Keywords
anorectal malformations - H/N type rectourethral fistula - transperineal ultrasound
Introduction
Anorectal malformations (ARMs) encompass a complex spectrum of congenital anomalies
involving the distal rectum and anus as well as urinary and or genital systems.[1] H/N type anorectal malformations are extremely rare, usually seen in females. In
boys, they are associated with increased rates of major congenital anomalies.[2]
[3] In the presence of colostomy, an augmented pressure colostogram with or without
retrograde or micturating cystourethrogram is the investigation of choice.[2]
In children, transperineal ultrasound (TPUS) has been used in the evaluation of anorectal
malformations, Müllerian anomalies, and disorders of sex differentiation (DSDs).[1]
While augmented pressure colostogram is the gold standard for characterization of
ARM and MRI is ideal for pelvic floor muscle assessment, TPUS offers a good combination
of both these utilities.[4]
[5] Here we describe the role of transperineal ultrasound as an adjunctive modality
in the diagnosis of one such complex anomaly.
A 2-year-old male child patient complained of passage of urine from the anal canal,
and occasional passage of a few drops of urine from the external urethral meatus.
He had no incontinence or fecaluria. Local examination showed a narrow external urethral
meatus, not admitting a 5 Fr infant feeding tube. Anal opening was seen at normal
site. Abdominal ultrasound was normal.
Retrograde urethrogram (RGU), performed using a 20 gauge cannula, showed opacification
of both the bladder and rectum. The anterior urethra was severely attenuated in caliber,
with acute angulation at the bulbo-membranous junction ([Fig. 1]). However, an obvious fistulous tract was not demonstrated. TPUS performed with
high-resolution linear transducer (7–10 MHz) showed a hypoechoic tract between the
urethra and anterior wall of the rectum, indicating a fistula ([Fig. 2]). Micturating cystourethrogram was performed on a separate occasion after retrograde
bladder filling through the distal urethral cannulation. It showed a H/N type rectourethral
fistula between the prostatic urethra and anorectum ([Fig. 3]).
Fig. 1 RGU image showing irregular attenuated urethra and an angulation at posterior urethra.
Radio-opaque external marker is placed at anal canal.
Fig. 2(A-D). Transperineal US with the child in supine lithotomy position and the probe placed
in mid sagittal and slight parasagittal plane (A - original, B- annotated). The fistula tract originates from the posterior urethra after a short
distance from UB neck, and ends in the anterior wall of anal canal. Inverted image
(C- original, D- annotated) for comparison with urethrogram shows the course of urethra (orange),
fistula (torquiose), and anal canal anterior wall (yellow).
Fig. 3 (A, B). MCU image shows the microurethra ending in orthotopic meatus, and fistula tract
opening in the anal canal. Annotated image (B) showing the ‘H’ shape of the urogenital tract anatomy, similar to that seen in TPUS
([Fig 2]).
Discussion
H-type configuration is an extremely rare variant in the spectrum of anorectal malformations
described under the recent Krickenbeck classification.[3] It differs from other ARMs in the fact that usually the anal opening is in normal
location[3]
[4]. Majority of these patients have relatively continent sphincters, and abnormal passage
of urine through the anal canal is often the only clinical clue. Therefore, imaging
plays an important role in the diagnosis, and exact delineation of anatomy.[5] Cologram offers an objective demonstration of the anomaly; however, with proper
technique and expertise, TPUS can replicate the same critical anatomical detail.[5]
[6] Moreover, the orthotopic urethra is often narrow, thereby making MCU difficult and
posing imaging challenges in a child who has not undergone colostomy.[5] This was the situation in our patient, where TPUS added significant imaging input
and guided further intervention. By demonstrating a sound fistulous tract anatomy,
TPUS offers a potential role in differentiating low or intermediate/high variety of
anorectal malformation. Simultaneous evaluation of internal pelvic anatomy and dynamic
evaluation of pelvic floor muscles were additional benefits.[4]
[6] The study was performed without sedation, which also is a great advantage.
The main challenge in TPUS lies in its operator dependence, and long learning curve.[5] Nevertheless, its increased use as adjunct technique can improve diagnostic confidence
in difficult cases.
