis. Recent literature suggests that children with appendicoliths found in otherwise normal appendices by CT are at no increased risk of developing acute appendicitis [24, 25]. However, a few such cases that have undergone prophylactic appendectomy have shown inflammation on pathological examination. Interestingly, one of these papers reported that 64% of such patients who underwent follow-up imaging without interval appendectomy no longer showed an appendicolith, though the size of those initial appendicoliths was not published .
Foreign bodies in the appendix (Fig. 20)
Almost 95% of swallowed foreign bodies pass through the gastrointestinal tract without incident . A 1971 study showed that 0.0005% of patients developed appendicitis from foreign bodies. This was down from 3% during 1923–1962, likely because of a decreased use of sewing pins and a decreased consumption of wild game hunted with buckshot/birdshot . Colonoscopic removal of appendiceal foreign bodies has been described in adults .
Parasites and the appendix (Fig. 21)
A variety of parasites can be found in the appendiceal lumen, including Enterobius vermicularis (pinworms), Ascaris lumbricoides (roundworms) and Entamoeba histolytica. Pinworms are found in the gastrointestinal tracts of 4–28% of children worldwide with the highest prevalence in 5- to 10-year-olds. Pinworms are found in 0.6–13% of resected appendices (including those without inflammation) . Given that they are not typically invasive, however, the role of pinworms in appendicitis is unclear.
Other appendiceal abnormalities (not shown)
A secondary inflammation of the appendix can occur with other adjacent inflammatory processes such as neutropenic colitis and tubo-ovarian abscess. A recent retrospective study attempting to differentiate tubo-ovarian abscess from acute appendicitis by CT showed an abnormal appendix by imaging in 2% of confirmed tubo-ovarian abscess cases .
Appendiceal inflammation has rarely been reported concomitantly with ovarian torsion, though it is not clear from all published reports whether true primary inflammation of the appendix was present histologically rather than secondary to changes of vascular congestion or ischemia. In fact, one case reported twisting of the ovary around the appendix with necrosis of the appendiceal tip .
Isolated torsion of the appendix has also been described with and without underlying pathology, most frequently in adults. Fewer than 15 pediatric cases have been reported in the literature, including two infantile cases. One of these was recently reported in an 11-week-old girl with peritoneal signs and a sonographically distended, non-compressible appendix that was found to be torsed and necrotic intraoperatively with gangrenous appendicitis found upon pathological examination .
Despite the frequency of primary acute appendicitis, there are differential diagnoses when an abnormal appendix is found by imaging. Familiarity with these alternative diagnoses may be particularly helpful in guiding management of the child whose clinical presentation is not typical for primary acute appendicitis.
Conflicts of interest
The following coauthors have relevant financial relationships or potential conflicts of interest related to the material: A.C. Merrow is an author and content manager for Amirsys Inc.; D.J. Podberesky is on the speaker’s bureau for Toshiba of America Medical Systems; A.J. Towbin is an author for Amirsys Inc.