The most common presenting symptoms and signs in patients with internal penetrating disease include abdominal pain (84%), fever (49%), nausea and vomiting (41%), diarrhea (25%), and presence of a fistula (14%) [2]. There may also be features of partial bowel obstruction, including a colicky nature of the pain, vomiting, abdominal distention, and/or intermittent constipation [3]. Additional symptoms may be present depending on the nature and location of the abscess. The right lower quadrant is the most common location of abscess, followed by the pelvis [4]. If an abscess is adjacent to the bladder, a patient may have urinary symptoms, while local irritation of the psoas muscle from an abscess in the distal ileal region can present as refusal to walk or bear weight [2].

Physical examination may demonstrate localized tenderness and an abdominal mass may be palpable. Peritoneal signs such as rebound tenderness and involuntary guarding may also be present. Abscess in the right lower quadrant secondary to ileal disease can be difficult to distinguish from acute appendicitis on physical examination. Pelvic abscess may be palpable as a tender bulge on rectal exam. In a patient with known CD, development of intra-abdominal abscess may also be coupled with other signs of active disease, such as poor growth or weight loss, extraintestinal manifestations including oral ulcers or arthritis, or perianal findings such as tags or fistulae [2].

Laboratory evaluation will not be specific for an intra-abdominal process, but there may be abnormalities in complete blood count (leukocytosis, anemia, thrombocytosis), complete metabolic panel (electrolyte disturbances, hypoalbuminemia), and elevation of C-reactive protein and/or erythrocyte sedimentation rate. It can be useful to compare these values to previous results to establish a trend or deterioration from a patient’s baseline. In patients with abdominal pain and vomiting, liver and pancreatic enzymes should be investigated, and urinalysis and urine culture should be obtained in any patient with urinary symptoms. Blood cultures should be obtained in any febrile and acutely ill-appearing patient [2].

Cross-sectional imaging is a key component in the evaluation of patients with a suspected intra-abdominal complication of CD [2]. Magnetic resonance enterography (MRE) is often considered the optimal imaging modality in pediatrics because it is radiation-sparing (Fig. 40.2). However, in the acutely ill child, standard computed tomography (CT) may be the most readily available option [5]. Cross-sectional imaging is able to demonstrate bowel wall thickening, bowel dilation, and mesenteric fat proliferation. Both CT and MR can detect presence of fistulae, particularly if utilizing oral contrast and performing full MRE or CT enterography (CTE) [2]. Bowel ultrasound (US), which is also radiation-sparing, can be useful in certain clinical scenarios as well, particularly serial monitoring for improvement or disease progression as well as detection of phlegmon or intra-abdominal abscess if performed and interpreted by an experienced team (Fig. 40.3) [5]. The administration of enteral contrast may improve the quality of bowel US [6]. US can be limited by bowel gas, which is not an issue with CT or MR [2]. Lastly, magnetic resonance imaging (MRI) of the pelvis is usually the modality of choice to evaluate complicated perianal disease [7]. One challenge is successfully being able to distinguish a phlegmon, which is an inflammatory mass, from a pus-filled abscess cavity, particularly in cases of extensive bowel inflammation. CT, MR, and ultrasound may allow for this differentiation using presence of gas, fluid, and/or color Doppler signals, though without these clear features, discerning abscess and phlegmon can be difficult in practice [8]. This can be a clinically critical delineation, as phlegmons cannot usually be drained, while drainage is a mainstay of abscess treatment, as described later in this chapter.

The role of endoscopy in the evaluation of intra-abdominal abscess has not been well defined in the literature. In general, endoscopy can be useful to better define overall disease activity and assess for infectious complications of disease or immunosuppression, such as cytomegalovirus, and may provide guidance for overall disease management, particularly when surgery is being considered [2]. However, there is concern regarding higher rate of complication of endoscopic assessment in the setting of an active abscess secondary to penetrating disease. Optimal timing of endoscopy following treatment of intra-abdominal abscess is also debated, with most sources citing a window of 4–6 weeks after therapy as the ideal interval [1].

Antimicrobial coverage is indicated in all cases of intra-abdominal and pelvic abscess and is aimed at enteric gram-negative aerobic and facultative bacilli, enteric gram-positive streptococci, and obligate anaerobic bacilli [1]. Coverage should also target nosocomial pathogens, as many patients with CD and abscess will have had multiple exposures to the healthcare system [2]. Initial broad-spectrum options include a carbapenem, a B-lactam/B-lactamase inhibitor combination, or an advanced-generation cephalosporin, plus metronidazole [2]. Narrowing of coverage may be possible if abscess material is obtained for culture and sensitivity. Consulting with an infectious disease specialist can provide additional guidance related to local resistance patterns and other special considerations such as recent antibiotic exposure [2].

Route of administration of antimicrobials has not been directly compared in the literature, but the decision regarding parenteral versus oral antibiotics is usually determined based on the clinical course and severity [1]. Duration of therapy depends primarily on the ability to successfully drain the collection. Antibiotics are usually continued for 3–7 days after successful drainage [9]. Longer courses are required if the abscess cannot be drained adequately [1].

Some adult studies have shown that antibiotics alone, without percutaneous or operative drainage, can be successful in the treatment of CD-related intra-abdominal abscesses. Cases that may be more likely to respond to medical management alone include abscesses of small size (<3 cm), absence of associated fistula(e), and patients who are immunomodulator-naïve [10–13]. Despite these described associations in several studies, there are not clear indications for which patients will respond to this approach [1]. The recurrence rate after medical treatment for intra-abdominal abscess in CD ranges from 37 to 50% [1].

Percutaneous abscess drainage is performed by positioning a catheter or drain into the abscess cavity guided by imaging techniques such as ultrasound or CT scan [10]. In the past, this technique was avoided because of the perceived risk of creating a post-drainage enterocutaneous fistula, but more recent studies have shown favorable results in certain clinical scenarios [2], particularly since the advent of biologic therapies to treat CD [1]. It is done in conjunction with antibiotics and can either serve as definitive therapy or as an intended bridge therapy prior to a surgical procedure [10]. There are also cases of failure of percutaneous drainage to fully treat the abscess where eventual surgery is required [10].

Factors related to success of percutaneous drainage have been described to include abscess size, number, etiology, location, presence of fistula, and proximity to vital structures (10), though studies have shown mixed results when analyzing these variables. In general, a unilocular, well-defined cavity, >2–3 centimeters in size, without direct contact with major vessels or organs, is most likely to be successfully drained [14]. The expectation is that clinical improvement should be seen within 3–5 days after drain placement, with decreasing volumes of drainage [10]. When drainage decreases to <10 mL/day (5 mL/day in neonates), and the patient is clinically improved, the drain can be removed [2, 15]. If clinical improvement is not seen, reimaging is indicated to reassess if abscess has been drained adequately. If it has not, repositioning of the drain or plan for surgical intervention usually follows [10].

Persistent drainage raises the concern for fistula formation, in which case an abscessogram can be performed using injected contrast [2]. Studies examining continued treatment with the percutaneous drain combined with medical therapy, bowel rest, and parenteral nutrition have reported varying success in addressing these fistulae [16–18].

Rypens and colleagues published a retrospective series of 14 pediatric patients with CD and intra-abdominal or pelvic abscess who underwent percutaneous abscess drainage as an initial intervention. All but two patients eventually had the affected bowel segment resected, though the authors indicated definitive surgical management was the preferred therapy at their institution; thus, percutaneous drainage had not been intended to be definitive therapy. They concluded that, following the percutaneous drainage, the patients had improved clinical status prior to surgery, which was thought to contribute to a less invasive and technically easier surgical procedure [19]. Other studies, which were not designed to examine this exact question, have shown reduced postoperative complications in patients who have percutaneous drainage preoperatively [20–22].

Percutaneous drainage is a relatively safe procedure [14]. Complications have been reported in approximately 5–11% of cases and include sepsis, small bowel fistulae, colon perforation, and death [14, 19]. Minor complications such as bacteremia or infection at the catheter site have been reported in about 3% of cases [14].

Traditionally, surgical drainage had been the primary treatment option for intra-abdominal abscesses in CD [10]. Surgical drainage of intra-abdominal or pelvic abscess involves exploration of the region, evacuation of all abscess contents, irrigation and debridement of the abscess cavity, and commonly resection of the affected bowel [1]. Importantly, surgical resection of diseased bowel is not considered curative in Crohn disease as postoperative recurrence of disease, particularly at the surgical anastomosis, is common. Surgical drainage can be associated with significant morbidity, particularly as it is performed in ill patients. Potential complications include wound infections, small bowel fistulae, and anastomotic leakage [10]. Often ostomy creation is indicated or cannot be avoided [10].

As will be discussed in more detail in the following section, surgical intervention may be necessary when medical and percutaneous drainage measures are unsuccessful in achieving abscess resolution and, in some cases, may be the primary intervention selected along with antimicrobial therapy and CD-specific treatment, based on a variety of factors [2]. General principles of surgical management include preservation of intestinal length and resection with macroscopically disease-free margins [2]. Laparoscopy has become the preferred approach over time due to the benefits of shorter postoperative recovery time, decreased wound-related complications, formation of fewer intra-abdominal adhesions, and better cosmesis when compared to an open approach [23]. Laparotomy, however, is still considered a safe and reasonable approach in patients who cannot tolerate or have too many adhesions from prior surgery to allow the insufflation of the abdomen with carbon dioxide needed for laparoscopy [2]. Diverting ileostomy or colostomy may be necessary when there is significant intra-abdominal soilage, inflammatory thickening of the intestinal wall, and intraoperative instability precluding safe additional operating time to construct an anastomosis [2]. Ostomy creation may be temporary.

Complication rates vary in the literature but have been reported to be as high as 25% [24] and may be influenced by several factors, including preoperative percutaneous drainage, discussed in more detail in the next section. Otherwise, weight loss, number of structures involved in the inflammatory mass, peritonitis and free air, smoking, and previous intestinal surgery have also been associated with postoperative complications [25]. Nutritional status and decreasing steroid dose may reduce surgical complication rates [2] and are discussed in more detail in later sections of this chapter.

Several studies have retrospectively analyzed outcomes of percutaneous drainage compared to surgical drainage of intra-abdominal abscesses in CD [10]. Consistent conclusions are difficult to draw, however, given the mostly retrospective nature, mixed results, and small sample sizes. The decision regarding initial intervention therefore continues to be a challenging one, and treatment strategy for each individual patient continues to be based on patient factors and experience and practice patterns of the treating physicians and institutions.

To address the question of efficacy, the most recent and comprehensive assessment of prior retrospective studies is a meta-analysis by He and colleagues published in 2015. The authors compared clinical outcomes between percutaneous drainage (with or without further elective surgery) and initial surgery in adult patients with CD-related intra-abdominal abscesses [26]. Nine studies involving a total of 513 patients were included. In five studies, percutaneous drainage was used as a definitive therapy and compared to initial surgical management; four of the studies compared surgical outcomes in those patients who first underwent preoperative percutaneous drainage and those who did not. When initial percutaneous drainage was compared to surgery, there were no significant differences between groups regarding patient sex, previous abdominal surgery, abscess location, single or multiple abscesses, abscess size, perioperative immunomodulator or steroid use, or length of follow-up period.

While several previous studies have indicated success with percutaneous drainage as definitive management of intra-abdominal abscesses [27–30], this larger meta-analysis found that over one third of patients treated by percutaneous drainage as the intended definitive therapy did ultimately require surgery [26]. Even when eventual surgery is needed, several studies suggest preoperative percutaneous drainage is beneficial, contributing to less surgical technical difficulty and decreased risk of ostomy creation [1, 19]. Given the multitude of factors contributing to success and risk in both options, there may still be a subset of less ill patients with intra-abdominal abscess who will do quite well with percutaneous drainage. In fact, there were 12 patients identified in one study who successfully underwent percutaneous drainage procedures on an outpatient basis and received oral antibiotics at home [31].

Regarding safety, several studies have reported increased complication rates in patients undergoing surgical drainage compared to percutaneous drainage, specifically longer lengths of stay in the hospital [31] and increased need for ostomy creation [26, 32]. Another study noted fewer postoperative complications in patients who first underwent percutaneous abscess drainage, including anastomotic leaks, postoperative abscess formation, intestinal fistula, leaks of intestinal stumps, and leaks of sutured secondary internal fistulae, though these trends (25% vs. 11% complication rates) did not reach statistical significance [25]. Again, there are potential biases in these analyses as more severe illness and disability may be present in the patients who were treated primarily surgically [31]. In the large recent meta-analysis by He and colleagues, initial surgery was associated with significantly higher overall complication rate compared to initial percutaneous drainage. However, there was no difference in rates of specific complications such as enterocutaneous fistula, wound infection, anastomotic leak, postoperative abscess, and recurrent abscess [26]. There may be some advantages to preoperative percutaneous drainage to decrease overall complications, but data regarding this question was mixed. Four studies showed a decrease in complications when percutaneous drainage was used prior to surgery but three showed comparable complication rates [26].

To date, randomized controlled trials comparing the two approaches are lacking [1, 10]. Several consensus guidelines including the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) [2] and the American College of Radiology [12, 13] have recommended percutaneous drainage as an initial step, provided it is technically feasible [10]. When abscesses are not amenable to percutaneous drainage because of size or location, or persist despite percutaneous drainage and antimicrobial therapy, surgical drainage is warranted [10].

A phlegmon is an ill-defined inflammatory mass that can form as a result of a sealed-off perforation. Phlegmons in CD typically involve the mesentery and adjacent loops of bowel. Though it is known that penetrating disease affects 40% of CD patients within the first 5 years of diagnosis, there are no specific data related to prevalence of phlegmons [33]. One review of about 350 adult patients with CD who had median duration of disease of about 10 years reported penetrating disease in 20% and phlegmon in 3.4% using CTE [34]. Treatment has traditionally included antibiotics, bowel rest, drainage of an associated abscess collection if present, and eventually surgical resection of the mass. CD-specific medications may also play an important therapeutic role as described in the next section [33]. In the future, radiologic terminology may be moving away from the term “phlegmon” to more illustrative descriptions of findings, such as “inflammatory mass with or without abscess.”