Renal Pelvis and Ureter
Frances V. White
Peter A. Humphrey
I. NORMAL ANATOMY. The upper tract of the urinary collecting system is composed of the renal calyces, pelves, and ureters. Renal papillae protrude into the minor calyces, which expand into two or three major calyces, which in turn are outpouchings of the renal pelvis, a sac-like expansion of the upper ureter.
The mucosa is normally arranged in folds. The urothelium of the renal pelvis is three to five cell layers thick, and five to seven cell layers thick in the ureter. The lamina propria is composed of highly vascularized connective tissue without a muscularis mucosa; it is absent beneath the urothelium lining the renal papillae and is thinned along the minor calyces. The thickness and amount of muscularis propria in the collecting system within the renal sinus fat can be variable; ureteral muscularis propria is composed of interlacing bundles of smooth muscle, without inner or outer layers (Mills SE, ed. Histology for Pathologists. 2nd ed. Philadelphia: Lippincott Williams and Wilkins; 2007:839-907).
II. GROSS EXAMINATION AND TISSUE SAMPLING. Tissue samples include ureteroscopic biopsies, needle biopsies, pyeloplasty specimens, segmental ureterectomy specimens, radical cystectomy/cystoprostatectomy specimens, and radical nephroureterectomy with urinary bladder cuff resection specimens.
A. Ureteroscopic biopsies are entirely submitted. Because these are often minute in size, one approach to processing is to submit the biopsy sample for cytology cell block preparation (Urology. 1997;50:117).
B. Needle core biopsies of renal masses, including urothelial carcinoma involving the kidney, should be completely submitted. For microscopic examination, it is recommended that three levels on each of three hematoxylin and eosin (H&E)-stained slides be produced.
C. Pyeloplasty specimens for ureteropelvic junction obstruction consist of a portion of distal pelvis with a short segment of ureter attached to it. If the specimen is intact, it will be funnel-shaped, and narrowing, and/or angulation of the ureter may be evident. Usually, however, the specimen is longitudinally splayed open by the surgeon and consists of a flat, fan-shaped pelvis with nub of opened ureter at the “handle” of the fan. The mucosa should be examined to rule out rare mass lesions. Measurements include mural thickness of the pelvis and ureter, and both external and internal diameter of the ureter (the latter at its narrowest point). If present, narrowing and angulation of the ureter should be noted. Sections include serial cross sections of ureter and distal pelvis.
D. Segmental ureterectomy is performed for tumors of the proximal or mid-ureter. The length and diameter of the intact ureter is recorded, with a search for a mass by palpation and visual inspection. Proximal and distal cross-sectional margins are taken, and the outer aspect of the ureter is inked. The ureter is then opened longitudinally and assessed for mucosal abnormalities. After overnight fixation in 10% formalin, sections are taken to demonstrate the deepest invasion of any lesion(s). At least one section of uninvolved ureter should also be submitted.
E. Radical cystectomy/cystoprostatectomy with segment of ureters. Ureteral margin(s) may be submitted for frozen section for evaluation of carcinoma (and particularly carcinoma in situ). These are shaved margins and should be submitted as cross sections.
F. Radical nephroureterectomy with bladder cuff. Gross examination and sampling should document the relationship of tumor to adjacent renal parenchyma, peripelvic fat, nearest soft tissue margin, and ureter. Sections of grossly unremarkable kidney, pelvis, and ureter should be submitted. The important urothelial margin is the urinary bladder cuff, which can be sampled as shave sections.
III. DIAGNOSTIC FEATURES OF COMMON DISEASES
A. Benign conditions that involve the urothelium in the upper tract have an appearance similar to those in the urinary bladder. Examples are ureteritis (e-Fig. 21.1),* pyelitis cystica and glandularis, malakoplakia, nephrogenic adenoma, and squamous metaplasia (e-Fig. 21.2).
B. Ureteropelvic junction (UPJ) abnormalities can be seen in biopsies done for UPJ obstruction (UPJO), which is the most common cause of pediatric hydronephrosis and is usually diagnosed by fetal ultrasound. UPJO can also be seen in adults. Although in a minority of cases ureteropelvic junction obstruction is due to extrinsic compression by aberrant vessels, most cases are thought to be due to an “intrinsic” abnormality of the UPJ itself. The pathogenesis of intrinsic UPJO is not well established. Proposed etiologies include abnormal recanalization of the proximal ureter during embryogenesis, persistence of fetal mucosal folds, abnormalities of smooth muscle including disorientation and discontinuity, and abnormal innervation. UPJO initially results in pelvic and calyceal dilatation, followed by progressive obstructive renal damage which results in features of renal dysplasia in patients with end-stage disease. Gross and histopathologic findings reported in UPJO specimens include increased mural thickness, abnormal mucosal folds/fibroepithelial polyps, smooth muscle hypertrophy and disarray (e-Fig. 21.3), attenuation of smooth muscle with increased collagen to smooth muscle ratio, and chronic inflammation. Prognosis is based on concurrent renal biopsy and renal function rather than UPJ findings (Pediatr Nephrol. 2000;14:820, Pediatr Develop Pathol. 2006:9:72, Histopathology 2007;51: 709). Malignancy should also be excluded.
C. Benign epithelial neoplasms are rare and include urothelial papilloma, inverted papilloma, villous adenoma, and squamous papilloma.
D. Benign nonepithelial neoplasms include the distinctive fibroepithelial polyp, which is most frequently seen in the proximal ureter of young males. Microscopically, these are exophytic intraluminal projections of a variably inflamed fibrovascular stroma lined by a normal urothelium. Benign mesenchymal neoplasms such as leiomyoma, hemangioma, neurofibroma, and fibrous histiocytoma are rare.
E. Urothelial dysplasia in isolated form is rare and displays the same features as in the urinary bladder, where it is defined as low-grade intraurothelial neoplasia.
F. Renal pelvic and ureteral cancers are in the vast majority of cases, as in the urinary bladder, of urothelial type (Am J Surg Pathol. 2004;28:1545, Mod Pathol. 2006;19:494, Adv Anat Pathol. 2008;15:127).
Upper tract tumors differ from those in the urinary bladder in the following ways. Upper tract tumors are found at a lower frequency; have a stronger association with long-term analgesic (such as phenacetin) abuse and urinary tract obstruction; are associated with an increased frequency (in up to 65% of patients) of synchronous or metachronous urothelial neoplasms elsewhere in the urinary tract (Murphy WM, Grignon DJ, Perlman EJ. Tumors of the Kidney, Bladder, and Related Urinary Structures. Washington, DC: American Registry
of Pathology; 2004); and tend to present with higher histologic grade and at higher stage. Also, biopsy of upper tract tumors is more difficult than lower tract tumors. In about one of four cases, small ureteroscopic biopsies of the upper tract will be nondiagnostic due to inadequate tissue (Am J Surg Pathol. 2009;33:1540).
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