Renal Agenesis and Ectopia

Agenesis or ectopia of the kidney is frequently accompanied by characteristic malposition of specific portions of the bowel.16 Particular segments of the intestine may occupy the area of the renal fossa on the side of agenesis or ectopia, or show characteristic displacement and extrinsic mass effect by an ectopic kidney in as many as 75% of the cases.16,17

The clinical value of these observations is twofold:

1. Identification of the characteristic intestinal malposition or displacement on a barium contrast study uncovers the renal anomaly, which may have multiple clinical implications.

These observations not only allow one to suspect congenital renal anomalies during barium enema examinations, but help in assessment of the nature of the renal abnormality when excretory urography reveals an apparently solitary kidney. In the pediatric patient, they may be particularly helpful in the differential diagnosis between renal agenesis and multicystic dysplastic kid-ney.18 Although the ureter and trigone are absent in 80% of cases of agenesis,19,20 one-third of cases of multicystic dysplastic kidney also have no demonstrable ureter or trigone at cystoscopy.19 Several observers have concluded that nonvisualization of the kidney on excretory urography with normal position of the colon excludes agenesis or ectopia as diagnostic considerations.18,21

Fig. 9-32. Colonic changes secondary to left perinephritis.

Lateral radiograph (a) and frontal spot film (b) of a barium enema study demonstrate persistent irregular narrowing 5 cm in length (arrows) just distal to the splenic flexure. The mucosal folds are intact, and there is no significant obstruction. Attention was then directed toward the left kidney, and a radiologic workup revealed three 5 x 4 cm perirenal abscesses. At nephrectomy, the lateral surfaces of the masses were adherent to the descending colon. (Reproduced from Meyers. )

Fig. 9-32. Colonic changes secondary to left perinephritis.

Lateral radiograph (a) and frontal spot film (b) of a barium enema study demonstrate persistent irregular narrowing 5 cm in length (arrows) just distal to the splenic flexure. The mucosal folds are intact, and there is no significant obstruction. Attention was then directed toward the left kidney, and a radiologic workup revealed three 5 x 4 cm perirenal abscesses. At nephrectomy, the lateral surfaces of the masses were adherent to the descending colon. (Reproduced from Meyers. )

2. Such bowel changes should not be mistaken for a form of internal hernia, abnormality of rotation of the intestines, or displacement by a tumor mass or organ-omegaly.

Embryologic Considerations. Ashley and Mostofi19 believe that the initiating factor in renal agenesis is in the metanephric blastema. Disturbances of embryologic growth from the fourth to the eighth week of fetal life may result in renal ectopia. Normally, the kidney reaches its mature level opposite the second lumbar vertebra at the end of the second month. During their migration, the kidneys also rotate 90° so that their convex borders, originally directed dorsally, become directed laterally.

The normal developmental ascent of the kidneys is necessary for the formation of the extraperitoneal perirenal fascial planes.16'20'22 With either agenesis or ectopia of the kidney, extraperitoneal connective tissue in the flanks fails to condense into well-defined fascial layers. In contrast, the perirenal fascia is present in cases ofpto-tic kidney.

Figure 9-41 is an anatomic cross-section through an ectopic kidney in the pelvis. While the usual perirenal fascial layers immediately enveloping it are clearly demarcated, these could not be identified in the upper extraperitoneal space on the same side; they were present on the opposite side where the kidney was normally positioned. I have documented these associated features text continues on page 519

Left Renal Agenesis

Fig. 9—33. Colonic changes secondary to left perinephritis.

(a) Barium enema study reveals localized rigidity and scalloping along the medial wall of the mid-descending colon. A left renal calculus is evident.

(b) Selective renal arteriography documented changes of xanthogranulomatous pyelonephritis. On nephrogram phase, wide displacement of the capsular artery (arrows) indicates a diffuse perirenal abscess. This was confirmed at nephrectomy, which also revealed the inflammatory process adhering to the medial wall of the descending colon. K = kidney.

(Reproduced from Meyers. )

Fig. 9—33. Colonic changes secondary to left perinephritis.

(a) Barium enema study reveals localized rigidity and scalloping along the medial wall of the mid-descending colon. A left renal calculus is evident.

(b) Selective renal arteriography documented changes of xanthogranulomatous pyelonephritis. On nephrogram phase, wide displacement of the capsular artery (arrows) indicates a diffuse perirenal abscess. This was confirmed at nephrectomy, which also revealed the inflammatory process adhering to the medial wall of the descending colon. K = kidney.

(Reproduced from Meyers. )

Fig. 9—34. Colonic changes secondary to left perinephritis.

Barium enema study shows displacement and mucosal fixation (arrows) along the medial wall of the descending colon. Staghorn calculi are evident in the left kidney. The colonic changes are secondary to a large peripheral abscess which required drainage.

Fig. 9—35. Colonic changes secondary to right perinephritis.

(a and b) Barium enema study shows mass displacement and inflammatory mucosal thickening of the ascending colon.

(c) Intravenous urography demonstrates no function in an enlarged right kidney containing an opaque calculus.

Nephrectomy confirmed the presence of xanthogranulomatous pyelonephritis with a perirenal abscess adherent to the ascending colon.

Fig. 9—35. Colonic changes secondary to right perinephritis.

(a and b) Barium enema study shows mass displacement and inflammatory mucosal thickening of the ascending colon.

(c) Intravenous urography demonstrates no function in an enlarged right kidney containing an opaque calculus.

Nephrectomy confirmed the presence of xanthogranulomatous pyelonephritis with a perirenal abscess adherent to the ascending colon.

Fig. 9—36. Renointestinal fistula secondary to right perinephritis.

(a) Barium enema study shows loculated extravasation from the distal ascending colon, which also presents a stricture with intact mucosal folds.

(b) Excretory urography demonstrates no function on the right. Distortion of the colonic gas shadow with faint extraluminal gas collections are apparent.

A perirenal abscess secondary to xanthogranulomatous pyelonephritis had established a fistulous communication with the colon.

Fig. 9—36. Renointestinal fistula secondary to right perinephritis.

(a) Barium enema study shows loculated extravasation from the distal ascending colon, which also presents a stricture with intact mucosal folds.

(b) Excretory urography demonstrates no function on the right. Distortion of the colonic gas shadow with faint extraluminal gas collections are apparent.

A perirenal abscess secondary to xanthogranulomatous pyelonephritis had established a fistulous communication with the colon.

Shadow Kidney

Fig. 9—37. Renocolic fistula secondary to left perinephritis.

(a) Unenhanced CT shows dilatation of the collecting system (K) and the pelvis (P) of the left kidney. Inflammatory changes (straight arrows) abut the collapsed descending colon (curved arrow).

(b) CT with intravenous contrast 1 week later demonstrates a fluid-gas level in an obstructed and thick-walled renal pelvis (P). Perirenal abscess (black arrows) is adherent to the posterior wall of the descending colon (curved arrow), proved to be the site of two renocolic fistulas.

(Reproduced from Parvey et al.10)

Fig. 9—38. Renocolic fistula secondary to xanthogranulomatous pyelonephritis with perirenal abscess.

(a and b) CT without intravenous contrast shows bilateral staghorn calculi (arrowheads) and hypodense areas within the left kidney representing xanthogranulomatous pyelonephritis. Inflammatory changes and a large perirenal abscess (A) extend into the lateral abdominal wall near the descending colon (C). (c) Antegrade contrast study via nephrostomy tube (arrows) demonstrates fistulous communication from the collecting system of the left kidney (K) into the descending colon (C). Intravenous urog-raphy showed a nonfunctioning left kidney. (Reproduced from Parvey et al.lQ)

Perirenal Abscess Ectopia Renal

Fig. 9—39. Renocolic fistula secondary to pyelonephritis and perirenal abscess.

(a) CT with intravenous contrast shows a large perirenal abscess (A) that abuts the descending colon (arrows). K = kidney.

(b) CT after contrast injection into the perirenal drainage catheter discloses contrast extending from the left perirenal space (arrow) into the descending and sigmoid colon (arrowhead).

(Reproduced from Parvey et al.10)

Fig. 9—39. Renocolic fistula secondary to pyelonephritis and perirenal abscess.

(a) CT with intravenous contrast shows a large perirenal abscess (A) that abuts the descending colon (arrows). K = kidney.

(b) CT after contrast injection into the perirenal drainage catheter discloses contrast extending from the left perirenal space (arrow) into the descending and sigmoid colon (arrowhead).

(Reproduced from Parvey et al.10)

Upper Gastric Ulcer

Fig. 9—40. Renogastric fistula secondary to gastric ulcer.

(a) Excretory urogram. Gross chronic inflammatory changes with distorted collecting system on the left.

(b) Retrograde pyelogram. Loculated extravasation (arrow) with opacification of gastric mucosa (arrowheads).

(c and d) Upper gastrointestinal series documents large ulcer on posterior wall of stomach (arrows) penetrating to the left kidney. (Reproduced from Meyers. )

Fig. 9—40. Renogastric fistula secondary to gastric ulcer.

(a) Excretory urogram. Gross chronic inflammatory changes with distorted collecting system on the left.

(b) Retrograde pyelogram. Loculated extravasation (arrow) with opacification of gastric mucosa (arrowheads).

(c and d) Upper gastrointestinal series documents large ulcer on posterior wall of stomach (arrows) penetrating to the left kidney. (Reproduced from Meyers. )

Renal Crest

Fig. 9—41. Anatomic cross-section through pelvis at the level of the iliac crest.

An ectopic right kidney (K), deriving its blood supply (arrows) from the lower abdominal aorta, maintains its investment by well-defined extraperitoneal fascial planes (arrowheads). These layers of perirenal fascia are not developed cephalad to the ectopic kidney, where only pliable fat constitutes the extraperitoneal tissues. (Reproduced from Meyers et al.16)

Fig. 9—41. Anatomic cross-section through pelvis at the level of the iliac crest.

An ectopic right kidney (K), deriving its blood supply (arrows) from the lower abdominal aorta, maintains its investment by well-defined extraperitoneal fascial planes (arrowheads). These layers of perirenal fascia are not developed cephalad to the ectopic kidney, where only pliable fat constitutes the extraperitoneal tissues. (Reproduced from Meyers et al.16)

in vivo by computed tomography. Similarly, cases of renal agenesis and crossed fused ectopia studied by retroper-itoneal pneumography document failure of the perirenal fascia to form on the side of the absent kidney (Figs. 942 and 9-43).

The lack of restraining fascia appears to contribute to the ease with which bowel malpositions itself into the pliable extraperitoneal fat in the "empty" renal fossa. The associated findings strongly suggest that development ofnot only the extraperitoneal perirenal fascia, but also portions of the intestinal mesenteric fixation, are embryologically dependent on normal ascent of the kid-ney.16

Incidence. These anomalies are not rare. Unilateral renal agenesis and renal ectopia have been found more frequently on radiographic examination (1 in 500) than in autopsy series (1 in 700 to 1500).

19,23,24

The incidence of crossed fused ectopia is only 1 in 7500. An over-representation may be assumed in urologic cases because pathologic conditions, such as stone formation or hydronephrosis, are more common. There is a male-to-female preponderance in a ratio of 3:2, and the anom-

19 20 25

alies are more common on the left side.

Complications and Associated Anomalies. While such renal anomalies may be compatible with a long life, the incidence of renal disease in a congenitally solitary kidney as a cause of death is high.19 In unilateral agenesis, the opposite kidney has been found to be diseased in one-third25 to almost two-thirds26 of the cases, usually secondary to chronic pyelonephritis. Compensatory hypertrophy of the solitary kidney results in a palpable mass in the flank about 25% of the time.26 Furthermore, because it projects below the rib cage, it is more susceptible to injury.

Unilateral Renal Agenesis

Fig. 9-42. Unilateral left renal agenesis.

Presacral retroperitoneal pneumography demonstrates that none of the perirenal fascial layers has developed on the affected side.

(Reproduced from Meyers et al.16)

Fig. 9-42. Unilateral left renal agenesis.

Presacral retroperitoneal pneumography demonstrates that none of the perirenal fascial layers has developed on the affected side.

(Reproduced from Meyers et al.16)

In an ectopic kidney or crossed renal ectopia with fusion, the incidence of complications such as lithiasis, infection, and hydronephrosis also approaches 50%.27 Pain in the lower abdomen may lead to such erroneous diagnoses as appendicitis, diverticulitis, neoplasm of the colon, mesenteric cyst, and ovarian disease.

Pelvic and horseshoe kidneys are prone to injury from any mechanism that compresses the kidney against the spine or sacrum, as in seatbelt injuries.28

Pelvic ectopy is important in obstetrics because it may complicate delivery. In a review of the subject, Anderson and associates concluded that most women with pelvic kidney may be delivered vaginally, but if all of the renal tissue lies in the pelvis, as in bilateral ectopy or solitary fused pelvic kidney, cesarean section is the best method of delivery.29

Hiroshima Victims Vaporized

Fig. 9-43. Crossed renal ectopia with fusion.

Presacral retroperitoneal pneumogram with excretory urography. While the adrenal glands (A) have developed normally, the extraperitoneal fat has failed to condense into well-defined connective tissue fascial layers on the left, opposite the fused kidneys (K). (Reproduced from Meyers et al.l6)

Fig. 9-43. Crossed renal ectopia with fusion.

Presacral retroperitoneal pneumogram with excretory urography. While the adrenal glands (A) have developed normally, the extraperitoneal fat has failed to condense into well-defined connective tissue fascial layers on the left, opposite the fused kidneys (K). (Reproduced from Meyers et al.l6)

Anomalies of structures arising from the urogenital ridge are associated with these renal conditions in as many as 18.5% of cases.19,25,27,30-32These include vaginal atresia; hypoplastic, unicornuate, or didelphys uterus (Fig. 9-44); and the absence of an ovary. Less often, monoorchidism and abnormality of the vas deferens are seen in males. The Mullerian duct system develops at a later stage in embryogenesis than the Wolffian duct and is therefore more likely to undergo malformation, which has been postulated to account for the higher incidence of associated genital anomalies in females than males.

The ipsilateral adrenal gland is often identified on CT as a disk-shaped organ with a parasagittal orientation that appears linear on cross-section.17,33 (Figs. 9-44c and 9-45). Presumably, this results from the absence of a normally located kidney, which exerts a mass effect on the large, globular fetal adrenal before it shrinks.

Extragenitourinary tract anomalies are frequently associated with unilateral renal agenesis in children25,34

Unilateral Renal Agenesis Xray

Fig. 9—44. Renal agenesis associated with uterus didelphys.

(a) Axial T2-weighted MR image in a 12-year-old girl demonstrates uterus didelphys and duplicated upper vagina with left sided hematometra (M) and hematocolpos (C),

(b) Intravenous urography and (c) coronal T2-weighted image of the upper abdomen demonstrate a kidney only on the right. It is hypertrophied, and the renal axis shows slight clockwise rotation. In c, note malposition of bowel in the "empty" renal fossa and a linear configuration of the left adrenal gland.

(Reproduced from Tanaka et al. )

Fig. 9—44. Renal agenesis associated with uterus didelphys.

(a) Axial T2-weighted MR image in a 12-year-old girl demonstrates uterus didelphys and duplicated upper vagina with left sided hematometra (M) and hematocolpos (C),

(b) Intravenous urography and (c) coronal T2-weighted image of the upper abdomen demonstrate a kidney only on the right. It is hypertrophied, and the renal axis shows slight clockwise rotation. In c, note malposition of bowel in the "empty" renal fossa and a linear configuration of the left adrenal gland.

(Reproduced from Tanaka et al. )

Pancake Adrenal Gland Renal Agenesis

Fig. 9—45. Colonic malposition in left renal agenesis.

CT demonstrates deflection of the colon deeply within the "empty" renal fossa medial to the spleen. Note the elongated linear configuration of the left adrenal gland

Pneumatosis

Fig. 9—46. Renal agenesis in association with congenital scoliosis.

This child presented with congenital scoliosis of the lumbar spine with anomalies, including butterfly vertebrae. Intravenous urography demonstrates absence of the right kidney and compensatory hypertrophy on the left.

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