1991, The British Journal of Radiology, 64, 898-900
Ultrasound diagnosis of horseshoe kidney By B. Banerjee, FRCS, D M R D , FRCR and I. Brett, D M R D , FRCR Department of Diagnostic Radiology, Tameside General Hospital, Ashton-Under-Lyne, Lancashire OL6 9RW, UK (Received January 1991 and in revised form March 1991) Keywords: Ultrasound, Horseshoe kidney, Renal outline, Inverted triangular or pyriform
Abstract. Ultrasound diagnosis of horseshoe kidneys depends on the demonstration of an isthmus or band of renal tissue across the midline of abdomen connecting the lower poles of the kidneys. In a number of cases this band of renal tissue may evade ultrasonic detection. In a series of 11 patients with horseshoe kidneys, sonographic detection of renal isthmus was achieved in seven patients, but in all 11 cases there was demonstrable alteration of renal outlines. Instead of normal reniform shape, the kidneys appeared "inverted pyriform" or "inverted triangular". Detection of such an altered renal outline should raise suspicion of horseshoe kidney.
Sonographic diagnosis of horseshoe kidney is based on the demonstration of the isthmus of renal tissue, situated in front of the great vessels in the midline of abdomen connecting the lower poles of the kidneys (Mindell & Kupic, 1977) (Fig. la & b). During sonographic screening of the renal tract in a child with recurrent urinary tract infection it was observed that the kidneys, when scanned along their long axes, appeared to be inverted triangular or inverted pyriform in shape, instead of the usual reniform or ovoid outline (Fig. 2). Although the significance of this was not recognized at the time, a similar sonographic appearance of kidneys was detected a few months later in an adult patient (Fig. 3a) and led to excretory urography, revealing a horseshoe anomaly of the kidneys (Fig. 3b). The authors wish to present the inverted triangular or inverted pyriform shape of the kidneys as an additional sonographic feature in the diagnosis of horseshoe kidneys. Materials and methods Over a period of 6 years, ultrasonic examination of 11 proven cases of horseshoe kidneys has been performed with real-time ultrasound units using 3.5 MHz and 5 MHz probes. In seven patients the initial diagnosis was made during excretory pyelography. Ultrasonic examinations of these patients were either carried out on the same day or they were recalled for sonography on a later date. In four patients, ultrasonography was the initial examination when the diagnosis of horseshoe kidneys was suspected, and was confirmed with excretory urography. Results
Ultrasound demonstrated the isthmus of renal tissue across the midline in seven cases. In three cases bowel Address correspondence to Dr B. Banerjee, Consultant Radiologist, Tameside General Hospital, Ashton-Under-Lyne, Lancashire OL6 9RW, UK.
gas or obesity prevented detection of midline structures and in one case, in spite of clear demonstration of midline structures, the isthmus could not be identified. In all cases while scanning along their long axes, both or at least one kidney was found to have inverted triangular or inverted pyriform outline. In one patient the right kidney was affected by hypernephroma but the left kidney, unaffected by tumour, appeared inverted pyriform in shape. Discussion
Horseshoe kidney is the commonest fusion anomaly of the renal tract, found in one of 425 autopsies (Pitts & Maecke, 1975). It has been found in association with other abnormalities of the urinary tract, such as infection, obstruction, and stone formation (Boatman et al, 1972). It is therefore important to make a positive diagnosis of this condition, which is easily diagnosed by excretory urography. In recent years and in many centres, sonography has replaced conventional excretory urography as the primary screening method. The isthmus of renal tissue connecting the lower poles of horseshoe kidney, on which diagnosis depends, may evade detection when the bridge of renal tissue is scant or replaced by a fibrous band (Sherwood, 1980) or obscured by overlying bowel gas (Hricak, 1987). It may be misdiagnosed as a lymph node or pancreatic mass (Mindell & Kupic, 1977). Although it is possible to infer the presence of horseshoe kidney by scanning the kidneys coronally and recognizing the medial deviation of the lower poles of the kidneys, even though the connecting bridge of renal tissue is not identified, considerable experience and meticulous scanning techniques are required. In all 11 patients in this series, either one or both kidneys demonstrated an inverted triangular or inverted pyriform shape. Detection of this altered renal shape should suggest horseshoe kidney. The midline of the abdomen in the vicinity of the lower poles of the kidneys should be meticulously scanned to detect the isthmus of The British Journal of Radiology, October 1991
Ultrasound diagnosis of horseshoe kidney
(a) (b) Figure 1. (a) Transverse ultrasound scan 6 cm above the umbilical plane, demonstrating renal isthmus (arrowed) connecting lower poles of kidneys across midline. Note that this renal isthmus can be mistaken for pancreatic tissue, (b) Longitudinal scan in the midline of upper abdomen demonstrating renal isthmus in cross section (white arrow heads) situated in front of the aorta. Note, aberrant artery to the renal isthmus originating from the aorta (curved white arrow). Also note, if only seen in the longitudinal plane, the renal isthmus may be mistaken for a lymph node.
(a) (b) Figure 2. Comparative sonographic appearances along the long axes of kidneys, (a) Reniform outline of a normal kidney, (b) Inverted triangular outline of the kidneys detected in the child.
(a) (b) Figure 3. (a) Inverted triangular shape of the kidney on ultrasound, (b) Excretory pyelography demonstrating the features of horseshoe kidneys. The band of renal tissue connecting the lower poles of the kidney is clearly outlined (arrow heads). The pelviureteric junctions are facing forwards instead of medially and the long axes of kidneys are vertical. Vol. 64, No. 766
899
I B. Banerjee and I. Brett renal tissue. If ultrasound fails to detect a renal isthmus, then an excretory urogram should be carried out to confirm or exclude diagnosis of horseshoe kidney. In conclusion, an inverted triangular or inverted pyriform shape of one or both kidneys has been consistently v , , •, , , 1 -j encountered on sonography with horseshoe kidney and should be considered a good indicator of this anomaly.
References BOATMAN, D. L., KOLIN, C. P. & FLOCKS, R. H., 1972. Congenital anomalies associated with horseshoe kidney. Joumal °f u™lo8y- ^07 205-207 HR CAK H I ' V I 987 " Renal ultrasound. In Diagnostic Ultrasound Text and Cases, ed. by D. A. Sarti (Year Book Medical Publishers Inc., Chicago), p. 353. M l N D E L L 5 H . J. & KUPIC, E. A., 1977. Horseshoe kidney: ultrasonic detection. American Journal of Roentgenology, 129, 526-527. PITTS, W. R. JR. & MAECKE, E. C , 1975. Horseshoe kidney: a
Acknowledgment Our thanks to Mrs B. Barker for preparation of the manuscript and Mr R. Biggs for photography.
900
40 year experience. Journal of Urology, 113, 743-746. SHERWOOD, T., 1980. The kidneys. In Uroradiology, ed by T. Sherwood, A. J. Davidson and L. B. Talner (Blackwell Scientific Publications, Oxford), p. 89.
The British Journal of Radiology, October 1991
Ultrasound diagnosis of horseshoe kidney By B. Banerjee, FRCS, D M R D , FRCR and I. Brett, D M R D , FRCR Department of Diagnostic Radiology, Tameside General Hospital, Ashton-Under-Lyne, Lancashire OL6 9RW, UK (Received January 1991 and in revised form March 1991) Keywords: Ultrasound, Horseshoe kidney, Renal outline, Inverted triangular or pyriform
Abstract. Ultrasound diagnosis of horseshoe kidneys depends on the demonstration of an isthmus or band of renal tissue across the midline of abdomen connecting the lower poles of the kidneys. In a number of cases this band of renal tissue may evade ultrasonic detection. In a series of 11 patients with horseshoe kidneys, sonographic detection of renal isthmus was achieved in seven patients, but in all 11 cases there was demonstrable alteration of renal outlines. Instead of normal reniform shape, the kidneys appeared "inverted pyriform" or "inverted triangular". Detection of such an altered renal outline should raise suspicion of horseshoe kidney.
Sonographic diagnosis of horseshoe kidney is based on the demonstration of the isthmus of renal tissue, situated in front of the great vessels in the midline of abdomen connecting the lower poles of the kidneys (Mindell & Kupic, 1977) (Fig. la & b). During sonographic screening of the renal tract in a child with recurrent urinary tract infection it was observed that the kidneys, when scanned along their long axes, appeared to be inverted triangular or inverted pyriform in shape, instead of the usual reniform or ovoid outline (Fig. 2). Although the significance of this was not recognized at the time, a similar sonographic appearance of kidneys was detected a few months later in an adult patient (Fig. 3a) and led to excretory urography, revealing a horseshoe anomaly of the kidneys (Fig. 3b). The authors wish to present the inverted triangular or inverted pyriform shape of the kidneys as an additional sonographic feature in the diagnosis of horseshoe kidneys. Materials and methods Over a period of 6 years, ultrasonic examination of 11 proven cases of horseshoe kidneys has been performed with real-time ultrasound units using 3.5 MHz and 5 MHz probes. In seven patients the initial diagnosis was made during excretory pyelography. Ultrasonic examinations of these patients were either carried out on the same day or they were recalled for sonography on a later date. In four patients, ultrasonography was the initial examination when the diagnosis of horseshoe kidneys was suspected, and was confirmed with excretory urography. Results
Ultrasound demonstrated the isthmus of renal tissue across the midline in seven cases. In three cases bowel Address correspondence to Dr B. Banerjee, Consultant Radiologist, Tameside General Hospital, Ashton-Under-Lyne, Lancashire OL6 9RW, UK.
gas or obesity prevented detection of midline structures and in one case, in spite of clear demonstration of midline structures, the isthmus could not be identified. In all cases while scanning along their long axes, both or at least one kidney was found to have inverted triangular or inverted pyriform outline. In one patient the right kidney was affected by hypernephroma but the left kidney, unaffected by tumour, appeared inverted pyriform in shape. Discussion
Horseshoe kidney is the commonest fusion anomaly of the renal tract, found in one of 425 autopsies (Pitts & Maecke, 1975). It has been found in association with other abnormalities of the urinary tract, such as infection, obstruction, and stone formation (Boatman et al, 1972). It is therefore important to make a positive diagnosis of this condition, which is easily diagnosed by excretory urography. In recent years and in many centres, sonography has replaced conventional excretory urography as the primary screening method. The isthmus of renal tissue connecting the lower poles of horseshoe kidney, on which diagnosis depends, may evade detection when the bridge of renal tissue is scant or replaced by a fibrous band (Sherwood, 1980) or obscured by overlying bowel gas (Hricak, 1987). It may be misdiagnosed as a lymph node or pancreatic mass (Mindell & Kupic, 1977). Although it is possible to infer the presence of horseshoe kidney by scanning the kidneys coronally and recognizing the medial deviation of the lower poles of the kidneys, even though the connecting bridge of renal tissue is not identified, considerable experience and meticulous scanning techniques are required. In all 11 patients in this series, either one or both kidneys demonstrated an inverted triangular or inverted pyriform shape. Detection of this altered renal shape should suggest horseshoe kidney. The midline of the abdomen in the vicinity of the lower poles of the kidneys should be meticulously scanned to detect the isthmus of The British Journal of Radiology, October 1991
Ultrasound diagnosis of horseshoe kidney
(a) (b) Figure 1. (a) Transverse ultrasound scan 6 cm above the umbilical plane, demonstrating renal isthmus (arrowed) connecting lower poles of kidneys across midline. Note that this renal isthmus can be mistaken for pancreatic tissue, (b) Longitudinal scan in the midline of upper abdomen demonstrating renal isthmus in cross section (white arrow heads) situated in front of the aorta. Note, aberrant artery to the renal isthmus originating from the aorta (curved white arrow). Also note, if only seen in the longitudinal plane, the renal isthmus may be mistaken for a lymph node.
(a) (b) Figure 2. Comparative sonographic appearances along the long axes of kidneys, (a) Reniform outline of a normal kidney, (b) Inverted triangular outline of the kidneys detected in the child.
(a) (b) Figure 3. (a) Inverted triangular shape of the kidney on ultrasound, (b) Excretory pyelography demonstrating the features of horseshoe kidneys. The band of renal tissue connecting the lower poles of the kidney is clearly outlined (arrow heads). The pelviureteric junctions are facing forwards instead of medially and the long axes of kidneys are vertical. Vol. 64, No. 766
899
I B. Banerjee and I. Brett renal tissue. If ultrasound fails to detect a renal isthmus, then an excretory urogram should be carried out to confirm or exclude diagnosis of horseshoe kidney. In conclusion, an inverted triangular or inverted pyriform shape of one or both kidneys has been consistently v , , •, , , 1 -j encountered on sonography with horseshoe kidney and should be considered a good indicator of this anomaly.
References BOATMAN, D. L., KOLIN, C. P. & FLOCKS, R. H., 1972. Congenital anomalies associated with horseshoe kidney. Joumal °f u™lo8y- ^07 205-207 HR CAK H I ' V I 987 " Renal ultrasound. In Diagnostic Ultrasound Text and Cases, ed. by D. A. Sarti (Year Book Medical Publishers Inc., Chicago), p. 353. M l N D E L L 5 H . J. & KUPIC, E. A., 1977. Horseshoe kidney: ultrasonic detection. American Journal of Roentgenology, 129, 526-527. PITTS, W. R. JR. & MAECKE, E. C , 1975. Horseshoe kidney: a
Acknowledgment Our thanks to Mrs B. Barker for preparation of the manuscript and Mr R. Biggs for photography.
900
40 year experience. Journal of Urology, 113, 743-746. SHERWOOD, T., 1980. The kidneys. In Uroradiology, ed by T. Sherwood, A. J. Davidson and L. B. Talner (Blackwell Scientific Publications, Oxford), p. 89.
The British Journal of Radiology, October 1991
