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Topic

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Renal pelvis

The renal pelvis is the funnel-shaped proximal part of the ureter that collects urine from the major calyces and directs it toward the ureteropelvic junction. It lies within the renal sinus, posterior to the renal vessels, and acts as the central collecting reservoir of the kidney. Its shape can be extrarenal (outside the hilum, large and distensible) or intrarenal (smaller, within the parenchyma).

The renal pelvis is clinically important in urology and radiology because it is the site of obstruction in hydronephrosis, calculi, and congenital anomalies such as ureteropelvic junction obstruction.

Synonyms

  • Pelvis renalis

  • Kidney pelvis

  • Renal collecting pelvis

Location and Structure

  • Located in the renal hilum within the renal sinus

  • Formed by the convergence of major calyces

  • Continues distally as the ureter at the ureteropelvic junction (UPJ)

  • Lined by urothelium (transitional epithelium) supported by a muscular wall that helps peristaltic urine flow

Relations

  • Anteriorly: Renal artery and vein at the hilum

  • Posteriorly: Renal sinus fat and part of renal parenchyma

  • Medially: Ureteropelvic junction

  • Laterally: Major calyces and renal parenchyma

Function

  • Acts as a reservoir to collect urine from the calyces

  • Directs urine flow into the ureter by passive drainage and active peristalsis

  • Serves as an anatomical landmark in imaging and surgical procedures of the kidney

Clinical Significance

  • Hydronephrosis: Dilatation of renal pelvis due to obstruction (stones, UPJ obstruction, tumors)

  • Urolithiasis: Stones frequently lodge at the renal pelvis or UPJ

  • Infection: Pyonephrosis can cause pus accumulation in the renal pelvis

  • Tumors: Transitional cell carcinoma may arise in renal pelvis

  • Surgical relevance: Landmark in pyeloplasty, nephrectomy, and endoscopic urology

MRI Appearance

T1-weighted images:

  • No fluid: Renal pelvis lumen appears dark (low signal) or collapsed

  • With simple fluid (urine): Low signal intensity

  • With blood/proteinaceous fluid: Bright or heterogeneous signal

  • Fat in renal sinus: Bright, helping delineate the pelvis

T2-weighted images:

  • No fluid: Thin dark outline of collapsed pelvis

  • With urine/fluid: Bright high signal intensity within the pelvis

  • With obstruction/hydronephrosis: Expanded, bright lumen with thin dark wall

  • Fat in sinus: Intermediate-to-bright signal

T1 Fat-Sat Post-Contrast:

  • Normal urothelium enhances faintly and uniformly

  • Tumors or inflammation show focal or irregular enhancement

  • Abscess or infection may show rim enhancement with central non-enhancing area

3D T2 SPACE / CISS:

  • Urine within the pelvis shows very bright signal

  • Pelvic wall appears as a thin low-signal rim

  • Excellent for demonstrating fine anatomy of the collecting system and small calculi/strictures

CT Appearance

Non-Contrast CT:

  • No fluid: Collapsed pelvis, not easily seen

  • With urine/fluid: Appears as low-density lumen within the renal sinus

  • Stones: Appear hyperdense within the renal pelvis

  • Fat in renal sinus: Seen as low attenuation, outlining pelvis

Post-Contrast CT (CT Urography):

  • Pelvis opacifies with contrast, appearing bright (high attenuation)

  • Obstruction shows delayed contrast filling or non-opacification

  • Tumors appear as irregular enhancing soft tissue masses within pelvis

  • Inflammation/infection shows wall thickening or rim enhancement

MRI images

Renal pelvis mri coronal anatomy image-img-00000-00000

CT images

Renal pelvis CT AXIAL anatomy image-img-00000-00000

CT images

Renal pelvis CT coronal anatomy image-img-00000-00000