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Cystic duct

The cystic duct is a short tubular structure that connects the gallbladder neck to the common hepatic duct, forming the common bile duct. Its length and course are variable, and it often contains mucosal folds known as the spiral valves of Heister, which help maintain patency.

The cystic duct is of great clinical and surgical importance because of its role in bile flow regulation and as a common site of obstruction by gallstones (leading to cholecystitis). It is also a critical structure identified during cholecystectomy.

Synonyms

  • Gallbladder duct

  • Ductus cysticus

  • Gallbladder outflow tract

Origin, Course, and Termination

  • Origin: Arises from the neck of the gallbladder

  • Course: Descends obliquely and medially through the hepatoduodenal ligament

    • Typically 2–4 cm long

    • Contains the spiral valves of Heister

    • Variable course: may join the common hepatic duct at different angles or levels

  • Termination: Joins the common hepatic duct to form the common bile duct

Relations

  • Anteriorly: Peritoneum of hepatoduodenal ligament

  • Posteriorly: Right hepatic artery branches

  • Medially: Common hepatic duct

  • Laterally: Gallbladder neck

  • Inferiorly: May lie close to the duodenum or pancreas in variant anatomy

Function

  • Provides a pathway for bile flow between gallbladder and extrahepatic bile ducts

  • Allows bile storage in the gallbladder and release into the CBD during digestion

  • Valves of Heister help regulate bile flow and prevent duct collapse

Clinical Significance

  • Gallstones (cystic duct obstruction): Most common cause of acute cholecystitis

  • Biliary colic: Transient blockage causes severe right upper quadrant pain

  • Mirizzi syndrome: Gallstone impacted in cystic duct compresses common hepatic duct

  • Surgical relevance: Must be clearly identified and ligated during cholecystectomy; misidentification is a major cause of bile duct injury

  • Imaging role: Evaluated by ultrasound, CT, MRCP, and intraoperative cholangiography

MRI Appearance

T1-weighted images:

  • Lumen: dark (low signal) due to bile fluid

  • Wall: thin and low signal, may enhance with contrast if inflamed

T2-weighted images:

  • Lumen: bright signal due to fluid

  • Wall: hypointense rim

  • Stones: dark filling defects within bright bile

STIR (Short Tau Inversion Recovery):

  • Lumen: bright signal

  • Surrounding fat suppressed (dark), improving duct visualization

  • Inflamed wall: hyperintense signal

T1 Fat-Sat Post-Contrast:

  • Normal wall: minimal enhancement

  • Cholecystitis/obstruction: wall thickening with avid enhancement

  • Abscess/infection: rim enhancement with central low signal

T2 Fat-Saturated HASTE:

  • Duct lumen: very bright signal

  • Useful for rapid detection of obstruction, strictures, or stones

  • Gallstones: dark signal voids against bright bile

T2 TSE Fat-Saturated 3D (MRCP):

  • Duct lumen: bright tubular structure

  • Excellent for 3D reconstruction of biliary anatomy

  • Detects strictures, variations, or stones

Thick-slab T2 Fat-Saturated HASTE:

  • Lumen: bright signal on projectional images

  • Quick overview of cystic duct anatomy and its junction with CHD

  • Stones/air: dark filling defects

CT Appearance

Non-Contrast CT:

  • Duct usually not well seen unless dilated

  • Stones may appear hyperdense if calcified

  • Surrounding fat planes visible

Post-Contrast CT:

  • Wall may enhance subtly

  • Dilatation appears as low-attenuation tubular structure

  • Inflammation: periductal fat stranding and enhancing walls

  • Stones without calcification often missed on CT

MRI image

Cystic duct mri axial cornal image-img-00000-00000

MRI image

Cystic duct mri axial anatomy image-img-00000-00000