Pitfalls in CT diagnosis of appendicitis: Pictorial essay

Authors


  • Conflict of interest: None.

Correspondence

Dr Ashkan Shademan, Department of Medicine, Penn State Hershey Medical Center, Mail Code H039, 500 University Drive, Hershey, PA 17033, USA.

Email: ashademan@hmc.psu.edu

Summary

Despite the high diagnostic accuracy of CT for appendicitis, numerous pitfalls exist that may result in a misdiagnosis. This pictorial review outlines the potential pitfalls in the CT diagnosis of appendicitis that includes atypical position of the appendix and coexisting pathologies. Various mimickers of appendicitis and clinical dilemmas will be highlighted. Upon completion, the reviewer should have an improved ability to recognise appendicitis mimickers and identify equivocal or atypical findings.

Introduction

Acute appendicitis is the most common cause of acute abdominal pain that requires surgery in adult. Typical presentation includes right lower quadrant abdominal pain, anorexia, nausea and vomiting. Various overlapping clinical features exist between appendicitis and other diseases that may result in a clinical misdiagnosis.[1] Atypical presentation of appendicitis due to different positions of the appendix or coexisting pathologies can also complicate the diagnosis.[2]

Worldwide, CT and ultrasound of the abdomen are the two most commonly used imaging modalities for diagnosing acute appendicitis.[3] The sensitivity and specificity of CT for acute appendicitis is reported between 91 and 98 and 75 and 93 percent, respectively.[4, 5] Ultrasound is widely used in paediatric and young female patients to avoid radiation exposure. MRI is an alternative modality in pregnant patients when ultrasound is equivocal.[3]

The sensitivity and specificity of the individual CT signs of appendicitis have been studied in proven cases, with the most reliable sign being the maximal cross-sectional appendiceal diameter. Other helpful predictive signs include maximal luminal diameter of the appendix, peri-appendiceal inflammatory changes, maximal wall thickness of the appendix and presence of peri-appendiceal fluid (Table 1).[6] A number of inflammatory or neoplastic processes involving the appendix or adjacent structures mimic appendicitis or its complications on CT scan.[7] Such incorrect diagnoses may lead to a delayed management of the existing disease, unnecessary intervention or hospitalisation. This pictorial review categorises these pitfalls that can render the diagnosis of appendicitis challenging on CT scan.

Table 1. Sensitivity and specificity of individual CT signs of appendicitis
CT findingSensitivity (%)Specificity (%)
Maximal cross-sectional diameter90.291.5
Maximal luminal diameter63.491.5
Peri-appendiceal infiltrates53.794.9
Maximal wall thickness48.893.2
Peri-appendiceal fluid22100

Discussion

Although CT has high accuracy for diagnosing appendicitis, many pitfalls exist. For the purpose of this pictorial review, these are divided into appendicitis mimickers on CT, diagnostic dilemmas, atypical clinical presentations due to anatomical variations and concurrent pathologies.

Appendicitis mimickers on CT

Assuming a normal appendix is not found in CT, various conditions may be misdiagnosed as acute appendicitis.

Right-sided colonic diverticulitis is a common clinical mimicker of acute appendicitis that may also be mistaken with appendicitis on CT scan by causing peri-colic inflammatory changes and adjacent colonic wall thickening.[1] The presence of normal appendix makes appendicitis unlikely (Fig. 1a); however, when the appendix is not visualised, appendicitis cannot be ruled out (Fig. 1b).

Figure 1.

Cecal diverticulitis with (a) and without (b) visualisation of the appendix. (a) Forty-two-year-old man with acute right lower quadrant pain and fever. Enhanced CT shows mesenteric stranding centred on a hyper-dense diverticulum (arrow) arising from the cecum. Adjacent retro-cecal appendix (arrowhead) is slightly dilated in calibre and contains scattered foci of air with adjacent peri-cecal stranding. (b) Thirty-five-year-old woman with acute right lower quadrant pain. Enhanced axial CT reveals peri-cecal stranding with small cecal diverticulum (arrow). When the appendix is not seen, cecal diverticulitis can be misdiagnosed as acute appendicitis.

Meckel's diverticulum is a tubular structure, containing air and fluid that is connected with the adjacent small bowel. In addition to morphologic similarities with the appendix, inflammation of the Meckel's diverticulum may occur by obstruction of the orifice.[8] With incomplete or no visualisation of appendix, Meckel's diverticulitis is a potential mimicker for acute appendicitis (Fig. 2).

Figure 2.

Thirteen-year-old female with ruptured Meckel's diverticulum. (a) Axial post-contrast CT shows an air-containing fluid collection surrounding a thickened tubular soft tissue density structure (arrow) in the right lower quadrant. (b) Coronal post-contrast CT shows the fluid collection and the tubular density with surrounding fluid (arrow) adjacent to loops of small bowel. Pathology confirmed inflammation and rupture of Meckel's diverticulum with normal appendix.

Cecal carcinoma can manifest as a discrete mass that may lead to appendiceal dilatation, peri-appendiceal fluid collection and colonic wall thickening on CT (Fig. 3). Obstructive appendicitis may occur as a result of cecal tumour. However, in some cases of colon cancer, appendiceal changes such as appendiceal dilation and wall thickening, without appendicitis, may be the dominant CT finding.[7] Although obstruction of appendix is a predisposition for acute inflammation, without clinical signs and symptoms, these incidental CT findings could be followed-up without the need for surgery.

Figure 3.

Sixty-eight-year-old woman with large cecal adenocarcinoma with secondary appendiceal obstruction and dilatation. Coronal CT with oral and IV contrast shows a large cecal mass (arrow) as well as dilated appendix measuring 1 cm in diameter (arrowhead). In view of acute right lower quadrant pain, right hemicolectomy was perfumed. Pathology confirmed cecal adenocarcinoma; however, the appendix was dilated without inflammatory changes. In this case, the cecal wall thickening is mass like and too extensive for secondary changes of appendicitis. Some degrees of peri-cecal fat stranding due to lymphatic congestion is expected in carcinoma and is therefore an unhelpful differentiator. However, the appendiceal changes may potentially lead to an incorrect diagnosis of acute appendicitis.

An appendiceal mucocele represents an appendix distended with intra-luminal mucus, secondary to chronic obstruction of the appendix, mucosal hyperplasia and benign or malignant neoplasms of the appendix.[9] A substantial proportion of mucoceles and mucinous adenomas present clinically with obstructive appendicitis.[10] The typical CT finding of a mucocele is a low attenuation, encapsulated cystic mass without wall thickening or stranding.[9] Appendiceal dilation with surrounding stranding can mimic features of acute appendicitis (Fig. 4).

Figure 4.

Fifty-three-year-old woman with mucocele secondary to mucinous cystadenoma. Axial CT with oral and IV contrast shows a dilated large fluid filled appendix (arrow). Peri-appendiceal stranding appears posteriorly, which is an atypical feature of mucinous cystadenoma. In conjunction with acute right lower quadrant abdominal pain, acute appendicitis appeared likely. The patient underwent appendectomy, which revealed mucinous cystadenoma with no appendicitis.

Gynaecologic pathologies such as pelvic inflammatory disease and haemorrhagic functional ovarian cyst can manifest as appendicitis by causing acute right lower quadrant abdominal and pelvic pain.[1, 4]Ultrasound is preferred as the first-line modality in young females with lower abdominal or pelvic pain. When ultrasound is negative or equivocal, a CT can be performed for further evaluation. Occasionally, pelvic MRI can be helpful as a problem-solving tool in difficult cases. In exceptional circumstances, diagnostic laparoscopy is performed when imaging and clinical picture are inconsistent.[3]

Another cause of thickened appendix mimicking appendicitis is Crohn's disease. Appendiceal changes are seen in approximately 20% of patients undergoing surgery for Crohn's disease.[11] Appendiceal changes occur due to surrounding inflammatory changes or as a direct extension of Crohn's disease.[12] Ileal, cecal and appendiceal wall thickening with associated inflammatory changes or fibro fatty proliferation of the adjacent mesentery is seen in both conditions[12, 13] (Fig. 5). It is important to note that appendiceal abnormalities seen in these circumstances are most commonly secondary changes of Crohn's disease, which on their own, are not an indication for surgery.

Figure 5.

Eighteen-year-old man presented with right lower quadrant pain. The patient underwent ileocolectomy, and pathology was consistent with active Crohn's disease with fissures. Despite appendiceal changes on CT scan, no pathologic alteration of the appendix was reported on pathology. (a) Coronal enhanced CT showing extensive inflammation of the terminal ileum, cecum and ascending colon with surrounding mesenteric oedema and free fluid (arrow), consistent with Crohn's disease. (b) Axial enhanced CT shows a mildly distended appendix measuring 4 m with hyper-enhancing wall (arrow).

Epiploic appendagitis is a self-limited disease that results from venous occlusion of epiploic appendages.[14] CT features include a low-attenuation oval fatty mass, and when it occurs in the right lower quadrant is accompanied with stranding mimicking CT features of appendicitis (Fig. 6).

Figure 6.

Thirty-five year-old man with epiploic appendagitis presenting with right lower quadrant abdominal pain. CT with oral and IV contrast shows an oval-shaped inflammatory mass (arrow) with central density and mild fat stranding in keeping with epiploic appendagitis. As the appendix was not identified and clinical manifestations were highly suggestive of appendicitis, the patient underwent appendectomy. Infarction and inflammation of appendix epiploica, with no alteration of the appendix, was seen on pathology. Non-visualisation of the appendix with typical clinical presentation of appendicitis can cause a diagnostic dilemma for the surgeon despite the presence of an alternative diagnosis on CT.

Amyand hernia is a rare type of inguinal hernia defined by presence of appendix in inguinal canal. It occurs in 1% of all inguinal hernias, and acute appendicitis with appendix incarceration is a recognised complication. Assessment of the appendix can be challenging due to lack of surrounding fat[14] (Fig. 7).

Figure 7.

Fifty-nine-year-old man with right lower quadrant abdominal pain and thickened appendix within right inguinal hernia. (a) Axial, enhanced CT shows herniation of the distal appendix (arrow) into the right inguinal canal (amyand hernia). (b) Axial, enhanced CT at a lower level shows increased soft tissue density around the distal appendix (arrow), which is dilated and suggestive of tip appendicitis. Pathology revealed a normal appendix within the right inguinal canal. (c) Coronal, enhanced CT shows tubular structure of appendix within the inguinal canal (arrow).

Diagnostic dilemmas

Equivocal cases of appendicitis, where only one feature is present, are observed frequently. This makes the diagnosis more challenging. Therefore, clinical correlation is essential in these cases. Appendicitis is encountered in about 30% of patients with equivocal CT findings.[15] Non-visualisation of appendix is present in 5 to 10% of CT examinations and can create a unique diagnostic challenge in patients with suspected appendicitis.[16] It is important to know that up to 40–50% of patients with right lower quadrant stranding or fluid collection, but non-visualisation of the appendix, end up with pathologic diagnosis of appendicitis.[7, 15] Early appendicitis can present with mild abdominal pain with normal appearing appendix on CT.

Tip appendicitis is inflammation of distal appendix with sparing of the proximal portion. Following the whole length of the appendix until identification of the blind end can prevent a missed diagnosis (Fig. 8).[17]

Figure 8.

Eighteen-year-old man with acute right lower abdominal pain and guarding, with tip appendicitis. (a) Although clinical findings were highly suspicious of acute appendicitis, enhanced axial CT demonstrating the proximal part of appendix that is filled with contrast material and contains air (arrow). (b) Enhanced axial section of the appendiceal tip shows subtle wall thickness and absence of the contrast agent (arrow).

Atypical clinical presentations due to anatomical variations

Due to anatomical variations of appendix, approximately one-third of patients with acute appendicitis present with abdominal pain, which is not localised in right lower quadrant.[4] Common atypical locations of the appendix include right upper and left lower quadrant pain. Variable location of the appendix is usually due to both inconsistent position of the cecum and free end of appendix in relation to cecum[4] (Fig. 9a). Some of the congenital anomalies, such as malrotation, are also responsible for atypical positioning of the appendix (Fig. 9b). Atypical location of the appendix can also be a problem in pregnancy due to rotation of the cecum with an expanding uterus.[18]

Figure 9.

Atypical location of the appendix. (a) Forty-nine-year-old woman with acute appendicitis, presenting with left-sided, lower quadrant abdominal pain. Axial CT with oral and IV contrast shows a dilated thickened appendix crossing the midline into the left lower quadrant (arrow). (b) Twenty-five-year-old woman with malrotation, who underwent abdominal CT due to colitis. Ileocecal region (arrow) and normal appendix (arrowhead) are seen in the left lower quadrant.

Concurrent pathologies

Diagnosis of acute appendicitis may be difficult when another disease is also present.[4] The coexisting disease process can be acute, such as diverticulitis (Fig. 10) or cholecystitis (Fig. 11), or longstanding process such as primary neoplasm of appendix (Figs 12, 13). It is often not possible to identify appendix or cecal tumour that is the underlying cause of appendicitis.

Figure 10.

Sixty-seven-year-old man with concurrent appendicitis and diverticulitis presenting with acute severe lower abdominal pain and guarding. (a) Enhanced axial CT demonstrates sigmoid diverticulum with stranding (arrow). (b) Enhanced axial CT shows a dilated appendix with appendicolith (arrow). No stranding was detected on this study. Radiologist suggested that appendiceal changes could be chronic due to mucocele. (c) The patient was treated medically for diverticulitis with antibiotics. Follow-up enhanced axial CT after 2 days demonstrates resolution of sigmoid diverticulitis. (d) Enhanced axial images of the appendix in follow-up CT scan after 2 days (same scan as c) shows stranding of the thick-walled appendix (arrow). Acute appendicitis was confirmed after appendectomy performed on the same day.

Figure 11.

Twenty-nine-year-old man with concurrent appendicitis and cholecystitis presenting with nausea, vomiting, fever and right upper quadrant pain. Patient underwent cholecystectomy and appendectomy. Pathology revealed appendicitis and chronic cholecystitis with cholelithiasis. (a) Contrast-enhanced CT shows minimally enlarged appendix (arrow), measuring 8 mm in diameter. (b) Contrast-enhanced CT shows minimal peri-appendiceal stranding and fluid in inferolateral aspect of the cecum with conal fascials thickening (arrow). (c) Contrast-enhanced CT shows markedly thickened and edematous gall bladder wall (arrow) and peri-cholecystic fluid, consistent with cholecystitis. Although the clinical and radiological findings are consistent with acute cholecystitis, the appendiceal findings should not be attributed to secondary changes.

Figure 12.

Fifty-seven-year-old man with appendicitis and appendicular carcinoid. (a) Contrast-enhanced CT shows stranding, surrounding the appendix (arrow). (b) Contrast-enhanced CT shows the dilated appendix (arrow) and adjacent mildly enlarged nodes (arrowhead). (c) Arterial phase contrast-enhanced axial CT shows a small hyper vascular liver lesion, consistent with hyper vascular metastasis (arrow).

Figure 13.

Fifty-eight-year-old man with adenocarcinoma of the appendix and acute appendicitis. Contrast-enhanced CT shows dilated appendix with marked wall thickening (arrow) and prominent lymph node (arrowhead) with adjacent fat stranding and inflammatory changes.

Conclusion

Various pitfalls exist in the CT diagnosis of appendicitis that may lead to a misdiagnosis. In addition, atypical location of the appendix or coexisting pathologies makes precise diagnosis more challenging. Familiarity with these conditions, as presented in this pictorial review, is important for an accurate diagnostic approach, prompt management and avoidance of unnecessary procedures.

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