15.2 Genitourinary, Biliary & Special Fluoroscopic Studies (IVU, Cystography, ERCP, Myelography)

15.2 Genitourinary, Biliary & Special Fluoroscopic Studies

Specialized fluoroscopic and contrast procedures evaluate non-vascular internal organs, specialized ductal networks, and the central nervous system. Mastery of Intravenous Urography (IVU), Voiding Cystourethrography (VCUG), Endoscopic Retrograde Cholangiopancreatography (ERCP), and Myelography is essential for radiologic technology practice and board examination excellence.

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1. Intravenous Urography (IVU / IVP)

Intravenous Urography (historically termed Intravenous Pyelography or IVP) is a functional radiographic examination of the urinary system. It evaluates the renal parenchyma, calyces, renal pelvis, ureters, and urinary bladder following intravenous administration of an iodinated contrast agent.

Indications, Patient Preparation, & Biochemical Screening

• Clinical Indications: Urolithiasis (kidney stones), hematuria, hydronephrosis, renal pyelonephritis, renal masses, and flank pain.
• Preparation: NPO after midnight (8 hours) and bowel cleansing to eliminate gas and fecal shadows over the kidneys.
• Laboratory Screening: Kidney function must be evaluated prior to injecting contrast to avoid Contrast-Induced Nephropathy (CIN):
  • Blood Urea Nitrogen (BUN): Normal range is 7 to 20 mg/dL.
  • Serum Creatinine: Normal range is 0.6 to 1.2 mg/dL (levels $> 1.5 \ ext{ mg/dL}$ indicate renal impairment).
  • Estimated Glomerular Filtration Rate (eGFR): Normal is $> 60 \ ext{ mL/min/1.73 m}^2$ (values $< 30 \ ext{ mL/min/1.73 m}^2$ represent severe renal failure and are relative contraindications for iodinated contrast).

Imaging Sequence & Timing Protocol

1. Scout Radiograph (KUB):
   • Taken prior to contrast injection. Verifies technical factors, patient preparation, anatomical borders (T12 to pubic symphysis), and detects calcified renal calculi or vascular calcifications.
2. Nephrogram / Nephrotomogram Phase (1 to 3 Minutes Post-Injection):
   • Physiologic Stage: Captures the initial nephron uptake and parenchymal "blush" of the kidney cortex and medulla before contrast filters into the collecting system.
   • Tomographic Cuts: Linear blurs remove bowel gas superimposition over the renal outlines.
3. 5-Minute & 10-Minute Excretory Radiographs:
   • Demonstrates early filling of the minor calyces, major calyces, renal pelvis, and upper ureters.
4. 30° RPO and LPO Oblique Radiographs (15 Minutes):
   • Mechanical Principle of 30° Body Rotation:
     • Rotating the patient 30° elevates one kidney parallel to the Image Receptor (IR) while placing the opposite downside kidney perpendicular to the IR.
     • The upside (elevated) kidney lies parallel to the IR, providing a true anatomical profile of the renal parenchyma.
     • The downside kidney is perpendicular, projecting its downside ureter clear of the transverse processes and vertebral column.
   • Positioning Rule Summary:
     • 30° RPO: Demonstrates the Left Kidney parallel to the IR and the Right Ureter unsuperimposed.
     • 30° LPO: Demonstrates the Right Kidney parallel to the IR and the Left Ureter unsuperimposed.
5. Post-Void KUB:
   • Taken immediately after the patient voids. Assesses bladder emptying efficiency, residual urine volume, small mucosal tumors, or prostate enlargement in male patients.

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2. Retrograde Pyelography & Voiding Cystourethrography (VCUG)

Retrograde Pyelography

• Procedure Nature: A non-functional diagnostic procedure performed under aseptic surgical conditions in an operating room suite by a urologist using a cystoscope.
• Method: Ureteral catheters are inserted through the bladder into the orifice of the ureters under cystoscopic guidance. Water-soluble contrast is injected directly upward into the renal pelvis and calyces.
• Primary Advantage: Because contrast is introduced locally without intravascular injection, renal function is not required, making this procedure safe for patients with renal failure or severe contrast allergy history.

Voiding Cystourethrography (VCUG)

• Clinical Indications: Vesicoureteral reflux (VUR - abnormal backflow of urine from the bladder into the ureters), recurrent pediatric urinary tract infections (UTIs), anatomical bladder outlet obstructions, and urethral strictures.
• Procedural Steps:
  1. A preliminary scout image is acquired.
  2. Under sterile technique, a urethral catheter is passed into the bladder.
  3. Contrast medium is instilled gravity-drip into the bladder until full capacity is reached.
  4. The catheter is removed, and dynamic fluoroscopic images are acquired while the patient voids on the footstand of the fluoroscopic tilt table.
• Male Positioning for VCUG:
  • The male patient is rotated into a 30° Right Anterior Oblique (RAO) or Right Posterior Oblique (RPO) position during active voiding.
  • Diagnostic Purpose: The 30° oblique posture projects the entire length of the male urethra (prostatic, membranous, and penile urethra) over the soft tissues of the right thigh, completely free of bony superimposition from the pubis and femur.

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3. Endoscopic Retrograde Cholangiopancreatography (ERCP)

ERCP is a specialized diagnostic and therapeutic procedure that combines high-resolution fiberoptic endoscopy with dynamic fluoroscopy to visualize the biliary tree and pancreatic ducts.

Clinical Indications

Investigates obstructive jaundice, choledocholithiasis (gallstones lodged in the common bile duct), biliary ductal strictures, pancreatic duct anomalies, and chronic pancreatitis.

Anatomy & Procedural Technique

1. A gastroenterologist passes a side-viewing fiberoptic duodenoscope down through the esophagus, stomach, and descending duodenum.
2. The scope locates the Ampulla of Vater (Hepatopancreatic Ampulla) on the medial duodenal wall.
3. A small cannula is advanced through the scope into the Sphincter of Oddi and inserted selectively into the common bile duct or pancreatic duct.
4. Water-soluble iodinated contrast is injected into the ductal system under fluoroscopic monitoring while the radiologic technologist acquires spot images.
5. Therapeutic Interventions: Sphincterotomy (cutting the sphincter muscle), balloon dilation of duct strictures, mechanical stone extraction using retrieval baskets, and biliary stent placement.

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4. Myelography

Myelography is the radiographic examination of the spinal cord, nerve roots, and surrounding meningeal structures following intrathecal administration of contrast into the subarachnoid space.

Clinical Indications

Demonstrates herniated nucleus pulposus (HNP), spinal canal stenosis, spondylolisthesis, extradural mass lesions, spinal cord tumors, and post-traumatic nerve root avulsions.

Contrast Selection Rules

• Mandatory Contrast: Non-ionic, water-soluble, low-osmolality iodinated contrast media (e.g., Isovue-M or Omnipaque) engineered specifically for intrathecal application.
• CRITICAL CONTRAINDICATION: Ionic contrast media and oil-based contrast media (Pantopaque) must NEVER be injected into the subarachnoid space. Ionic agents break down into charged ions in the cerebrospinal fluid (CSF), inducing fatal neurotoxicity, severe cerebral convulsions, and arachnoiditis.

Puncture Sites & Technical Execution

1. Lumbar Puncture Site (L3–L4):
   • The safest and most common access site. Interspace L3–L4 lies well below the conus medullaris (the terminal tapered tip of the spinal cord), which terminates at the level of L1–L2 in adults, preventing needle trauma to the cord.
2. Cervical Puncture Site (C1–C2):
   • Performed under lateral fluoroscopy at the C1–C2 level when the lumbar region is completely obstructed by mass lesions or severe spinal stenosis.

Patient Positioning & Gravity Contrast Control

• Subarachnoid Injection: CSF is sampled for laboratory analysis, followed by slow intrathecal injection of non-ionic contrast.
• Tilt-Table Fluoroscopy: The fluoroscopic table is tilted head-down (Trendelenburg) or foot-down to glide the contrast column along the subarachnoid space using gravity.
• Prevention of Basilar Contrast Migration: When tilting the patient into Trendelenburg to image the cervical spine, the patient's neck must be kept in hyper-extension. Hyper-extension compresses the posterior subarachnoid space at the cisterna magna, preventing contrast from flowing upward into the cerebral ventricles and cranial vault, which causes severe post-lumbar-puncture headaches.
• Post-Procedure Care: Patient must remain elevated at 30° to 45° for 4 to 8 hours post-procedure to facilitate gradual contrast absorption and reduce severe headache risk.

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Summary Table: Genitourinary, Biliary & Special Fluoroscopic Studies