The incidence of primary appendiceal cancer other than carcinoid tumor is estimated to be <0.5% of all gastrointestinal neoplasms and 0.1–0.8% of appendectomy specimens [3
]. Primary appendiceal adenocarcinoma is generally classified into two main types: cystic and colonic type. Whereas cystic-type adenocarcinoma is much more common and accounts for about two-thirds of all appendiceal tumors, colonic-type adenocarcinoma is rare [4
]. Early-stage colonic-type adenocarcinoma, such as in the current case, is quite rare. Only 32 cases, including the present case, of early colonic-type adenocarcinoma have been reported to date in the Japanese literature [7
]. The prognosis of appendiceal adenocarcinoma is said to be poor in comparison to colon cancers arising from other portions of the intestine, the overall 5-year survival rate of appendiceal adenocarcinoma being 49–64% [1
]. This is mainly because the vast majority of appendiceal adenocarcinomas is diagnosed only after disease progression. The tumor is difficult to detect at an early stage because it shows few specific symptoms or findings on examination. Most colonic-type appendiceal adenocarcinomas are discovered incidentally as a result of acute appendicitis caused by luminal obstruction associated with tumor progression. In addition, relatively rapid progression due to the anatomical features of the appendix is also partially responsible for the poor prognosis. The appendix contains abundant lymphatic tissues and a relatively thin layer, so metastasization to regional lymph nodes and/or dissemination to the peritoneal cavity is likely [1
]. Early detection is a key point to achieve improved therapeutic results of appendiceal adenocarcinoma.
It is difficult to find appendiceal tumors by routine colonoscopy, whereas some appendiceal tumors show a characteristic colonoscopy finding called ‘volcano sign’, consisting of an enlarged protruding orifice of the appendix [9
]. However, colonoscopy does not allow a qualitative diagnosis without a sufficient biopsy specimen, and therefore its diagnostic power for appendiceal tumors is still unsatisfactory. In fact, Trivedi et al. [6
] reported that preoperative biopsies showed a malignant diagnosis of only 3.1%. Meanwhile, 18
F-fluorodeoxyglucose positron emission tomography (FDG-PET) is now widely used as a new diagnostic modality. While there are some false-positive cases demonstrated by PET-CT [10
], some cases of appendiceal adenocarcinoma are preoperatively diagnosed by PET-CT [11
]. The efficacy of PET-CT for the early diagnosis of appendiceal adenocarcinoma is still controversial, but it may be a helpful diagnostic modality when used in combination with other types of examinations, such as colonoscopy.
Recurrence after surgery is significantly reduced by right hemicolectomy in comparison to appendectomy alone. The 5-year survival rate improves to 20% after appendectomy alone, and to 63% after right hemicolectomy [12
]. Therefore, the standard surgical procedure for appendiceal adenocarcinoma is right hemicolectomy with appropriate lymph node dissection, the same as for common colorectal cancers. Appendectomy is regarded as an optimal and sufficient procedure only in lesions confined to the mucosa with a negative surgical margin. Although colonoscopy and biopsy showed no apparent abnormal findings, residual atypical cells were not microscopically deniable because histopathological examination of the surgical margin of the appendix revealed atypical cells. Therefore, radical right hemicolectomy was performed in this case. Although partial resection of the cecum was a possible less invasive procedure, it is usually not a standard procedure and may cause deformity of the cecum, thus resulting in passage obstruction.
Colonoscopy in association with secondary operation is one of the essential preoperative examinations besides abdominal CT. It is also important to carefully check for the presence or absence of atypical cells around the appendiceal orifice and to rule out any other synchronous colorectal lesions because colorectal cancer is often multifocal [6
]. Long-term follow-up by colonoscopy is also recommended, especially in juvenile patients with colonic-type appendiceal adenocarcinoma, since they appear to have a higher risk to develop another colorectal cancer.
Some reports recommend limiting routine histopathological examination for surgical specimens of limited or no clinical value to reduce medical costs [13
]. However, even though gross inspection may demonstrate no tumorous lesion, there are some cases in whom histopathological examination does indeed demonstrate abnormal findings, as in the current case. Therefore, histopathological examination must always be done after not only appendectomy for acute appendicitis, but also after combined resection following another operation [15
]. Therefore, careful preoperative examination, detailed intraperitoneal inspection during surgery, and especially careful routine histopathological examinations of the excised appendix are important to detect the presence of occult appendiceal tumors.