Keywords
anorectal malformations - ultrasound - diagnostics - reconstructive surgery
New Insights and the Importance for the Pediatric Surgeon
High-resolution transperineal ultrasound with 3D reconstruction seems to have the
potential to replace the augmented pressure distal colostogram in anorectal malformations
(ARM). This would allow a radiation-free assessment of the patients prior to the reconstructive
surgery, drastically changing the current diagnostic algorithms in ARM.
Introduction
Anorectal malformations (ARMs) consist of a wide spectrum of defects with an estimated
incidence of 1:5,000 live births.[1] Management relies on the correct identification of the rectum's location and its
relationships to the urinary tract and bony structures of the pelvis.[2] At present, the gold standard for diagnosis is the augmented-pressure distal colostogram
which exposes patients to significant radiation.
We present a new technology called 3D tomographic ultrasound (tUS), that can potentially
replace the distal colostogram without radiation exposure, which we tested on four
newborn males with imperforated anus and no visible fistula. The technology employed
(PIUR Imaging systems) connects a regular ultrasound transducer through digital video
output (ex. HDMI) with an applied independent clip-on sensor device. During the sonography
the two-dimensional images are transferred to the software (PIUR Infinity Workstation)
in real time. The 3D picture is generated with a semi-automated segmentation process
and can be visualized on any connected computer.
To our knowledge this is the first attempt to apply transperineal, high-resolution
ultrasound with additional 3D tomographic diagnostics to patients with ARM prior to
definitive corrective surgery.
Case Series Report
Four full-term male newborns with imperforated anus were referred to our center at
day 1 of life. As none presented signs of a perineal fistula, a diverting colostomy
was performed in the first 48 hours. The descendostomy was performed according to
standard with a separate mucous fistula to the distal colonic segment[3] and all patients underwent complete VACTERL screening. Complete clinical data of
the four patients is illustrated in [Table 1].
Table 1
Clinical data of the reported cases
|
Patient 1
|
Patient 2
|
Patient 3
|
Patient 4
|
|
Gestational age of birth (weeks)
|
366/7
|
382/7
|
390/7
|
385/7
|
|
Weight at birth
|
2910 g
|
3180 g
|
3240 g
|
2990 g
|
|
Visual appearance at birth
|
ARM with no visible fistula
|
ARM with no visible fistula
|
ARM with no visible fistula
|
ARM with no visible fistula
|
|
Meconium in the urine
|
No
|
No
|
Yes
|
Yes
|
|
Comorbidities
|
Hypospadia, hydronephrosis I right kidney with multiple dysplastic cysts, small VSD,
ASD II
|
Hydronephrosis I-II left kidney
|
Hydronephrosis I-II right kidney
|
None
|
|
Age at colostomy (days)
|
2
|
2
|
2
|
1
|
|
Age at colostogram date (days)
|
16
|
8
|
6
|
8
|
|
Age at perineal US (days)
|
16
|
8
|
6
|
8
|
|
Diagnosis according to colostogram and perineal US
|
ARM with recto-bulbar fistula
|
ARM with recto-prostatic fistula
|
ARM with recto-bulbar fistula
|
ARM with recto-prostatic fistula
|
|
Age at PSARP (days)
|
58
|
50
|
45
|
87
|
|
Follow-up (weeks postop)
|
55
|
55
|
25
|
10
|
Preoperative assessment was performed through augmented pressure distal colostogram
and high-resolution transperineal ultrasound with 3D tomographic reconstruction. The
same ground principles of the standard colostogram were applied to the sonographic
evaluation.[4] A Foley catheter was introduced in the mucous fistula and the injection of normal
saline solution (0.9% NaCl) assured the dynamic visualization of the recto-urethral
fistula. A high-resolution linear probe (14 Mhz transducer; Toshiba 14L5) with the
PIUR tUS Infinity system add-on (Piur Imaging GmbH Vienna, Austria) was positioned
on the perineum ([Fig. 1A]). After documentation of the anatomy in B-mode (including video loops), the add-on
scan was performed by parallel probe sliding from left-to-right in a single acquisition
(with video documentation). The distinction between recto-bulbar (two cases) and recto-prostatic
fistulas (two cases) was possible by direct identification of the fistula relative
to the rectum and the urethra, as well as indirect visualization of the prostate ([Fig. 1B], [C]).
Fig. 1 High resolution perineal ultrasound images: position of the linear transducer with
PIUR tUS Infinity System add on mediansagittal at the center of the perineal body,
patient supine held in lithotomy position, foley cathter in the mucous fistula. (A); recto-bulbar fistula (B); recto-prostatic fistula (C).
The 3D tomographic reconstruction was then automatically generated by the PIUR tUS
Infinity system through threshold-based automatic segmentation of the images ([Fig. 2]). Although the diagnosis was already apparent by high-resolution transperineal ultrasound
in B-mode, the 3D reconstruction was found valuable for the planning of surgery, as
well as for the illustration of the ARM to the parents. The images offered a better
spatial visualization of the anatomy.
Fig. 2 3D reconstruction process: on the left side respectively two coronal (A, B) and two sagittal cuts (C, D) created from the ultrasound acquisition, which are used to automatically reconstruct
the structure, shown on the right side (E).
In all cases the results of the distal colostogram nicely correlated with the high-resolution
transperineal US by B-mode and tUS ([Fig. 3A]–[D]). It is to be noted that the observers were not blinded to the results of the two
investigations, but the diagnoses resulted concordant regardless of the order in which
the two were performed. Indeed, the type of malformation identified was consistent
both when the perineal tUS followed the distal colostogram and in the cases where
it preceded it.
Fig. 3 Comparison between distal colostogram (A, C) and the automatically 3D reconstructed structures, including bladder, urethra, and
recto-urethral fistula, acquired from the linear ultrasound imaging (B, D) from the same patient. A and B show a recto-bulbar fistula, C and D a recto-prostatic fistula. The star indicates the rectum, the diamond shape of the
bladder, and the arrow points to the recto-urethral fistula.
All the investigations were performed in the presence of the parents, to ease the
distress of the patients. Our impression was that the absence of the lead gown during
the ultrasound, as well as the setting itself of the dark sonography room, concurred
in reducing the discomfort of the babies during the examination.
Posterior sagittal anorectoplasty (PSARP) was performed in all cases with no complications
and intraoperative findings were equally concordant with the imaging studies. Postoperative
course was uneventful in all cases.
Discussion
At present the augmented-pressure distal colostogram is the gold standard for the
preoperative assessment of ARMs without a visible fistula.[5] This examination, if adequately performed, allows the correct identification of
the type of malformation, the location of the rectum, and presence of a recto-urinary
fistula.[2] Errors in performing the preoperative imaging occur mostly due to inadequate application
of pressure to the distal colostomy to overcome the muscle tone of the funnel-like
striated muscle, which may induce to misinterpret the malformation as high and without
fistula. In such cases, the risk of damaging adjacent structures such as the urethra,
vas deferens, and seminal vesicles increases significantly.[6] Therefore, an attempt to reduce exposure to radiation, which is a known drawback
of the distal colostogram, cannot be perpetuated at the cost of sacrificing the ground
principles of this investigation. For this reason, MRI-fistulograms,[7] although potentially useful in combining the evaluation of the anatomy of the ARMs
and the screening of associated malformations such as presacral masses and sacral
ratio,[8] are not sufficiently reliable and have not gained space in the preoperative assessment
of the ARMs.
Transperineal high-resolution ultrasound with 3D tomographic reconstruction can on
the other hand be performed dynamically, keeping the same fundamental principles of
the distal colostogram and assuring the application of adequate pressure to visualize
the fistula. It also offers the advantage of a quick bedside testing method. Based
on this premise, replacing the fluoroscopic examination with a sonography seems possible
with sufficient experience, most likely after a supervised run-in phase with both
methods performed and re-evaluated systematically. Other than the absence of radiation
exposure, ultrasound offers a more comfortable setting both for the babies and for
their families. Furthermore, high resolution transperineal ultrasound can detect presacral
masses, thus further allowing the screening for Currarino syndrome, possibly replacing
MRI in this context in newborns.[9]
As for the evaluation of the relationship between the rectum and the bony structures
of the pelvis, which is crucial for the choice of surgical approach, this appears
possible in the sonographic evaluation since both the sacrum and the pubic symphysis
are clearly visible in the images ([Fig. 1B, C]). Although promising, reliability needs to be assessed through a prospective trial
before conclusions can be drawn in this regard.
Further studies with a higher number of patients, broader spectrum of disease (ARM
with no fistula or with bladder-neck fistulas), and different age groups as well as
blinded investigators are necessary to evaluate the reliability of high-resolution
transperineal ultrasound with 3D tomographic reconstruction in the diagnosis of ARM.
Still this new technology merits attention and has the potential to drastically change
diagnostic algorithms in ARMs.
Conclusion
Based on our promising results, we envision high resolution transperineal ultrasound
with 3D tomographic reconstruction to hold the potential to replace the distal colostogram
at tertiary referral centers.
