Teaching Case

A 53-year-old man was admitted to our emergency department because of a 24-hour history of right flank pain. No fever or vomiting was described. Abdominal examination showed tenderness in the right iliac fossa with positive Blumberg sign.

The only laboratory abnormality was a mild elevation of C Reactive Protein.

Contrast-enhanced CT revealed an enlarged appendix (2 cm diameter, short axis) with irregular wall thickening and diffuse stranding of the adjacent mesenteric fat.

Mild ascites in the right paracolic gutter and 2-3 small pericecal lymph nodes were also noted.

No pneumoperitoneum or other small bowel or colonic abnormality were seen.

The patient was submitted to an appendicectomy with symptomatic resolution. The macroscopic features of the appendix were also consistent with an acute appendicitis, according to the surgeons. However, ​​the final histopathological diagnosis, apart from inflammatory findings, was well-differentiated nonmucinous adenocarcinoma of the appendix stage III (pT3 pN1a).

Appendiceal neoplasms are uncommon tumours found in approximately 1% of appendicectomy specimens. Approximately 30%–50% of these tumours will manifest acutely mimicking a typical appendicitis [1].

Sensitivity and specificity of computed tomography (CT) for the diagnosis of acute appendicitis is generally above 90% in most published series, and CT is now commonly performed especially in adult patients and atypical presentations. Preoperative detection of appendiceal neoplasms is important because it may result in change not only in the surgical approach (ie, laparoscopic vs open surgery) but also in the appropriate procedure (ie, appendectomy vs right hemicolectomy) [2].

Red flags on CT that help in differentiating underlying appendiceal neoplasm from appendicitis are: appendiceal diameter of >15mm, associated soft-tissue mass, wall-thickening and irregularity [3].

The majority of appendiceal masses consist of primary epithelial neoplasms, being the epithelial adenocarcinoma the most common malignant neoplasm of the appendix, with mucinous and nonmucinous histologic types occurring in 37% and 27% of cases, respectively [4].

In our case the histopathological diagnosis was nonmucinous (colonic-type) adenocarcinoma of the appendix. Characteristic imaging features of these neoplasms include a focal soft-tissue mass or subtle soft-tissue infiltration of the entire appendix, without mucocele formation. Periappendiceal fat stranding is common and may be due to extension of the primary tumour and/or superimposed appendicitis. Cross-sectional evaluation usually demonstrates direct invasion of the adjacent organs, regional and distant lymphadenopathy, and metastatic disease [2].

Right hemicolectomy is considered the standard of care, and systemic adjuvant chemotherapy is also indicated in node-positive disease [5], as happened in our case: a right hemicolectomy was eventually performed, and treatment with oxaliplatin and capecitabin was initiated.

Patients should undergo colonoscopy to evaluate for synchronous colorectal tumours. Also to assess whether the tumour displays the characteristic molecular features of hereditary nonpolyposis colorectal cancer, the expression of mismatch-repair (MMR) proteins and microsatellite instability (MSI) status must be investigated [6]. Our patient presented loss of MSH2/MSH6 expression.

Teaching points:

• Imaging findings may overlap with those of acute appendicitis.
• Features that should alert the radiologist to the presence of an underlying neoplasm are diameter of >15mm, irregular wall thickening of the appendix, enhancing soft-tissue nodularity, infiltration, or a mass.

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