DOI:10.2214/AJR.07.3759
AJR 2008; 191:1250-1254
© American Roentgen Ray Society
Role of Endoluminal Sonography in Evaluation of Obstruction of the Ureteropelvic Junction
Ling Lin1,
Demetrius H. Bagley2 and
Ji-Bin Liu3
1 Department of Ultrasound, Huaxi Hospital of Sichuan University, Sichuan,
China.
2 Department of Urology, Thomas Jefferson University Hospital, Philadelphia,
PA.
3 Department of Radiology, Thomas Jefferson University Hospital, 7th Fl. Main
Bldg., 132 S. 10th St., Philadelphia, PA 19107.
Received February 1, 2008;
accepted after revision April 10, 2008.
Address correspondence to J. B. Liu
(ji-bin.liu{at}jefferson.edu).
Abstract
OBJECTIVE. The objective of this study was to evaluate the clinical
feasibility of the use of 2D and 3D endoluminal sonography during endourologic
procedures on patients with an obstructed ureteropelvic junction (UPJ).
SUBJECTS AND METHODS. In 45 patients with an obstructed UPJ
undergoing endoscopic procedures, a 6.2-French catheter-based ultrasound probe
(12.5 or 20 MHz) was inserted under endoscopic guidance into the upper urinary
tract for acquisition of 2D images for evaluation of UPJ structures and
construction of 3D volume images with a computer workstation. The role of 3D
in addition to 2D imaging for identification of abnormalities at the UPJ was
evaluated.
RESULTS. Both 2D and 3D images depicted crossing vessels at the UPJ
in 24 of 43 patients (55.8%) and a ureteral septum in 14 of 43 patients
(32.6%), and endoscopic incisions were successfully made with sonographic
guidance. The anatomic structures of the UPJ associated with abnormalities
(e.g., crossing vessels, septum, calculi, tumors, and strictures) were
appreciated and evaluated more fully on 3D than on 2D images. The endoluminal
sonographic findings helped rule out or modify the interventional procedure
(endopyelotomy or balloon ureteroplasty) in the cases of eight of 43 patients
(18.6%).
CONCLUSION. Three-dimensional endoluminal sonography clearly
displays diagnostic information that complements 2D imaging findings and
enhances the assessment of normal and abnormal structures at the UPJ for
endourologic surgery.
Keywords: 3D • endoluminal sonography • endourology • imaging guided • ureteropelvic junction
Introduction
Catheter-based endoluminal sonography has been used for the evaluation of a
wide range of genitourinary abnormalities during en do urologic procedures
[1]. Although endoluminal
endoscopy enables direct inspection of the urinary lumen and luminal surface,
visual examination yields little information about the walls of the
genitourinary tract and adjacent structures. As a sectional imaging technique,
endoluminal sonography has high resolution for imaging below the surface of a
lumen and adds a third dimension (depth) to endoscopic examinations. Thus, it
can be a unique intraoperative imaging tool for endourologic procedures.
Conventional 2D endoluminal sonography of the upper genitourinary tract is
useful in several clinical scenarios. Two-dimensional images can depict
embedded submucosal calculi
[2], ureteral strictures, and
tumors [3]. One of the most
useful applications of 2D imaging during endourologic procedures is evaluation
of an obstructed ureteropelvic junction (UPJ) for detection of crossing
vessels and high insertion of the ureter
[4]. A limitation of
conventional 2D endoluminal sonography, however, is that images in the
longitudinal axis or parallel to the ureter cannot be obtained with current
transducer designs owing to the nature of the transluminal scanning
approach.
Three-dimensional digital tomographic techniques, such as CT and MRI, have
developed rapidly and have been gradually integrated into routine clinical
practice. Endoluminal sonography also lends itself to 3D image reconstruction.
To date, most attempts at 3D imaging with catheter-based probes have been in
intravascular sonography [5,
6]. The 3D imaging technique
allows more comprehensive evaluation of vascular morphologic features and
pathologic changes, which may be not appreciated on 2D images. This advantage
may apply to nonvascular endoluminal sonography, such as that of the
genitourinary tract. The objective of this study was to evaluate the clinical
feasibility of use of 2D and 3D endoluminal sonography during endoscopic
procedures on patients with obstruction of the UPJ.
Subjects and Methods
Patients
Forty-five consecutively registered patients with obstructed UPJ were
included in this study. The 21 women and 24 men had a mean age of 48 years
(range, 21–82 years). The upper urinary tract obstruction was confirmed
clinically and radiologically before surgery. Only patients who had undergone
an interventional endoscopic procedure, such as retrograde ureteropyelog
raphy, ureteroscopy, or planned percutaneous endopyelotomy, were included
because endo luminal placement of the catheter-based sonographic transducer
requires an endourologic procedure. All patients were fully informed of the
procedure, including the techniques and any potential benefits or risks, and
signed a consent form approved by the institutional review board. The study
was conducted in compliance with HIPAA regulations.
Instruments and Techniques
Endoluminal cross-sectional 2D images of the upper urinary tract were
acquired with a catheter-based sonographic probe. The probe consisted of a
6.2-French flexible catheter containing a single-element transducer with a
frequency of either 12.5 or 20 MHz (Sonicath, Boston Scientific). The image
obtained was a 360° cross section with a field of view that had a radius
of approximately 1–1.5 cm from the center of the probe. With the patient
under general anesthesia and in the supine position, retrograde pyelography
was performed at the beginning of the endourologic procedure to delineate the
anatomic features of the upper urinary tract. The catheter-based probe was
then inserted under endoscopic and fluoroscopic guidance into the upper
urinary tract for acqui sition of 2D cross-sectional images for evaluation of
the ureter and periureteral structures.
For 3D data acquisition, the catheter transducer was first positioned in
the renal pelvis or close to the segment of interest. A stepping motor (CIVS,
Boston Scientific) was used to smoothly withdraw the sonographic catheter
during the acquisition while images were continuously updated. In all cases,
the constant speed of 1.5 mm/s and a length up to 6 cm were used for pulling
the catheter to produce measurable data sets. The video output from the
sonographic system was connected to a dedicated 3D workstation (LIS 6000A,
Life Imaging Systems) for imaging acquisition, storage, reconstruction, and
postprocessing.
Three-dimensional reconstruction was achieved by stacking the 2D slices on
the basis of tomographic interfaces and pseudosurfaces through a process of
computed projections. To maximize acquired image quality, the internal frame
grabber on the 3D system was matched to the sonographic video output. This
frame optimization allowed collection of each image at full resolution, which
yielded slice-to-slice separation of 0.1 mm at a pullback rate of 1.5 mm/s.
Immediately after acquisition, the data were reviewed in multiplanar 3D format
and then stored in the 3D workstation. The volume images could then be
manipulated and presented in any plane (transverse, longitudinal, coronal, and
oblique views) for online or offline analysis
(Fig. 1). Reconstructed 3D
images of the obstructed UPJ were used to evaluate the normal and abnormal
structures and to compare with con ventional 2D images case by case. The
sonographic findings were used as a reference for surgical planning and
guidance of the endourologic procedures. The role of 3D in addition to 2D
imaging for identification of abnormalities at the UPJ was evaluated.
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Fig. 1 —45-year-old woman with simple ureteropelvic junction
obstruction. Endoluminal 3D image shows cross-sectional (CS), longitudinal
(L), and coronal (C) views of ureteropelvic junction with no evidence of
abnormality. RP = renal pelvis, UT = ureter, P = probe.
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Results
Endoluminal sonography was successfully performed on 43 of 45 patients with
UPJ obstruction undergoing endoscopic procedures. In two of the 45 cases,
access to the ureter could not be obtained. On the basis of both 2D and 3D
sonographic findings, eight patients were not considered candidates for
endopyelotomy because of the presence of crossing vessels without incision
windows in three cases, septum with an intervening vessel in two cases, long
(3.5 cm) narrow segment in one case, multiple cysts around the UPJ causing
obstruction in one case, and ureteral tumor invading into the UPJ in one case.
Thus intraoperative findings on endoluminal sonography alone ruled out or
modified the interventional procedure (endopyelotomy) in eight of 43 cases
(18.6%). These patients were later treated with laparoscopic or open
pyelotomy, cystic drainage, or balloon or stent placement. Among the eight
patients, four patients (three with crossing vessels and one with a septum and
crossing vessels) underwent laparoscopic or open surgery for the management of
UPJ obstruction. The intraoperative findings showed crossing vessels at the
UPJ and high insertion of the ureter, confirming the 2D and 3D sonographic
interpretations.
Both 2D and 3D endoluminal sonography depicted crossing vessels at the UPJ
in 24 of 43 patients (55.8%) and septum denoting high insertion of the ureter
in 14 of 43 patients (32.6%) (Fig.
2, Table 1). Other
abnormal findings included five cases of ureteral stricture
(Fig. 3), three cases of
calculus (Fig. 4A,
4B), one case of bifid renal
pelvis (Fig. 5), one case of
multiple cysts, two cases of adjacent small bowel (Fig.
6A,
6B), and one case of ureteral
tumor (Fig. 7A,
7B). For the 35 patients who
were candidates for endopyelotomy, sonographic localization was used to guide
the site of incision because it defined the anatomic features and the presence
and location of any crossing vessels or septa. Although both 2D and 3D imaging
findings were useful for guiding incision of the ureter (endopyelotomy) or
modifying the procedure, 3D imaging clearly showed the septum and crossing
vessels in the longitudinal and coronal orientations and was helpful for
intraoperative monitoring of the procedure to ensure the septum was removed
completely (Fig. 8A,
8B). No complications were
related to the sonographic procedures.
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Fig. 2 —48-year-old man with ureteropelvic junction obstruction with
crossing vessels and septum. Longitudinal and coronal 3D image shows ureteral
septum (S) and crossing vessels (V) in ureteropelvic junction. Spatial
relations of structures were easily and fully appreciated. P = probe, RP =
renal pelvis.
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Fig. 3 —59-year-old man with ureteropelvic junction obstruction with
narrow ureteral segment. Longitudinal 3D image of proximal ureter shows
evidence of narrow ureteral segment with echogenic area (arrows)
representing fibroconnective tissue. U = ureter.
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Fig. 4A —59-year-old man with obstructing proximal
ureteral–ureteropelvic junction calculi. Reconstructed multiplanar image
shows submucosal calculi (arrows) and vessels (V) at ureteropelvic
junction. P = probe.
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Fig. 4B —59-year-old man with obstructing proximal
ureteral–ureteropelvic junction calculi. Three-dimensional longitudinal
image shows multiple small fragments (F) of calculi. P = probe, RP = renal
pelvis.
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Fig. 5 —44-year-old woman with bifid renal pelvis (RP).
Three-dimensional image shows septum (arrows) dividing pelvis into
two portions. Length and thickness of septum are evident. Sonographic finding
is consistent with diagnosis of bifid pelvis.
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Fig. 6A —37-year-old man with ureteropelvic junction obstruction with
crossing vessel and adjacent small bowel. Two-dimensional image of proximal
ureter shows small bowel (SB) anterior to ureter and crossing vessel (not
shown).
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Fig. 6B —37-year-old man with ureteropelvic junction obstruction with
crossing vessel and adjacent small bowel. Reconstructed longitudinal view of
ureteropelvic junction clearly shows crossing vessel (V) and small bowel (SB)
and their relations to each other. RP = renal pelvis.
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Fig. 7A —58-year-old man with obstructing neoplasm at ureteropelvic
junction. Two-dimensional cross-sectional image shows hypoechoic tumor (T) at
region of ureteropelvic junction. P = probe, RP = renal pelvis.
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Fig. 7B —58-year-old man with obstructing neoplasm at ureteropelvic
junction. Three-dimensional reconstruction shows overall size and extent of
tumor. Distribution of tumor (T) and its relation to ureteropelvic junction
can be depicted only on 3D rendering. P = probe, RP = renal pelvis.
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Fig. 8A —65-year-old woman with ureteropelvic junction obstruction
with crossing vessels and septum. Three-dimensional image obtained before
endopyelotomy of obstructed ureteropelvic junction shows septum
(arrows) within renal pelvis and two crossing vessels (V) in anterior
aspect of longitudinal view.
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Fig. 8B —65-year-old woman with ureteropelvic junction obstruction
with crossing vessels and septum. Three-dimensional image shows septum was
successfully removed with endopyelotomy. This information was useful for
precise removal of septum to avoid damage to adjacent vessels (V).
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Discussion
The initial application of 3D sonography, evaluation of orbital lesions,
was reported as early as 1961 by Baum and Greenwood
[7]. Advances in technology,
particularly high-speed computing and storage hardware, have facilitated
application of 3D sonography to the evaluation of many parts of the human
anatomy. Over the years, great efforts have been made to develop
computer-based workstations and integrated 3D sonographic systems for
cardiovascular, obstetric and gynecologic, and abdominal imaging
[8].
Although 2D sonographic findings contribute to clinical management, it
sometimes is difficult to acquire a 3D impression of normal and abnormal
structures. The typical method of overcoming this problem is to scan
repeatedly through the region of interest to clarify the exact spatial
relations. This process can be tedious and time-consuming. In complicated
cases, it often is difficult for even specialists to understand
cross-sectional 2D images because abnormalities may not be present in all
sectional views.
We used a dedicated computer-based workstation to perform 3D reconstruction
of endoluminal sonographic images of the region of the UPJ. With the use of 3D
sonographic images, both radiologist and urologist can easily view the
reconstructed sectional images in any plane (transverse, longitudinal,
coronal, or oblique) during a procedure or afterward with offline evaluation.
Compared with 2D imaging, the perspectives available with this technique can
provide valuable information regarding anatomic and pathologic conditions. For
patients who are not candidates for endopyelotomy, 3D imaging findings are
useful for selection of alternative procedures (e.g., laparoscopic vs open
surgery).
Cross-sectional sonographic images of the upper genitourinary tract
reconstructed into a 3D display can be viewed from any image plane at any
selected site. In general, there is less definition of the ureteral layers
constituting the mucosa, muscularis, and adventitia, and these findings are
often very subtle on 2D cross-sectional images. The continuity of the mucosa
and muscularis from the ureter into the pelvis and the position of the
intramural ureter are better visualized on 3D images
(Fig. 1). Variations in the
diameter of the lumen along the long axial course are displayed on 3D
reconstructions of ureteral strictures. The length of the stricture and the
disruption of the normal architecture are readily apparent, thus ureteral
strictures causing UPJ obstruction are presented more precisely in 3D format
than on individual 2D images alone (Fig.
3). The region of the obstructed UPJ can be appreciated more fully
in 3D presentation.
Although the association between the UPJ and crossing vessels can be seen
on either 2D or 3D images, in our study the simultaneous association of
multiple vessels with variable courses was appreciated only with 3D rendering
(Fig. 2). The anatomic
structures of the UPJ associated with a variety of abnormalities also were
appreciated more easily in 3D representation (Figs.
4A,
4B,
5,
6A,
6B). A neoplasm adjacent to the
UPJ, which appeared as a hypoechoic mass, was clearly visualized and more
fully evaluated with 3D rendering than with 2D imaging (Fig.
7A,
7B). Although both 2D and 3D
findings provided useful information for guiding incision of the ureter
(endopyelotomy), 3D imaging more clearly showed normal and abnormal structures
in multiplanar views, adding valuable information for monitoring endourologic
procedures (Fig. 8A,
8B).
Although high-frequency 2D imaging yields high-resolution cross-sectional
views of the UPJ, reconstructed 3D imaging displays spatial morphologic
information, facilitating full appreciation of the anatomic and pathologic
features of the UPJ. For example, in the patient with a tumor at the UPJ (Fig.
7A,
7B), 3D imaging clearly showed
the size, location, and extent of the tumor and, more important, its relation
to the renal pelvis. The 3D findings helped obviate transureteral endoscopic
management of the tumor.
Conventional imaging of the upper urinary tract, such as CT and radiography
with intraluminal contrast enhancement, has been used but does not provide the
information acquired only with endoluminal sonography. Helical CT angiography
has been used to depict crossing vessels at the UPJ. In the controlled series
available
[9–11],
the vessels were less frequently visualized, and fewer vessels were detected
with CT angiography than with endoluminal sonography. In addition, CT
urography lacks the resolution to show the septum in cases of high insertion
of the ureter, which can be imaged with endoluminal sonography.
Retrograde ureteropyelography is used in all of our cases to visualize the
ureter and renal pelvis. Although it shows evidence of the course and caliber
of the ureter, this technique provides relatively little information regarding
the ureteropelvic junction itself because of the nature of anteroposterior
projection imaging. The imaging findings may suggest narrowing of the ureter,
but it is impossible to determine whether the narrowing is the result of
crossing vessels or is intrinsic. Similarly, a stream of contrast enhancement
along the peripheral margin, whether anterior, posterior, or medial, can
represent contrast material within the lumen of a highly inserting ureter or a
streaming effect resulting from a narrow segment. These configurations can be
detected only with the cross-sectional imaging of endoluminal sonography and
are best visualized on 3D presentations. In eight of 43 cases (18.6%) in this
study, endopy elotomy was obviated, and alternative management was chosen on
the basis of endoluminal sonographic findings alone.
Our preliminary study showed several advantages of 3D compared with 2D
imaging in the following aspects. First, 3D volume images can be viewed with a
standard anatomic orientation to obtain simultaneous display of the coronal,
oblique, and longitudinal planes, which is impossible with conventional 2D
imaging owing to scanning constraints. Second, rendering of the entire
structural volume depicts the continuity of the curved UPJ and ureter in a
long-axial single-image section. Third, precise visualization and
identification of irregularly shaped structures, such as crossing vessels and
septum, can be readily performed, which is useful for guiding interventional
procedures. Fourth, volume data can be archived and subsequently evaluated for
critical review and teaching.
Three-dimensional reconstruction of 2D sonographic images is a valuable
advance in the evolution of intraluminal imaging. It provides information
about the spatial relations of anatomic and pathologic structures that cannot
be evaluated with conventional methods. Although 2D imaging provides
information on anatomic structures, reconstruction into 3D format allows
better appreciation of anatomic and pathologic details. This capability
enhances the clinical applications in guiding and monitoring endourologic
interventional procedures.
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Abstract
Introduction
