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Thứ Sáu, 26 tháng 4, 2013

Enterovesical Fistula: Sonographic Diagnosis

A 73-year-old man presented to the emergency department after noting dysuria and fecal matter in his urine for 1 day. The patient had a medical history consisting of prostate cancer treated with brachytherapy, Crohn disease, colonic stricture, diabetes, and no prior surgeries. Other than episodic lower abdominal pain that had been occurring for months, the patient did not have any additional symptoms, denying any fever, chills, vomiting, diarrhea, constipation, rectal pain, chest pain, or dyspnea.
On initial examination, the patient was in no acute distress, afebrile, and hemodynamically stable. His abdomen was soft with mild tenderness of the lower abdomen without palpable masses, guarding, rigidity, or rebound. There was no scrotal or inguinal swelling or tenderness. Initial laboratory results were notable only for a white blood cell count of 14,100 cells/μL with 88% neutrophils and a venous lactate level of 0.83 mmol/L. Fecal matter was noted on gross examination of the urine, and urinalysis results were negative for nitrite, positive for leukocyte esterase, and showed more than 182 white blood cells per high-power field and many bacteria.
Point-of-care sonography was performed by the emergency physician using a curvilinear transducer (Figure 1, A and B, and Video 1) and revealed a collection of mixed echogenicity throughout the bladder, representing stool, along with multiple hyperechoic foci with a reverberation artifact and shadowing, consistent with pneumaturia. A hyperechoic band leading from the bowel into the bladder was noted, consistent with a fistula. A computed tomographic (CT) scan of the abdomen and pelvis (Figure 1C) was obtained to assess for associated intra-abdominal disease and to provide further anatomic detail given the patient’s complicated history. Computed tomography revealed a heterogeneous collection of soft tissue and fecal matter within the pelvis bordering the posterosuperior wall of the bladder and air within the bladder, supporting the diagnosis of an enterovesical fistula. Subsequent surgical exploration and cystoscopy confirmed a colovesical fistula from the distal sigmoid to the left bladder near the left ureteral orifice and copious stool within the bladder.
Enterovesical fistulas are classified as colovesical, which is the most common form, rectovesical, ileovesical, and appendicovesical. Most commonly a complication of diverticulitis, malignancy, or Crohn disease,1 fistulas may also occur after trauma, pelvic surgery, or pelvic radiation therapy, including brachytherapy.2 The fistula is often difficult to identify on imaging studies; hence the lack of a reference standard imaging modality.3 The most sensitive and commonly recommended initial study is CT,1,3 although the fistula itself is not consistently identified.37 Findings used to confirm the presence of a fistula include gas in the bladder in patients without recent urinary instrumentation, local colonic thickening immediately adjacent to an area of locally thickened bladder, and oral contrast medium in the bladder on nonintravenous contrast-enhanced CT.1,4,8 Alternatively, intravenous contrast medium noted within the bowel when an oral contrast medium is not used also implies the presence of a fistula.6
Like CT, sonography can visualize soft tissue in multiple planes and has been used in the diagnosis of colovesical fistulas.911 Suggestive findings include pneumaturia, which is represented by multiple reverberation artifacts within the bladder, and stool within the bladder, which is hyperechoic.9,10 The fistula itself appears hypoechoic,12 but if gas is present in the tract, the fistula may instead be visualized as a hyperechoic “beak” connecting the peristaltic bowel lumen and the bladder. Air bubbles or hyperechoic material may be noted flowing from the beak into the bladder with direct compression either manually or using the ultrasound transducer.9,11 This finding must be distinguished from ureteral jets emanating from the ureterovesical junction due to normal peristalsis of the ureter.9,11

Figure 1.
Enterovesical fistula in a 73-year-old man. A and B, Longitudinal (A) and transverse (B) views of the suprapubic window illustrating the bladder (B) with a hyperechoic artifact consistent with air (A) and heterogeneous material consistent with stool (S). There is a hyperechoic band connecting the bowel to the inside of the bladder, consistent with a fistula (F). C, Transverse CT scan of the pelvis illustrating air within the bladder.
In contrast to CT, sonography is used infrequently in the initial evaluation of suspected enterovesical fistulas. In addition to identifying the presence of a fistula, CT may reveal associated intra-abdominal processes and provides anatomic details for any surgical planning. There are also limited data regarding the sensitivity of sonography for diagnosing these fistulas. Sonography did not identify any fistulas in 27 patients from 3 retrospective studies with confirmed enterovesical fistulas.3,4,13 In another retrospective study of patients with colovesical fistulas secondary to diverticulitis, sonography identified a fistula in 1 of 23 patients.14 None of these studies, though, describe the experience of the sonographers or specific imaging protocols. In a prospective study by Maconi et al,15 sonography enabled the diagnosis of all 4 enterovesical fistulas in patients with Crohn disease who underwent surgical intervention.
The diagnosis of an enterovesical fistula is strongly suggested by the presence of fecaluria, pneumaturia, or recurrent urinary tract infections, but it may present more subtly. Fewer than half of affected patients have fecaluria, and although pneumaturia is found in approximately 60% of patients, other causes such as recent bladder instrumentation and emphysematous cystitis must be considered.1 Although this patient presented with classic signs of an enterovesical fistula, this case shows that point-of-care sonography can be used to make the diagnosis. As it is performed at the bedside, it may be used early in the course of evaluation, especially when the patient’s presentation is less clear and CT not immediately indicated. Findings suggestive of a fistula, including air or stool in the bladder, or visualization of the fistula itself, can lead to timely diagnosis of this disease process. Furthermore, especially if pain, fever, and unstable vital signs are present, point-of-care sonography allows for concomitant evaluation for other possible causes of these symptoms and guiding of further interventions.

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