Monday, June 11, 2012

Focal Liver Mass: Differential Diagnosis #24

A focal liver mass can represent a wide spectrum of pathology, from benign to highly malignant. Being able to distinguish between various diagnoses is critical for establishing an appropriate treatment plan. Unfortunately, there is no ideal modality for doing this - while one can use ultrasound, CT, MR, and nuclear medicine, each has its own limitations. However, knowing some basic features can help narrow the diagnosis.

This post will focus on the appearance of solid hepatic lesions (as opposed to cystic lesions),  as well as their appearance on CT. There's no good mnemonic for this, but try and stay CALM my Fine Happy Friend, if you see such a lesion:

CCavernous hemangiomaMost common benign mass, second most common mass after mets; enhance peripherally first, delayed washout
AAdenomaTypically solitary; seen in women on OCP, men on steroids, or glycogen storage disorders; increased bleeding risk -> surgical removal
LLymphomaMultiple low density nodules; resemble microabscesses in Hodgkin's lymphoma; associated with splenic involvement
MMetastasesMost common malignancy (18:1 vs primary HCC)
hypovascular: colon ca
hypervascular: RCC, thyroid, melanoma, choriocarcinoma
calcified: mucinous adenocarcinoma, osteosarcoma, chondrosarcoma
cystic: mucinous colon ca, lung, carcinoid, melanoma

FFibrolamellar carcinomaLarge mass in a young, healthy person; slow growing; central scar, which may calcify (50%)
HHepatocellular carcinomaArterial hypervascularity; 25% calcify; portal/hepatic vein invasion common
FFocal nodular hyperplasiaCentral scar; contain all normal liver elements; take up sulfur colloid on nuclear scans

Hepatic Adenoma (Portal Venous Phase)
Source: Radiopaedia
To evaluate this lesions, a radiologist may perform a "multi-phase" or "four phase" CT. The phases are as follows:

  1. Non-contrast: prior to contrast injection
  2. Arterial phase: 30 seconds after contrast injection
  3. Portal venous phase:  70 - 90 seconds after injection. 
  4. Delayed phase: 5 - 10 minutes after contrast injection

The texts below have more detailed descriptions of how each lesions appears during each phase.