Porta Hepatis: Anatomy and Imaging

• The porta hepatis encompasses the portal triad (main portal vein, common hepatic artery, and common bile ducts), lymphatics, nerves, and connective tissue.
• Major vascular diseases of the portal triad include thrombosis, stenosis, and aneurysm.
• Hepatic artery thrombosis and stenosis require immediate attention to reduce graft loss in liver transplant recipients.
• The hepatoduodenal ligament serves as a route for the spread of pancreatic and gastrointestinal cancers.
• Ultrasonography (US) demonstrates anatomic variations and pathologic conditions, also initial modality for vascular and biliary lesions.
• Multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) allow characterization and differentiation of masses.
• Imaging-guided interventions, like embolization and stent placement, play a role in disease management.
• Imaging of the porta hepatis region is both challenging and critical because of its complex anatomic architecture.

Radiologic Anatomy

• The Porta Hepatis, or hilum of the liver, is a deep, short, transverse fissure across the left posterior aspect of the undersurface of the right lobe.
• It transmits the portal triad, nerves, and lymphatics; the portal vein, proper hepatic artery, and nerves ascend, while the common bile duct and lymphatics descend.
• All structures are enveloped by the lesser omentum or hepatoduodenal ligament, loose areolar tissue, and the fibrous capsule of Glisson.
• The ligament also envelops the gallbladder neck and cystic duct, inserting between the duodenum's first and second portions.
• The common bile duct and proper hepatic artery are located anterior to the portal vein.
• The proper hepatic artery branches into the right and left hepatic arteries.
• Lymphatics drain the liver, gallbladder, bile ducts, duodenum, stomach, and pancreas into paraaortic nodes.
• Nerves are branches of the left vagus nerve and sympathetic branches of the celiac plexus.

Imaging Modalities for Evaluation

• Ultrasonography (US) is inexpensive and widely used.
• High-resolution transducers have increased US sensitivity.
• Color, spectral, and power Doppler US provide information about the vascular structures.
• Advances like 3D US and US contrast agents enhance US utility.
• MDCT is the modality of choice for comprehensive evaluation.
• Multiphasic image acquisition (unenhanced, arterial, venous, delayed) assesses enhancement characteristics.
• The normal portal vein enhances uniformly in the portal venous phase, with a diameter of 11-13 mm.
• The hepatic artery: arterial phase (20-25 seconds post-contrast) with MDCT angiography.
• Multiplanar reformations and post-processing increase diagnostic accuracy, but MDCT limitations include radiation exposure and contrast media nephrotoxicity.
• Bile: high signal intensity on MR images.

Spectrum of Vascular and Nonvascular Diseases

• Classification of diseases affecting the porta hepatis includes vascular and nonvascular conditions.
• Vascular diseases affect the main portal vein and common hepatic artery.
• Nonvascular diseases affect the biliary tree, lymphatics, nerves, and connective tissue.

Diseases of the Portal Vein

• Portal vein thrombosis is seen in various pathologic conditions, including cirrhosis, cholangitis, pancreatitis, appendicitis, diverticulitis, and neoplasms.
• Bland portal vein thrombosis occurs in 11.2%-15.8% of cases of cirrhosis
• Hepatocellular carcinoma can invade, resulting in malignant portal vein thrombosis in up to 44% of cases.
• The disease course with respect to thrombosis depends on the extent, collateralization, and duration.
• Acute thrombosis can be asymptomatic or cause variceal bleeding and shock.
• Chronic thrombosis associates with splenomegaly, gastroesophageal varices, ascites, and chronic gastrointestinal bleeding.
• "Cavernous transformation": multiple tortuous venous collaterals replace the occluded portal vein (as early as 20 days post-thrombosis).
• US depicts acute thrombosis as a dilated portal vein with absence of flow, and subacute and chronic thrombus is echogenic.
• Color Doppler US allows real-time evaluation.
• Important: differentiate sluggish flow (severe portal hypertension) from portal vein thrombosis.
• Prominent hepatic artery inflow: indirect sign of portal vein thrombosis.
• Malignant portal vein thrombosis is characterized by expansile dilatation of the portal vein and demonstrates intermediate to high signal intensity on T2-weighted images.
• Lack of flow demonstrated on color Doppler US images and dynamic contrast enhanced studies with MDCT/MRI

Portal Vein Stenosis

• Stenosis is a recognized complication of liver transplantation and other surgeries; can result in massive ascites.
• Caused by locally recurrent periampullary cancers
• Diagnosis: spectral Doppler US (three- to fourfold velocity gradient across the portal vein anastomosis) with color Doppler demonstrating focal aliasing, with increase number and size of collaterals on ultrasound
• Symptomatic cases may necessitate balloon angioplasty or stent placement (10,12).

Portal Vein Aneurysm

• Aneurysms in the portal venous system account for only 3% of all venous aneurysms; prevalence = 0.6-4.3 per 1000 patients.
• The most common site of aneurysm is the main portal vein
• Etiopathogenesis includes congenital causes, vessel wall weakness, and anomalous portal vein branching.
• Diagnosed with US, MDCT, and MR imaging when the portal vein diameter exceeds 20 mm
• Complications: portal hypertension, thrombosis, venous rupture, and biliary obstruction (8)
• Treatment: includes anticoagulation therapy, percutaneous thrombolysis, or thrombectomy; therapeutic surgical options = portocaval shunts and aneurysmorrhaphy (16).

Portal Vein Gas

• With increasing MDCT use, recognized early; mesenteric ischemia mortality rates range from 29% to 43%.
• Causes: Intra-abdominal abscesses, diverticulitis, inflammatory bowel disease, and necrotizing pancreatitis
• Portal Vein gas appears on abdominal radiographs as linear lucent shadows and US displays reverberation.
• Management requires detection of the underlying cause.
• Necessary: Surgical Intervention with cases of mesenteric ischemia, diverticulitis, and bowel obstruction.
• Cases of trauma, colonoscopy, or idiopathic causes are managed with conservative management

Common Hepatic Artery Thrombosis and Stenosis

• Thrombosis is a leading cause of morbidity and mortality after orthotopic liver transplantation, with a mortality rate of about 33%, and over 80% mortality in undiagnosed cases.
• Dx: Made with color. Pulsed Doppler US findings of lack of flow in the hepatic artery. Although Doppler US is used, it is highly operator dependent. Contrast enahnced US has also been used.
• Findings in MDCT include an abrupt cut off the hepatic artery at the anastomotic site; and the nonenhancement of the hepatic artery
• Treated With thrombectomy or reconstruction: however, most patients eventually require retransplantation.
• Stenosis: Affects 5-13% of causes: Dx'd with spectral Doppler with parvus tardus or high peak V>200. MAnage with balloon angioplasty (12).

Common and Proper Hepatic Artery Aneurysm

• The hepatic artery which is common or proper is the second most common type of splanchnic aneurysm accounts for 20%
• The most common site is the common hepatic artery (occurs in up to 63% of cases)
• HAA are related to trauma, atherosclerosis, and fibromuscular dysplasia.
• Can be communicated if with the Portal venous causing arterioportal fistula
• Management: Surgical Ligation of next, embolization, or exclusion

Nonvascular Diseases: Hilar Cholangiocarcinoma

• (Klatskin tumor) originates at the confluence fo right and left and accounts for 50% of bile duct. Mostly over 65.
• Presenting with abdominal issues. Jaundic is LATE
• classified by Bismuth and Corlette

Biliary Strictures

Benign hilar conditions

• Iatrogenic injury related to cholecystectomy or liver transplant Others: primary sclerosing cholangitis and IgG4 Causes: Stone and strictures- manage with endoscopic management

Diseases of the Lymphatics, Nerves, and Connective Tissue

Lymphadenopathy

• The most common cause of the disorders of the hepatic, it occurs. The lymph is 6 mm.
• causes: tumors and metastases - can lead to compression
• Posttransplant can occur frequently extracapsular

Trauma

• Penetrating is frequent
• Mange with vascular and Biliac

PTLD

• Posttransplant a unique complication that character B proliferation. The liver is most common.
• Associated With Epstein- Barr. Extrahepatic is frequent. Can be treated with clinical and serologic.

Periportal Edema

• Can be hepatic venooclusive disease and found with Acute Heptsis