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Liver

Anatomy

  • Right Hepatic Vein runs between the right anterior and right posterior segments
  • Left Hepatic Vein runs between the left medial and lateral segments
  • Middle Hepatic Vein runs between the left medial and right anterior segment
  • Echogenic portal triad due to periportal fibrofatty tissue
  • The Ligamentum Teres travels between lateral and medial segments of the left lobe. Contains fibrous umbilical vein
  • Interlobar fissure separates left and right lobe and identifies GB fossa
  • Caudate lobe lies immediately anterior to IVC, separated from the lateral segment of left lobe by the fissure for the ligamentum venosum.
  • Celiac axis → Trifurcation:
    1. Left gastric artery
    2. Splenic artery
    3. Common hepatic artery
      • Gastroduodenal artery to pancreatic head
      • Proper hepatic artery → Cystic, Right, Middle and Left hepatic arteries
  • Replaced right hepatic artery arise from SMA
  • Replaced left hepatic artery arise from the left gastric artery
  • Diaphragmatic fissures: liver indentations at periphery caused by hypertrophied diaphragmatic muscle bundles
  • liver length in midclavicular line 15 cm

Echogenicity in decreasing order

Pancreas, Spleen, Liver, Kidney


Calcified liver masses

Large: Mets, HCC (Fibrolamellar ), old Hematoma, old Abscess
Small: Granulomas, Pneumocystis, Biliary stones, Hepatic arteries


Simple liver cysts

Most common focal liver lesions.

  • Anechoic lumen
  • Increased through transmission
  • Well defined back wall
Many have partial septations.


Complex liver cysts

  • Internal echoes
  • Thick wall
  • Thick Septations
  • Solid elements or Calcifications
DDx: Hematoma, Abscess, Biloma, Echinococcus, Cystic mets, Hemorrhagic or Necrotic Tumors, PCKD: autosomal dominant polycystic disease.


Hemangioma

Most common benign liver neoplasm, 7%, F > M. Typically Homogeneous, Hyperechoic mass < 3 cm, margins are sharp and smooth, may be round or slightly lobulated; Atypical hemangioma has hyperechoic periphery and hypoechoic center - Reverse Target. Flow is too slow to be depicted by Doppler (so if there is a flow it may be mets or HCC). Hemangioma + Thrombocytopenia = Kasabach-Merritt Syndrome


Hyperechoic liver masses

DDx: Hemangioma, Mets, HCC, Focal Fatty Infiltration


Focal Nodular Hyperplasia (FNH)

2nd most common bng liver tu after hemangioma. Central stellate scar not seen on US. 90% females. Usually picked up as hyperenhancing mass during arterial phase of CT. Isodense on nonenhanced CT. Isoechoic or hypoechoic with spoke-wheel pattern of internal vascularity seen on color Doppler.

DDx: · Fibrolamellar HCC (also central scar and spoke wheel), · Hepatic Adenoma, ·HCC, · Hemangioma, · Vascular mets.
Consider hepatic scintigraphy with sulfur colloid

Hepatic Adenoma

Rare bng tu, women taking BCP and men taking anabolic steroids, tends to bleed if > 5 cm, low risk for mlg degeneration. Varied US appearance: uncomplicated - homogeneous and hypoechoic. Internal hemorrhage or necrosis --> heterogeneous and/or complex cystic components. Intratu fat --> hyperechoic, calcifications in 10%


Metastasis

Most common mlg tu of the liver.
Target lesion: Echogenic or Isoechoic center and a hypoechoic halo (also HCC)
Hyperechoic mets: GI tract and neuroendocrine tu
Calcified mets: Colon, Mucinous primary tu of ovary, Breast and Stomach.
Breast ca: diffusely heterogeneous widespread mets through the liver
DDx: Cirrhosis, Hepatic fibrosis, Hepatic Lymphoma, Fatty infiltration, Diffuse HCC


HepatoCellular Carcinoma (HCC)

Solid mass in patient w/ cirrhosis or chronic hepatitis.
Propensity to invade portal vein (50%) → detection of intravenous soft tissue in a patient w/ hepatic mass = HCC.
RF: Aflatoxin in Asia, ETOH, hemochromatosis, Wilson’s disease elsewhere.
Development: Regenerative nodule → Adenomatous hyperplasia → HCC.
HCC: Solitary, Multifocal, Diffuse, Infiltrating. Satellite lesions. Echogenicity varies. Hypervascular (Doppler signal). FHCC: Fibrolamellar HCC contains calcs.


Lymphoma

Hypoechoic mass simulates Mets, Target lesion, non-Hodgkin, AIDS, post-transplantation. Almost never hyperechoic or cystic with calcs


Pyogenic liver abscess

Seeding from Appendicitis, Diverticulitis, Cholecystitis, Cholangitis, Endocarditis. Complex fluid collections w/ mixed echogenicity w/ through transmission (liquid). DDx: Hematoma, Hemorrhagic cyst, Necrotic or Hemorrhagic tu


Fungal liver abscess

Candida microabscesses, Target lesions (central echogenic region w/ hypoechoic halo, like mets), early lesions may have a hypoechoic focus centrally (wheel within a wheel); with healing become hyperechoic and calcify


Pneumocystis carinii

Multiple, small, non-shadowing echogenic foci scattered throughout the liver.


Echinococcus

Forms endocyst (inner membrane), ectocyst (outer membrane) and host forms pericyst around it. Relatively simple cyst w/ multiple daughter cysts, cyst w/ detached floating endocystic membranes, cysts w/ internal debris and calcs


Hepatitis

Starry sky: increased echogenicity of the portal triads


Fatty liver

Uniform echogenicity distinctly greater than that of the renal cortex, loss of portal triads visualization in the periphery of the liver. Poor sound penetration w/ loss of definition of the diaphragm. Focal sparing around portal vein bifurcation and GB. Focal fatty infiltration: left lobe adjacent to the falciform ligament and anterior to the portal vein bifurcation.


Cirrhosis

Coarsened and inhomogeneous parenchyma, nodular surface, ascites


Portal Hypertension

Normally minimal or no pulsatility in portal vein (prominent w/ CHF). Normal velocity 20-30 cm/sec, normal hepatopedal flow; away from the liver is hepatofugal - hepatic veins. Hepatic vein triphasic waveform: after atrial contraction → rapid filling of atrium - S phase; tricuspid valve open - D phase; atrium contracts again - A phase (blunted in hepatic vein thrombosis (Budd-Chiari), cirrhosis, diffuse mets)

Portal HTN:

  • Intrahepatic
    • Postsinusoidal: Cirrhosis, Veno-Occlusive disease
    • Presinusoidal: Lymphoma, Hepatic fibrosis, Schistosomiasis, Sarcoidosis
  • Extrahepatic
    • Prehepatic: portal vein thrombosis (intraluminal filling defects), PV compression
    • Posthepatic: Hepatic vein thrombosis [Budd-Chiari] (collaterals through caudate lobe, supplying hepatic vein will have reversed flow), IVC obstruction, constrictive pericarditis
    • Hyperdynamic: arterio-portal fistula

Sonographic signs of Portal hypertension

Splenomegaly, Ascites, Portosystemic collaterals, reversal of portal vein flow, enlarged hepatic veins, Umbilical and Coronary veins recanalization

Portal vein thrombosis → collaterals in the hepatoduodenal ligament and the wall of the common bile duct ⇒ cavernous transformation of the portal vein

Hepatic congestion

Heart failure, Hepatomegaly, Enlarged hepatic veins, Enlarged IVC; Prominent pulsatility of portal vein (below Doppler baseline)


Transjugular Intrahepatic Portosystemic Shunt (TIPS)

US role is to evaluate shunt patency
Indications: Bleeding esophageal varices, Intractable ascites
Flow in the right and left portal vein reverses into stent (hepatofugal flow instead of hepatopedal). Normal flow velocities in the stent 90-190cm/sec. Signs of stenosis is increased velocity in the stent, decreased portal vein flow and reversal of flow in hepatic veins draining the stent.

MELD (Model for End-Stage Liver Disease): Assess severity of chronic liver disease; TIPS scores > 24: increased mortality; Child-Pugh scores: old system; pressure gradient to achieve when placing TIPS is 12 mm Hg;

Complications of TIPS: Hepatic encephalopathy w/ low pressure gradients (majority of blood flows through the TIPS and bypassing liver), exacerbation of CHF (increased porto-systemic shunt)