Colon cancer is a common malignant tumor; in recent years, many evidence-based medical treatment methods from multiple disciplines have significantly improved the survival rate and quality of life of colon cancer patients; and the medical and surgical treatment of colon cancer has become increasingly standardized (1). However, due to individual differences and other reasons, some patients often have complications such as perforation, bleeding, obstruction and abscess formation, which leads to these patients not being able to immediately undergo standardized treatment in accordance with the guidelines (2). Therefore, how to deal with these complications in a timely and effective manner and get the patient’s tumor treatment to return to the standardized treatment has an important impact on the prognosis of patients. In this article, we present an analysis of a very rare complication of colon cancer, retroperitoneal abscess.

The colon is an interperitoneal organ, and the ascending and descending colons are located behind the peritoneum (3). Tumors in these two places will cause retroperitoneal abscesses due to tumor invasion and perforation. We found that retroperitoneal abscess due to colon cancer has only been reported via case reports and is a rare condition with an incidence of 0.3%, according to some literature reports (4). Through these reports, it is clear that due to the lack of treatment experience available for reference, there are enormous differences in the treatment methods and treatment outcomes of such patients, and many of these cases are misdiagnosed. Therefore, there are many challenges for clinicians regarding how to deal with such patients accurately, effectively and in a timely manner. Based on this, we retrospectively compared and analyzed the basic characteristics, clinical symptoms, laboratory tests, imaging examinations, treatment methods and prognosis of 4 patients in our hospital and 57 patients reported in the literature. Through these comparative analyses, this paper attempts to provide an optimal reference for the diagnosis and treatment of retroperitoneal abscess associated with colon cancer.

We extracted 1013 colon cancer patients admitted to our hospital from October 2017 to October 2022, and the first two doctors searched for colon cancer cases associated with abscess through CT and MRI imaging information systems. The search range included descriptive texts of the imaging results and diagnostic conclusions. Next, the patients who were initially screened were manually queried through the clinical information system to confirm whether the patient had a retroperitoneal abscess, and for the final confirmed patients, detailed clinical information, including the basic information of the patient, tumor location, abscess location, scope, symptoms, physical examination, microorganisms, imaging tests, treatment methods, etc., were recored. Follow-up of the patients was done by one doctor. Literature reading and information extraction were completed by 3 doctors. The scope of of search included PubMed, EMBASE and Web of Science, updated on February 10, 2023, and was first completed by 3 doctors alone. The extracted information included basic information on the patients, tumor location, abscess location, scope, symptoms, physical examination, microorganisms, imaging tests, treatment methods. Finally, all authors complemented and verified the collected data. In order to effectively demonstrate the characteristics of patients with retroperitoneal abscess caused by colon cancer, we conducted a comprehensive analysis in five major aspects, including patient characteristics, clinical symptoms, laboratory examinations, imaging studies, and treatment. At the beginning of each aspect, we first analyzed the characteristics of patients from our institution, and then provided detailed descriptions based on the extracted cases from the literature.

Retroperitoneal abscess is a rare complication in colorectal cancer patients, and the specific incidence is unclear. Our hospital probability of occurrence is approximately 0.39%, which is consistent with the 0.3% reported in other studies (4, 7). Due to the low incidence, to date, reports of colorectal cancer associated with retroperitoneal abscess have only been reported in case report literature, and to our knowledge, this is the first comprehensive analysis of the largest dataset of colorectal cancer associated with retroperitoneal abscess. Through the analysis of 61 patients, we found that colon cancer associated with retroperitoneal abscess often occurred in elderly patients aged > 60 years, with slightly more men than women; and the occurrence of the disease did not vary regionally; and the disease was reported worldwide. Right colon cancer, particularly malignancy tumors in the ileocecal region, is the most common location for this clinical sign. However, considering that the incidence of left colon cancer is generally lower than that of right colon cancer (54), the overall incidence of left colon cancer associated with retroperitoneal abscess is not lower than that of right colon cancer. Pathologically, almost all these patients have advanced colorectal adenocarcinoma.

Clinically, patients with colon cancer are admitted to hospitals frequently with hematochezia, abdominal pain, and the changes in defecation habits (55), whereas patients with retroperitoneal abscesses often have masked and atypical symptoms, and gastrointestinal symptoms are often absent. Because retroperitoneal symptoms are not as pronounced as those of intraperitoneal perforation, in this study, we found that some patients had insidious symptoms of fever and weight loss in the early stage, and these patients often do not choose to seek medical attention because the symptoms are atypical. Most patients were admitted to hospitals with corresponding discomfort due to retroperitoneal abscess or iliopsoas abscess, most notably pain and swelling in the thighs, abdomen, and lower back. The misdiagnosis rate of this disease is high. Of the 4 patients received by our department, three patients were misdiagnosed at their initial visit at local hospital, while the misdiagnosis rate of the cases extracted from the literature was 43.9%. The reasons for the misdiagnose are manifold, with two directions being the core causes. First, due to the lack of digestive system symptoms, patients often seek medical advice due to pain, which leads to errors in the initial visit and a lack of a systematic examination. Second, there are various causes of retroperitoneal abscess or iliopsoas muscle abscess, such as tuberculosis of the spine, Crohn’s disease, appendicitis, diverticulitis, urinary tract infection, and cancer (56, 57). Diseases of the digestive system are not the core cause, and some patients often receive emergency admission (58, 59). Therefore, in these patients, the main focus is on treating their abscess and subcutaneous necrotic diseases, while ignoring the primary disease after admission. In addition, early diagnosis of retroperitoneal abscess is sometimes difficult because the retroperitoneal space is relatively invisible to the examiner. When an abscess forms within the abdominal cavity, the patient can often quickly feel infection due to the sensitivity of the peritoneum, and symptoms of peritoneal irritation, such as tenderness and muscle tension, can be exhibited. When the abscess forms only in the retroperitoneal location, the symptoms are mild and atypical. Therefore, in clinical practice, systematic thinking and the exclusion of diagnoses should be performed for patients with retroperitoneal abscess, and a discussion within an MDT is particularly important. Misdiagnosis not only delays the treatment of patients, but also affects their prognosis due to tumor progression.

The most obvious laboratory indicator in patients with colorectal cancer and retroperitoneal abscess is an increase in inflammation related indicators, including white blood cells, CRP, and procalcitonin. Anemia is another important characteristic, that may be related to tumor necrosis and bleeding, repeated inflammatory stimulation, and body consumption. In this article, we found that colorectal and retroperitoneal abscesses did not occur suddenly. Hidden symptoms such as fever and weight loss often persist for a long time, and substances such as fecal fluid are often not detected in the abscess drainage fluid. These findings suggest that retroperitoneal abscess caused by colorectal cancer may be caused by the translocation of intestinal flora to the retroperitoneum through small perforations caused by tumor necrosis and damaged intestinal barriers. The bacterial culture of pus confirmed that the bacterial population was mainly Escherichia coli from the intestine. It is worth noting that more than 50% of patients have elevated tumor markers for CEA and CA199, indicating that these patients are mostly diagnosed with mid- to late-stage tumors. When the etiology of retroperitoneal abscess is difficult to diagnose, elevated tumor markers can be an important reference indicator for the origin of colorectal cancer.

Compared to clinical symptoms and laboratory examinations, imaging methods such as CT, MRI, ultrasound, and X-ray imaging are the core examination methods for colorectal cancer associated with retroperitoneal abscess. In this paper, based on the results of the CT examinations, we found that patients with retroperitoneal abscess due to colorectal cancer often have abscesses with a large range of sizes, which can compress tissue., resulting in intestinal masses that are not easy to find, and this is also an important cause of misdiagnose in patients. Through the CT analysis of large datasets and the imaging description of the posterior peritoneum by A. Coffin et al. (3), we statistically found that the main distribution areas of retroperitoneal abscess caused by colon cancer were the pararenal posterior space and the posterior iliopsoas muscle retroperitoneal chamber, and the pararenal anterior space and the perirenal space were affected in only one patient. Retroperitoneal abscesses due to colon cancer are mainly presented iliopsoas muscles (100% of our case and 87.2% of the cases in the literature). The psoas major muscle extends from T12 to the trochanter, which may be affected by gravity, and most of the abscess flows down the psoas major muscle, resulting in a local abscess of the iliopsoas muscle, the thigh adductor group and subcutaneous tissue around the end of the psoas muscle. In addition, drainage of the abscess through the anatomical weakness of the lumbar hernia to the upper buttocks and subcutaneous tissue of the lumbar spine is another important method, and it is worth noting that right colon cancer is more likely to cause subcutaneous abscesses due to anatomical factors. There is a certain difference between peritoneal abscesses formed by colorectal cancer and other peritoneal abscesses, abscesses formed by colon cancer often take a certain amount of time to develop, while retroperitoneal abscesses caused by diverticula are often suddenly, with their retroperitoneal diffusion being wider (60).

Currently, the treatment methods for retroperitoneal abscess caused by colorectal cancer vary, and different treatment methods will lead to completely different treatment outcomes for such patients. Here, case reports and our cases are combined for illustration, and the best treatment methods for such patients are discussed. The first treatment method, simple incision and drainage plus anti-inflammatory treatment, can improve the symptoms of the abscess in a short time, but because the primary disease is not treated, the patient may experience repeated symptoms, enterocutaneous fistula formation, skin damage, multiple hospitalizations, and surgery. However, drainage can create opportunities for subsequent surgery. Through drainage, many abscess symptoms disappeared. At this time, a clear diagnosis can be made and surgical treatment can be performed. The second way is for the tumor to invade the posterior peritoneum, with or without microabscesses. If only medical treatment of the tumor is carried out first, it can lead to abscess formation, abscess spread, increased infection, limited limb activity, and necrotizing fasciitis. The third method is direct colon resection and intraopertive (41) debridement and drainage. However, due to the presence of an abscess, incision of the posterior peritoneum may cause the abscess to spread to the abdominal cavity, tumor resection may not be complete, and the patient may not be able to tolerate surgery. In our cases, two patients underwent direct surgical treatment. Although one patient survived after 2 years of follow-up, the surgical wound was large, and the surgery was difficult, and may required multidisciplinary cooperation. The fourth method involves comprehensive treatment such as anti-inflammatory and abscess drainage, proximal enterostomy, radiotherapy and chemotherapy, plus radical surgery and ostomy, as well as postoperative comprehensive treatment. This method takes a long time, but it can achieve radical resection. Several scholars have reported this scheme with obvious results (37, 41, 48). In our case series, this method was adopted for tow patients, and the current treatment effect is good. Although the drainage time of patients undergoing direct surgery is significantly shortened, and some patients can achieve long-term survival, according to literature reports, direct extended surgery is also an important cause of death. The specific reason may be that patients cannot tolerate large-scale surgery, and intestinal anastomosis is not encouraged during surgery, which may lead not only to anastomotic leakage, but also to patient death. It is worth noting that if comprehensive treatment is performed, it is necessary to obtain specimens for pathological examination and genetic testing before surgery. In the case of abscess, it is sometimes difficult to obtain tumor tissue through colonoscopy, and colonoscopy is performed from the stoma end after stoma. CT and ultrasound guided localization can be used as better alternatives. The author does not recommend performing laparotomy and endoscopic biopsy, which not only easily leads to pus contamination of the abdominal cavity, but also leads to tumor dissemination in the abdominal cavity.

In summary, colon cancer combined with retroperitoneal abscess often has hidden symptoms of fever and weight loss. The clinical manifestations are mainly pain in the thigh, abdomen, and back caused by an iliopsoas muscle abscess. When patients have these symptoms, they need to undergo systematic evaluation, tumor markers testings, CT, and other examinations to rule out the possibility of colon cancer. Clear and timely diagnosis is the core of treatment for such patients. In terms of treatment, anti-inflammatory agents and abscess drainage are the primary treatment items. Proximal enterostomy can not only alleviate inflammation and abscesses, but also create conditions for comprehensive treatment. After comprehensive treatment, selecting the opportunity to perform radical tumor surgery and stoma reduction surgery may be the best treatment plan.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding authors.

This study has been approved by Ethical Approval for Clinical Research Projects under Medical Ethics Committee, Zhongnan Hospital of Wuhan University (2021061). The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was not required from the participants or the participants’ legal guardians/next of kin in accordance with the national legislation and institutional requirements. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

DL and HY conceived and designed the study. JZ and SW performed the experiments and the statistical analysis. JZ, CL, QQ and ZD participated in the discussion and interpretation of the data. DL and JZ wrote the manuscript. DL and JZ read the literature. CL, QQ and ZD performed surgical treatment. DL and HY confirmed the authenticity of all the raw data. All authors contributed to the article and approved the submitted version.