Uncommon Presentation of Perforated Appendicitis: Abdominal Wall Abscess and Fistula Formation

Introduction

Acute appendicitis is one of the most common surgical emergencies and is the most common cause of an acute abdomen [1]. Perforation of the appendix is seen in up to 35% of cases of acute appendicitis [2]. This case is unique in that a fistula developed between the perforated appendix and the abdominal wall, resulting in an abdominal wall abscess. This report presents the case of a 45-year-old woman with a 7-day history of right lower-abdominal pain and swelling due to perforated acute appendicitis and abdominal wall abscess that required laparotomy and drainage. The current case study serves to outline the case and to highlight the challenge in diagnosing perforated appendicitis when atypical findings are present on imaging.

The incidence of acute appendicitis is about 100 cases out of every 100 000 people per year [3,4] making it a common cause of an acute abdomen. Acute appendicitis is most common during or before early adulthood, with a mean age at presentation of 28 years old [5]. Acute appendicitis is typically caused by obstruction of the appendiceal lumen, and the etiology of this obstruction tends to differ between children and adults. In children, the most common etiology of acute appendicitis is lymphoid hyperplasia, whereas the most common etiologies of acute appendicitis in adults include infection, fecaliths, and tumors [5].

Acute appendicitis is typically a clinical diagnosis, but use of various laboratory examinations and imaging can aid in diagnosis, especially when the clinical picture is not clear. White blood cell (WBC) count and C-reactive protein (CRP) are the 2 most commonly utilized laboratory tests in the diagnosis of acute appendicitis. A WBC count and CRP both within the normal range has a high negative predictive value for acute appendicitis. On the other hand, most patients with acute appendicitis have a WBC count >10 000 cells/mm3, and significantly increased WBC count >17 000 cells/mm3 in addition to elevated CRP may indicate complicated appendicitis [6]. The utilization of imaging may also aid in the diagnosis of acute appendicitis. CT scans have >95% accuracy in the diagnosis of acute appendicitis in adults, and it is thus the preferred imaging technique. Ultrasound may be efficacious in populations in which ionizing radiation risk precludes the use of CT, such as in pregnant women and children. Finally, in pregnant women with equivocal ultrasound findings, MRI may be used to aid in the diagnosis of acute appendicitis [5].

The most common complication of acute appendicitis is perforation, which can lead to abscess formation and peritonitis [5]. Complicated appendicitis is best evaluated with CT [7]. Signs of complicated appendicitis include abscess, wall enhancement defects, extraluminal air, and extraluminal appendicolith. In general, these findings have high specificity but low sensitivity [7].

Treatment options for appendicitis complicated by abscess or mass formation may include conservative medical management, percutaneous drainage with or without interval appendectomy, emergency laparoscopic, and open appendectomy. The best approach is somewhat controversial, but there is evidence that outcomes are similar across treatment modalities [8].

The current case is unique for a number of reasons. First, while perforation is a common complication of appendicitis, most appendiceal perforations result in localized peritonitis or intra-abdominal abscesses rather than externalized abscess formation [5]. In the current case, a fistulous tract formed between the perforated appendix and the abdominal wall, allowing the resultant abscess to form not locally around the appendix, but rather in the abdominal wall itself. Furthermore, given the >95% accuracy of CT scan in diagnosing appendicitis [5], the current case is also unique in that the appendix was visualized as normal on a CT scan. Finally, the case was further complicated by intra-abdominal adhesions, requiring conversion from laparoscopy to open laparotomy, further contributing to the complexity of the case. In summary, this case is unique in that the perforated appendix led to abscess formation in an uncharacteristic site while the CT scan showed no evidence of appendicitis.

Case Report

A 45-year-old woman with a pertinent past medical history of chronic pain syndrome treated with opiates, gastroesophageal reflux disease (GERD), and hysterectomy presented with a 7-day history of abdominal pain and abdominal distention. The swelling and the pain were localized to the right lower quadrant, just below the umbilicus. The pain was dull, constant, and moderate in intensity. She stated that she thought the distention was secondary to chronic constipation but remarked that a bulge inferior to the umbilicus had grown dramatically in the last 4 days. She reported subjective fevers and chills, and she denied pain radiating to the back, dysuria, hematuria, hematemesis, or hematochezia.

Physical examination in the emergency department revealed a febrile patient in mild distress secondary to pain. Vital signs revealed a temperature of 38.5°C, pulse rate 89/minute, respiratory rate 20/minute, blood pressure 118/77 mmHg, and oxygen saturation 99%. Abdominal examination revealed an atraumatic abdomen free of bruises or hernias. Swelling was noted near the umbilicus, extending to the suprapubic region, with pain on palpation.

A CT scan with IV contrast of the abdomen and pelvis showed a large, multiloculated collection consistent with an abscess in the anterior abdominal wall, with another similar abscess pocket identified in the right upper pelvis. There was no evidence of bowel obstruction, perforation, or appendicitis. Ultrasound of the pelvis showed a mixed hyperechoic and hypoechoic lesion superior to the urinary bladder, consistent with an abscess. Laboratory investigations are included in Table 1. Differential diagnoses included abdominal wall abscess, pelvic abscess, tubo-ovarian pathology, and appendicitis.

Following the repeat CT scan of the abdomen and pelvis with rectal contrast, which had shown no perforation, the decision was made to take the patient to the operating room for incision and drainage of the abdominal wall abscess and debridement of the abdominal wall. A laparoscopic approach was attempted, but the procedure was converted to a laparotomy due to adhesions. The abdominal wall abscess was drained, and fluid was collected for cultures. Following debridement of the abdominal wall, the abdominal cavity was entered.

Upon entering the abdominal cavity, the appendix was noted to be adherent to the abdominal wall. The appendix was dissected in its entirety and was sent to pathology. It was noted that the appendix had likely perforated, allowing a fistulous tract to form between the appendix and abdominal wall. Surgical photographs are included in Figure 1A and 1B. Furthermore, the pelvic abscess noted on CT scan was actually a cystic mass, which was resected and sent to pathology. Histolopathological photomicrographs of the appendix are included in Figures 2 and 3.

Following the procedure, the patient was sent to the intensive care unit (ICU). Following return to the floor, the patient returned to the OR for re-exploration of the abdominal wall and further debridement. The wound appeared to be healing and was packed prior to discharge. The diet was advanced and well tolerated, and the patient was voiding and ambulating without difficulty. She was stable and without concerns upon discharge.

Discussion

This report highlights some of the diagnostic challenges that can delay the diagnosis of appendicitis. Acute appendicitis is the most common cause of an acute abdomen requiring surgical intervention, and perforation of the appendix is seen in up to 35% of cases [1,2]. Research has shown that the finding of extraluminal abscess has a specificity of up to 100% for perforated appendicitis [2,9]. However, in this patient, fistula formation led to the development of the abscess in the abdominal wall rather than surrounding the appendix. Such a presentation on CT indeed complicates the prompt diagnosis of a perforated appendix.

In the USA, CT is used in the vast majority of appendicitis patients and has a sensitivity of 92.3% [10]. Furthermore, CT scans have been shown to outperform ultrasound, with a sensitivity of 86% in detecting appendicitis [11], and magnetic resonance imaging (MRI), which does not outperform ultrasound in detecting perforated appendicitis [12]. Unlike ultrasound, CT has the added benefit of not requiring an operator to use. However, as the current case highlights, high-sensitivity CT has limits and can mislead clinicians from acute appendicitis as the likely etiology of a patient’s presentation.

In this case, the presentation was complicated by fistula formation, making the diagnosis challenging despite advanced imaging techniques. This case underscores the need for careful clinical evaluation in patients with persistent lower-quadrant pain and abscess formation. Prior reports suggest that insidious abdominal pain with leukocytosis should raise suspicion for perforated appendicitis, even when imaging findings are inconclusive [13–15]. Similar to Lin, Tsai, and Chu, and de Souza et al, the current case report features CT imaging showing an abscess extending into the abdominal wall [14,15]. However, unlike previous reports, the current case was further complicated by an appendix that was both well-visualized and normal-appearing on CT. Furthermore, the current case is similar to prior reports in that all feature leukocytosis, which is a common presentation of appendicitis [6,13–15]. Finally, the current case utilized laparoscopy that was converted to laparotomy. Previous case reports typically utilize open appendectomy, which was utilized in the current case report. However, some evidence suggests that outcomes are similar in patients with complicated appendicitis who undergo conservative medical management, percutaneous drainage with or without interval appendectomy, or emergency laparoscopic or open appendectomy [8].

Conclusions

The current case highlights the potential difficulty in identifying perforated appendicitis prior to surgery. There should be a high degree of clinical suspicion for perforated appendicitis in the context of an abdominal wall abscess, leukocytosis, and right lower-quadrant pain. Prompt surgical intervention is critical, even in cases where imaging does not initially reveal clear signs of appendicitis.