Imaging of Liver

Liver Imaging Toolkit - Modality Mania

• USG (Ultrasound): Initial, non-invasive. Assesses size, echotexture, focal lesions (cysts, solid), steatosis. Doppler for vascularity.
• CT (Computed Tomography): Workhorse. Non-contrast (fat, $Ca^{2+}$, blood).

  ⭐ Typical Liver Triphasic CT Enhancement:

  • Arterial Phase (~25-35s): Hypervascular lesions (HCC, FNH, adenoma, hemangioma [peripheral]).
  • Portal Venous Phase (~60-80s): Peak parenchymal enhancement; most metastases.
  • Delayed Phase (~3-5+ min): Washout (HCC); delayed enhancement (cholangiocarcinoma, hemangioma [centripetal fill-in]).

• MRI (Magnetic Resonance Imaging): Superior soft-tissue contrast. Problem-solving. Sequences: T1, T2, DWI, hepatobiliary agents.
• Elastography: Assesses liver stiffness (fibrosis).

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Benign Bumps - Friendly Formations

• Hemangioma: Most common benign lesion.

  • US: Hyperechoic. CT/MRI: Peripheral, discontinuous, nodular enhancement; centripetal fill-in.

  ⭐ Hemangiomas typically show peripheral, discontinuous, nodular enhancement that fills in centripetally on dynamic contrast-enhanced CT/MRI.

• Focal Nodular Hyperplasia (FNH):

  • Arterial: Intense, homogeneous enhancement (scar may not).
  • Central scar: T2 bright, delayed enhancement.
  • Gadoxetate: Uptake (vs. adenoma).

• Hepatic Adenoma:

  • OCP/steroid link. Risk: Hemorrhage, malignant change (rare).
  • Heterogeneous (fat/bleed). Arterial enhancement.
  • Gadoxetate: Usually no uptake.

• Simple Cyst:

  • US: Anechoic. CT: 0-20 HU (water). T2: Markedly bright. No enhancement.

Malignant Masses - Nasty Newcomers

• Hepatocellular Carcinoma (HCC): Most common primary. Risks: Cirrhosis, HBV, HCV.

  ⭐ HCC: Classic arterial phase hyperenhancement (APHE) & portal/delayed washout (LI-RADS major feature).

  • Other features: Capsule, mosaic pattern.
• Cholangiocarcinoma (CCC): Intrahepatic or perihilar. Features: Delayed enhancement, capsular retraction, biliary dilatation.
• Metastases: Most common liver malignancy overall. Appearance varies.
  • Hypovascular: e.g., Colorectal.
  • Hypervascular: e.g., NET, RCC, Melanoma. 📌 Mnemonic (Hypervascular): Melanoma, RCC, NET, Thyroid (MR. NT).
• LI-RADS: Standardizes HCC risk reporting (e.g., LR-5 for definite HCC).

Sick Spreads - Diffuse Dilemmas

• Cirrhosis:

  ⭐ Imaging: Nodular surface, caudate hypertrophy, portal hypertension (splenomegaly, varices, ascites).

  • Fibrosis, regenerative nodules. Complications: HCC.
• Hepatic Steatosis (Fatty Liver):
  • US: ↑ Echogenicity (bright liver).
  • CT: ↓ Attenuation (< 40 HU, or < spleen by 10 HU).
  • MRI: Signal loss on out-of-phase imaging.
• Hemochromatosis (Iron Overload):
  • CT: ↑ Liver density.
  • MRI: ↓ T2/T2* signal intensity (paramagnetic effect).
• Wilson's Disease (Copper):
  • Variable: cirrhosis, steatosis, acute hepatitis.

Vascular & Trauma - Flow & Fracture

• Budd-Chiari Syndrome (BCS): Hepatic vein obstruction. CT/MRI: hepatomegaly, ascites, caudate hypertrophy, patchy enhancement ("nutmeg liver").

  ⭐ Budd-Chiari syndrome imaging often reveals hepatomegaly, ascites, and characteristic 'nutmeg liver' or 'flip-flop' enhancement pattern of the caudate lobe due to its separate venous drainage.

• Portal Vein Thrombosis (PVT): Portal vein clot. US/CT: filling defect, cavernous transformation (chronic).
• Liver Trauma (CT is key):
  • Lacerations: Graded (AAST).
  • Hematomas: Subcapsular, intraparenchymal.
  • Active bleed: Contrast extravasation. oka

High‑Yield Points - ⚡ Biggest Takeaways

• HCC: Key features are arterial phase hyperenhancement and subsequent portal venous/delayed phase washout.
• Liver Metastases: Most common malignant liver tumor; imaging appearance is highly variable.
• Hemangioma: Most common benign liver tumor; shows peripheral nodular enhancement with centripetal fill-in.
• FNH: Often presents with a central scar; demonstrates intense, homogeneous arterial enhancement.
• Cirrhosis: Imaging signs include nodular liver surface, caudate lobe hypertrophy, and portal hypertension.
• Hydatid Cyst: Characterized by pathognomonic daughter cysts or the "water lily sign".