A Delayed Postoperative Anastomotic Submucosal Abscess

ABSTRACT

Delayed anastomotic submucosal abscess is a rare complication of rectal tumor resection. A submucosal tumor-like lesion near the anastomotic site was detected in a 57-year-old woman, and pus and sutures were found through spontaneously formed fistulas. Endoscopic ultrasound confirmed the presence of hyperechoic pus flowing out from the fistulas on compression of the lesion. The patient recovered well without surgery. This case indicates that submucosal abscess should be taken into consideration if suspected submucosal tumor-like lesions are detected after rectal surgery. Endoscopic drainage combined with antibiotic treatment may be an effective strategy for limited postoperative anastomotic abscess.

INTRODUCTION

Delayed anastomotic submucosal abscess is a rare complication following rectal tumor resection. Common therapeutic strategies include percutaneous drainage and endoscopic ultrasound (EUS)-guided drainage. We report a case of a 57-year-old woman who developed a delayed anastomotic submucosal abscess. She achieved satisfactory recovery after the spontaneous formation of a fistula and subsequent pus drainage, followed by antimicrobial therapy, thereby eliminating the necessity for surgical intervention.

CASE REPORT

A 57-year-old woman presented with lower abdominal pain for 2 days, and pelvic computed tomography at a local hospital revealed intestinal obstruction and thickening of the anastomotic wall (Figure 1). After 1 week of conservative treatment, she was referred to our hospital for further evaluation. Eight years ago, the patient underwent radical resection of a rectal neuroendocrine tumor and had not been consistent with follow-up visits. She had no significant personal or family medical history and displayed no positive signs on physical examination. Laboratory tests, including C-reactive protein and leukocyte count, showed no abnormalities. Colonoscopy at our hospital identified a protuberance near the anastomotic site, positioned 5 cm from the anus and measuring approximately 3 × 4 cm (Figure 1). Two fistulas were observed, displaying pus and sutures after flushing with water (Figure 1). Subsequent EUS revealed a mixed hypoechoic and hyperechoic structure measuring about 3.63 × 1.26 cm in the rectal wall (Figure 1). Compression of the lesion resulted in drainage of hyperechoic pus from the fistula, as depicted in the animation (Video 1). Based on the medical history, imaging, and endoscopic findings, the patient was diagnosed with a delayed anastomotic submucosal abscess with fistulas. Conservative anti-infective treatment with ceftriaxone (2 g per day, 2 weeks) was initiated, along with a low residue diet, probiotics, and glutamine enteric capsules, as the patient refused surgery. A follow-up examination after 1 month showed no recurrence during white light endoscopy (Figure 1).

Figure 1.

(A) Pelvic computed tomography initially revealed intestinal obstruction and thickening of the anastomotic wall (arrowhead). (B) Colonoscopy identified a submucosal tumor-like lesion near the anastomotic site (arrowhead). (C) Fistulas were observed on the lesion, accompanied by visible pus (black arrowhead) and sutures (white arrowhead). (D) Endoscopic ultrasound revealed a mixed hypoechoic and hyperechoic structure in the rectal wall (arrowhead). (E) Repeat colonoscopy showed no re-emergence of the previously observed lesion.

Video 1 Endoscopic ultrasound shows pus flowing out of the lesion

DISCUSSION

This case report highlights a delayed anastomotic submucosal abscess occurred 8 years after rectal neuroendocrine tumor surgery, a rare complication following rectal tumor resection. Patients with rectal anastomotic abscesses typically present with nonspecific symptoms such as anal distension and lower abdominal pain, and their inflammatory indicator levels in blood tests are often normal, complicating the differential diagnosis. Anastomotic submucosal abscess usually presents imaging and EUS findings resembling submucosal tumors, with preoperative diagnoses potentially including gastrointestinal stromal tumors, neuroendocrine tumors, or rectal cancer.¹ In this case, pelvic computed tomography initially suggested the presence of a tumor, while colonoscopy revealed a submucosal mass; however, findings of fistulas and pus discharge during EUS aided the diagnostic process. Abdominopelvic abscesses greater than 3 cm usually require drainage, and most abscesses are amenable to percutaneous drainage. In some cases, percutaneous drainage is not recommended due to limitations such as the absence of a safe radiological window for puncture or the patient's esthetic preferences. In such circumstances, EUS-guided drainage is an appropriate choice.² Though for abdominopelvic abscesses, drainage combined with antibiotics is a safe and effective treatment strategy, and guidelines for abscess in the intestinal tract wall are lacking.³ Previous report has demonstrated successful outcomes with endoscopic fenestration and antibiotic therapy.⁴ However, no case of abscess limited in rectal wall with spontaneous sinus drainage has been reported. In the current case, spontaneous fistula formation and pus drainage, followed by antimicrobial therapy, led to symptom relief and lesion resolution, supporting the feasibility of drainage with anti-infective treatment for limited postoperative anastomotic abscesses.

In conclusion, delayed postoperative anastomotic submucosal abscess is a rare condition, and successful conservative treatment following spontaneous drainage has not been extensively reported. Clinicians should consider anastomotic submucosal abscess in the differential diagnosis of patients after rectal surgery if suspicious submucosal tumors are found during late postoperative follow-up. Endoscopic drainage combined with antibiotic therapy may be a safe and effective strategy for managing limited postoperative anastomotic abscesses after rectal surgery.

DISCLOSURES

Author contributions: Writing-original draft: X-T Hu. Data and image curation: X-T Hu and D. Wang. Treatment of the patient was conducted by D. Wang. All authors reviewed the draft manuscript and critically revised it for intellectual content. All authors have approved the final version of the manuscript for publication. D. Wang is the article guarantor.

Financial disclosure: None to report.

Informed consent was obtained for this case report.