Sonographic rectal enema (“hydrocolon”) for diagnosing large bowel pathologies in infancy – pictorial review to demonstrate feasibility and value

Pathologies of the large bowel in infancy include several different entities with commonly overlapping clinical presentations. The diagnostic algorithms are mostly based on an institutional consensus, and the evidence is limited⁽¹⁾. The role of sonography as the first-line modality is unquestionable. However, if baseline sonography does not deliver satisfying results, a complimentary ultrasound (US) enema (also referred to as “hydrocolon”) may be conducted⁽²⁾.

For the “hydrocolon” procedure, pre-warmed saline is applied via a small rectal non-balloon-tip tube by low-pressure drip infusion or manually by a syringe. The filling volume is variable, depending on age and the degree to which the colon needs to be distended. During the enema, the progress of colonic filling and distension is monitored continuously. For therapeutic enemas, slightly higher filling pressures may result in backwash through the ileocecal valve into the terminal ileum. For diagnostic purposes, no anal occlusion is needed. This prevents overpressure, and thus, the risk of perforation is negligible. With isotonic saline, no significant fluid shifts occur.

The fluid-filled state (Fig. 1) of the bowel enables a detailed examination of wall stratification, thickness, distensibility, and peristalsis. Moreover, any potential pathological content such as a polyp or meconium plug can be depicted. In conditions like intussusception or meconium plug syndrome, US enema serves as a therapeutic option as well.

Fig. 1

High-frequency linear or micro-curved abdominal transducers are applied for US enema, with typical settings for bowel imaging. Some experience of the investigator is advisable; in case of bowel perforation, US enema is contraindicated.

The purpose of this overview is to present common and less common bowel pathologies in neonates and infants, where performing US enema may prove useful.

This retrospective study was approved by the institutional review board (EK 31-506 ex 18/19); no written informed consent was required from the parents/guardians of study participants. The authors declare no conflicts of interest.

Failure to pass meconium in the first 24 hours of life raises the suspicion of intestinal obstruction. Retained meconium might be associated with diverse pathologies, such as meconium obstruction syndrome, atresia, or Hirschsprung’s disease. In meconium ileus, sticky meconium accumulates in the distended (terminal) ileum. In contrast to this, a collapsed terminal ileum and disproportionately dilatated proximal small bowel loops can be found in ileal atresia. Both latter disease entities may be associated with microcolon. In meconium plug syndrome, meconium balls may occur in both small and large intestine, which is associated with small left colon and normal-sized rectum. In both conditions, a repeated “hydrocolon” can be utilized to mobilize meconium balls, as shown in Fig. 2. A diluted isotonic radiopaque contrast agent may be added to saline enema ‒ not only to improve the therapeutic result but also for additional radiographic assessment. A transition zone to the microcolon or small left colon may also be delineated⁽³⁾.

Fig. 2

In intussusception, a proximal bowel loop slips into the distal one. A cut-off diameter of 2 cm is commonly suggested to differentiate between ileoileal and -colic intussusception. The diagnosis is mostly straightforward, based on typical “pseudokidney” and “doughnut” signs (Fig. 3). However, sometimes, especially in recurrent intussusception, the US appearance can be confusing, and a “hydrocolon” procedure may be helpful for differentiation. Furthermore, high-pressure “hydrocolon” (hydrostatic US reduction) is a well-established method for the reduction of intussusception without radiation exposure⁽⁴⁾.

Fig. 3

The spectrum of abdominal masses comprises several entities. By clarifying the relationship between the mass and bowel, US enema may help to reduce the number of possible differential diagnoses. Bowel polyps (Fig. 4) are rare findings in infants and have variable morphology and localization. They can appear sporadically or as part of a syndrome (e.g., juvenile polyposis). With the application of “hydrocolon”, the intraluminal localization as well as the diagnosis can be clearly confirmed (Fig. 4).

Fig. 4

Infantile (<2 years) and very early onset (<6 years) IBD are rare conditions. Most commonly, these patients suffer under colonic mucosal and perianal disease. Complications such as mesenteric abscesses and higher fistulae are uncommon. Therefore, small-bowel imaging might be restricted to detecting inflammation⁽⁵⁾, which is reliably performed by US without anesthesia. US enema may increase the overall sensitivity of the imaging technique even in the distal colon and the rectum, where US is usually challenging to perform (Fig. 5).

Fig. 5

In (early) childhood, colonic stenosis is mostly a late complication of bowel inflammation (e.g., necrotizing enterocolitis); the congenital origin is rare. Fluoroscopy is widely used for assessing these conditions. The advantage of US over fluoroscopy is the possibility to analyze the bowel wall and the surrounding structures; thus, a potential external compression can be assessed as well. Dynamic analysis during saline enema helps differentiating between colonic stenosis and transient localized spasm or collapse, as well as estimating the extension of the affected bowel segment (Fig. 6).

Fig. 6

Although US “hydrocolon” is not a new player in the diagnostic arsenal for bowel pathologies, there are just a few reports in the literature addressing this modality. In this review, the authors provide examples of bowel pathologies, where the use of US enema is is diagnostically useful. This easy-to-access method may shorten the diagnostic work-up and spare radiation exposure as well as the use of contrast agents. However, the diagnostic performance highly depends on the experience of the performing radiologists.