A 34-Year-Old Man With a Traumatic Penetrating Injury of the Buttock and Occult Retained Foreign Body Resulting in a High Anal Fistula Managed by Trans-Sphincteric Surgery

Introduction

Penetrating buttock injury is a rare clinical trauma that poses a major challenge to surgeons and can be life-threatening in severe cases [1]. Under normal circumstances, patients with unstable hemodynamics need immediate surgical treatment, while patients with stable hemodynamics need detailed medical history-taking, comprehensive wound assessment, and preoperative selection of appropriate examination methods according to the nature of foreign bodies in time to identify the presence of occult foreign bodies, to avoid intraoperative damage to important blood vessels and organs [2].

Penetrating buttock injury is a rare yet clinically significant trauma that can be life-threatening in severe cases, primarily due to potential damage to vascular and neural structures [3]. Management is determined chiefly by hemodynamic stability: unstable patients require immediate surgical intervention, whereas stable patients should undergo a comprehensive evaluation including detailed history, physical examination, and targeted imaging (eg, CT or MRI) to detect radiolucent foreign bodies and delineate anatomical relationships [4]. Preoperative planning is critical to avoid iatrogenic injury during exploration. Available surgical approaches for removing occult foreign bodies include the transanal approach, which is suitable for objects near the rectal wall and avoids external sphincter disruption, but offers limited exposure and carries a risk of fecal contamination; the transgluteal approach, which allows direct access to objects within gluteal muscles, but poses risks of injury to the sphincter complex, sciatic nerve, and pudendal vessels; and the intersphincteric approach, which uses the plane between the internal and external sphincters and is particularly advantageous for foreign bodies associated with high anal fistulas due to its ability to minimize sphincter damage and reduce the risk of postoperative incontinence [5]. The choice of technique should be guided by precise imaging and a thorough understanding of pelvic anatomy to ensure complete foreign body removal while preserving functional integrity [6].

Penetrating trauma, including penetrating injury to the buttock, can lead to a series of severe consequences and complications. According to Marietta and Burns, penetrating trauma often causes direct tissue destruction and blood loss, and high-velocity injuries can induce shock waves and secondary cavitation, resulting in distant tissue damage, necrosis, and bleeding [7]. For penetrating buttock injury specifically, Lunevicius et al noted that it is prone to involving deep pelvic structures, with common complications including vascular injury (eg, damage to pudendal vessels), neural injury (especially sciatic nerve injury leading to lower-limb sensory and motor dysfunction), and urogenital tract injury [8]. Fallon et al further emphasized that occult foreign body residue after penetrating buttock injury is likely to cause delayed infection, manifesting as perianal abscess, cellulitis, and eventually progressing to anal fistula [9], as seen in this case. Additionally, penetrating trauma can lead to systemic complications such as hemorrhagic shock, sepsis, and disseminated intravascular coagulation, while local complications include hematoma formation, wound dehiscence, and pseudoaneurysm [7]. These consequences and complications highlight the need for comprehensive evaluation and timely intervention for patients with penetrating buttock injury.

Peri-levator high anal fistulas, as defined by Garg [10] et al include 5 subtypes: suprasphincteric, extrasphincteric, supralevator, high outer sphincteric, and high intrarectal. For the management of these subtypes, Tarasconi et al emphasized that the core principles include sphincter preservation (to avoid fecal incontinence) and complete fistula tract excision/drainage. Specific strategies vary by subtype. For suprasphincteric and high outer-sphincteric fistulas, intersphincteric or trans-sphincteric approaches are preferred, with seton placement to promote gradual healing and reduce sphincter damage. For supralevator fistulas, combine imaging-guided drainage (eg, CT or ultrasound-guided aspiration) with staged surgery to address deep pelvic collections before fistula repair. Extrasphincteric fistulas require extensive pelvic exploration, often with rectal wall repair and omental flap coverage for complex cases. High intrarectal fistulas are managed with transanal endoscopic surgery (TES) for direct access to rectal lumen openings, combined with antibiotic irrigation to control infection [11].

Previous similar case reports have documented foreign body-induced anal fistulas after penetrating buttock injury. Blue et al [5] reported the case of a 45-year-old man who developed recurrent perianal abscess and extrasphincteric fistula 6 months after gluteal wooden splinter injury, with the foreign body initially missed on imaging, treated via transgluteal removal. Long et al [2] described the case of a 32-year-old man with high anal fistula from a retained metal fragment, managed by spinal endoscopy for foreign body extraction, without postoperative fecal incontinence. Kocierz et al [14] reported a low trans-sphincteric fistula due to retained wire, cured by simple perianal incision.

This report describes the case of a 34-year-old man with a traumatic penetrating injury of the buttock and occult retained foreign body resulting in a high anal fistula managed with trans-sphincteric surgery.

Case Report

On May 1, 2022, a 34-year-old male self-employed worker fell from a height while climbing over a wall during the COVID-19 lockdown, and a branch accidentally inserted into the buttock. The patient pulled out the branch by himself and went to the Emergency Department (ED) of a nearby medical center for treatment. The ED doctor found no abnormality on X-ray, and treated the patient with “buttock debridement and suture” as an aseptic trauma. However, 6 days later, the patient developed perianal swelling and pain, accompanied by discharge of pus, lower-abdominal pain, and recurrent fever. He returned to the center and went to the Anorectal Department for treatment. Routine blood tests at admission showed a white blood cell count 20.93×109/L, neutrophils 82.1%, C-reactive protein 216.45 g/L, alanine aminotransferase 94.0 U/L, and creatinine 134.0 umol/L. CT of the anus showed swelling of the left pelvic wall with surrounding air accumulation, diagnosed as diffuse cellulitis of the left pelvic and lower abdominal wall, pelvico-rectal abscess, and acute hepatorenal syndrome. At this time, low-density air shadows of the left pelvic wall could be seen on CT, but were not noticed by the Imaging Department and Proctology Department (Figure 1). Two days after hospital admission, he underwent incision and drainage of a peri-pelvico-rectal abscess under lumbar anesthesia. A pelvic MRI plain scan and enhanced re-examination on the second day after surgery showed, after drainage of the pelvico-rectal abscess, there was contusion and laceration of the left obturator muscle with hematoma, contusion of iliac muscle and submuscular muscle, and diffuse cellulitis in the left pelvic cavity and the anterior lower abdominal wall extraperitoneal space. On the 4th day after surgery, routine blood testing and C-reactive protein showed a white blood cell count 19.86 × 109/L, neutrophil 83.3%, and C-reactive protein 43.64 mg/L. According to previous experience of abscess incision and drainage, after abscess incision and drainage, postoperative inflammation normally decreases significantly, but our patient’s inflammatory markers showed no significant improvement on re-examination, but the clinicians did not assess this. After repeated drainage tube irrigation, the infection was barely controlled, and the wound did not heal for a long time.

On May 12, 2023, due to further aggravation of anal swelling and pain, the patient went to the Anorectal Department of another medical center for treatment. After admission, CT examination showed hypodermic low-density shadow of left iliopsoas muscle, obturator internus muscle, perianal peri-anus muscle, considering inflammatory lesions involving the left lateral wall of the bladder, left levator ani muscle, and obturator internus muscle. At this time, the occult foreign body on CT had been strengthened, but the Imaging Department and anorectal doctors were still unaware of it. The patient was diagnosed and treated as having a perianal abscess, perianal abscess incision and drainage was performed on the second day of admission, and the patient was treated with anti-infection and drainage tube irrigation after surgery. After 3 weeks of treatment, the symptoms were improved and he was discharged (Figure 2). However, 2 months after discharge, he was admitted to the hospital a second time due to insufficient wound healing. He was diagnosed with a high anal fistula and underwent a high anal fistula incision and hanging operation, but the wound did not heal after surgery.

On November 13, 2023, he went to the Anorectal Department of our center for further treatment, reporting repeated perianal swelling, pain, pus discharge, and occasional involuntary fecal discharge. After admission, MRI plain scan and enhancement in the anal area showed an abscess cavity of the left ischo-rectal fossa with low signal spot in the central area and residual foreign body (Figure 3). A specialist examination found old surgical scars about 3 cm, 4 cm, and 6 cm in length on the left buttock near the anus. An open wound was found at the left rear of the anus 2 cm away from the anal margin, and there was a discharge of thick yellow pus when squeezed. Digital examination revealed a foreign body felt under the left rectal mucosa, and the anal sphincter was relaxed. He was diagnosed as having a high anal fistula, foreign bodies in the buttocks, incomplete fecal contrast-enhanced shadow of foreign body in sagittal plane of CT incontinence, and a high anal fistula incision, drainage and catheterization combined with removal of foreign body in buttocks through sphincter and anal debridement was performed on the 4th day after admission. Five bramble foreign bodies (Figure 4) were removed during the operation, and the catheterization depth reached 11 cm, with no residual foreign bodies. After the operation, anti-infection and metronidazole solution drainage tube irrigation were given, the drainage tube was removed 1 month after the operation, and the wound was completely healed 2 months after the operation (Figure 5), and no recurrence was observed at 6-month follow-up. During follow-up, key parameters assessed included wound healing, symptom resolution (pain, swelling, discharge), and anal functional recovery – particularly improvement in preoperative episodes of liquid stool incontinence. Postoperatively, the patient reported complete resolution of involuntary leakage, supported by improved sphincter tone on digital examination.

Discussion

This case report offers 3 key lessons for clinical practice. (1) Clinicians should take a detailed traumatic history for patients with perianal symptoms to rule out occult foreign body residue from prior penetrating injuries. (2) Multi-modal imaging (especially MRI) is critical for detecting deep-seated, radiolucent foreign bodies and accurately classifying high anal fistulas. (3) Selecting appropriate sphincter-sparing surgical approaches (eg, trans-sphincteric surgery) is essential to balance complete foreign body removal and preservation of anal function in such cases.

Penetrating injury can be divided into 2 categories: one is the body injury caused by the body hitting the stationary object, and the other is the penetrating injury caused by the moving object penetrating the stationary object [12]. Our patient had an injury caused by his body hitting a stationary object. Penetrating injury is mostly caused by foreign body trauma – penetrating injury in European and North American countries is mostly caused by violent crimes such as gunshot wounds or metal knife wounds, while penetrating injury caused by car accidents, industrial injuries, or accidental falls is more common in Asia [3]. No matter what the cause, the physical damage caused by penetration injury can be fatal, and saving the life of the injured through clinical treatment or intervention is often difficult [1]. Penetrating buttock injury has the risk of damaging the rectum, the vascular system, sciatic nerve, and urogenital tract, and can be divided into 4 quadrants according to the buttock injury quadrant – upper outer, lower outer, lower inner and upper inner – of which the lower inner quadrant entrance wound is most likely to be combined with rectal injury. Research has shown that determining the injury quadrant helps to identify those patients who are most at risk of rectal and urethral injury early in the visit. However, damage quadrants are not helpful in predicting vascular or nerve damage. For patients with penetrating buttock injury, CT should be performed in all patients after initial examination and resuscitation to assess the risk of rectal, vascular, and nerve damage. About 80% of rectal injuries are secondary to penetrating injuries, and suspected rectal injuries must be evaluated by anal digital examination, proctoscopy, or CT scan if the patient’s hemodynamic status permits. The results of digital rectal examination include rectal bleeding, rectal wall defects, and decreased anal sphincter tone, with sensitivity of 33% to 52% and a false-positive rate of 63% to 67%. CT examination shows wound trace extending near the rectum, intestinal wall defect, extravasation of contrast agent in the cavity, or free gas outside the rectal cavity. Proctoscopy is highly sensitive in evaluating rectal injury, and inadequate bowel preparation and related injury are important reasons for the lower sensitivity of proctoscopy [4,6,13]. Due to the uncertainty of the injury site in penetrating buttock injury, the complex anatomical structure of the injured area, and the absence of a clear surgical incision before surgery, it is often necessary to expose the penetrating object and wound passage to the maximum extent during the operation, and simply removing the penetrating object often results in residual foreign bodies [2]. In this case, the penetrating object was not found in the early stage, resulting in foreign body residue, and perianal abscess was secondary after debridement and suturing, which eventually evolved into a high anal fistula. Several similar case reports have been published, which can be compared with the current case. Blue et al [5] reported a 45-year-old male who developed recurrent perianal abscess and extrasphincteric anal fistula 6 months after a gluteal wooden splinter injury; the foreign body was initially missed on imaging, and the patient underwent transgluteal foreign body removal with 3-month postoperative healing. Compared to our case, this patient had a shorter diagnosis delay (6 months vs 18 months), a different fistula subtype (extrasphincteric vs suprasphincteric), a more invasive surgical approach (transgluteal vs sphincter-sparing trans-sphincteric), and a longer healing time (3 months vs 2 months). Long ZS et al [2] described a 32-year-old male with a high anal fistula due to a retained metal fragment from buttock penetrating trauma; spinal endoscopy was used for foreign body localization and removal, with no postoperative fecal incontinence. Unlike our patient – who had preoperative fecal incontinence, was diagnosed via MRI, and underwent open trans-sphincteric surgery – this case had no incontinence, relied on endoscopy for diagnosis, and adopted a minimally invasive approach. Kocierz L et al [14]reported a patient with perianal fistula (low trans-sphincteric type) caused by a retained wire after buttock injury, which was cured by simple perianal incision for foreign body extraction. Our case differed in fistula severity (high vs low subtype) and required complex sphincter-sparing surgery, while this case only needed a simple incision.

In penetrating injuries, deep foreign bodies are often difficult to identify, such as repeated non-healing of the wound, the possibility of foreign body residue should be considered. There is a lack of literature to discuss the location of deep foreign bodies in the buttocks and the best way to remove them. Relevant literature reports that visualization techniques such as cystoscopy and spinal endoscopy have been successful in removing residual foreign bodies in the buttocks [2,5]. Most superficial foreign bodies can be easily detected through careful wound exploration and physical examination, but some deep foreign bodies are difficult to explore and find through clinical examination alone. Plain X-ray film can easily detect radio-impenetrable foreign bodies, such as metal, but radiography technology has low sensitivity in detecting radio-impenetrable foreign bodies, such as wood or plastic. CT examination is the gold standard for radio-impenetrable foreign body imaging [15]. Compared with traditional X-ray, CT examination not only improves the detectability of foreign bodies, but also improves the detection of foreign bodies. It can also accurately locate foreign bodies, which is very important for the exclusion of vital organ injury and the formulation of surgical plans. Studies have shown that the utility of CT varies with the time after injury. In the acute stage, CT shows wood as a low-density air shadow, which is easy to misdiagnose, especially small wood pieces. In the subacute stage, wood absorbs moisture and appears as a medium-density shadow similar to fat on CT. In the

chronic stage, the wood gradually showed a high-density shadow and was easy to identify [16]. Ultrasonography has unique advantages in detecting foreign bodies in superficial tissues, and its resolution is even higher than that of CT or MRI. MRI is superior to ultrasound evaluation in detecting foreign bodies that can be penetrated by radiation, especially those with small diameters. In addition, foreign bodies are more easily identified on MRI when they are encased in fluid or abscesses[17]. For radio-penetrable foreign bodies, MRI may be the only way to detect foreign bodies undetectable on X-rays, CT, and ultrasound [15]. In penetrating wounds, organic materials such as wood are more conducive to microbial growth than metallic materials, and are highly susceptible to infection and inflammation [18]. The foreign bodies in our patient were wood, but the ED doctor did not perform X-ray examination. Foreign body residue is an important reason leading to the development of the disease. Early CT examination of the foreign bodies showed low-density shadows like air, which is not easy to detect, and is a common cause of delayed diagnosis. In the later stage, foreign bodies showed high-density shadows in CT examination after absorbing water, which was relatively easy to identify. Studies have shown that MRI is can detect foreign bodies when other examination methods cannot [15]. In the later MRI examination of this patient, the foreign bodies were found to be low-density shadows with surrounding cystic lesions, which was in sharp contrast to the local inflammatory tissue of the surrounding high-density shadow.

Residual foreign bodies are a very unusual cause of anal fistulas. Incision, drainage, and removal of foreign bodies are key to pain relief and healing [14]. Surgical approaches for this patient were transanal skin approach, trans-anorectal approach, and trans-anal-inter-sphincter approach. Through the perianal skin approach, the external anal sphincter needs to be cut during the operation, which easily damages the sphincter and makes it difficult to find and remove foreign bodies. The transanal approach is prone to bleeding during incision of the rectum wall, and the operative field is not good, which also makes it difficult to find and remove foreign bodies. Our patient had incomplete fecal incontinence before surgery, and protection of the sphincter was the key to selecting the surgical method. Therefore, the transanal sphincter gap approach was the most suitable surgical approach, as it could reduce anal sphincter damage and facilitate recovery of anal function after surgery.

Conclusions

For this type of high anal fistula caused by long-term retention of occult foreign bodies, attention should be paid to 7 aspects during diagnosis and treatment: (1) A detailed medical history should be obtained. (2) A careful and comprehensive physical examination – especially digital rectal examination and endoscopic rectal examination – should be conducted. (3) Relevant auxiliary examinations may be needed, and pelvic MRI has advantages over other auxiliary examinations for patients with a long disease course and deep, hard-to-locate foreign bodies. (4) Careful surgery is essential, with foreign body removal as the key, and the correct surgical method should be selected to avoid anal sphincter injury caused by rough manipulation. (5) Multidisciplinary diagnosis and treatment are important, and multidisciplinary cooperation can make up for the blind spots of specialist knowledge and the limitations of treatment methods. (6) If a patient has a trauma history and the wound repeatedly fails to heal after debridement and antibiotic treatment, the possibility of residual foreign bodies in the tissue should be considered. (7) Meticulous postoperative care should be provided, with long-term dressing changes continued until the surgical incision heals.