Secondary Metastases to Liver
GI cancers commonly metastasise to the liver, as venous blood returning from the bowel filters through the hepatic portal system first before rejoining the general circulation. Depending on the number and location, it may be possible to resect the affected segment(s) of liver.
Main differentials are simple liver cysts, benign lesions such as haemangioma and liver abscesses. To differentiate between them, the HU value may be helpful. Clinical features (such as fever) are also very useful to know.
Appearance: Irregular heterogenous areas of low attenuation.
Liver Abscess
- Bacterial: Polymicrobial. e.g E. coli, Klebsiella, Streptococci, Enterococci
- Fungal: Candida sp.
- Other: Amoebic (Entamoeba histolytica), Hydatid cysts
Appearance: Bacterial and fungal abscesses usually appear as multiple clustered lesions. Causative features such as biliary obstruction or diverticulitis or appendicitis may also be seen. Amoebic abscess usually appears as a solitary large lesion.
Gallstones
Ultrasound is the gold standard investigation. CT may miss some stones. Plain X-ray only shows 10% of stones. MRCP is useful for ductal stones. Locations: Gallbladder, Bile ducts, Small bowel (rare).
Appearance: On ultrasound, single or multiple hyperechoic objects in the gallbladder, with acoustic shadowing. On CT, stones may be hyperattenuating (calcified stones), isoattenuating (mixed), or hypoattenuating (cholesterol stones) with regards to bile. Isoattenuating stones can be missed. On MRI, stones are an area of low signal (dark).
Cholecystitis
Commonly due to gallstone disease.
Biliary colic: Right upper quadrant pain
Cholecystitis: Right upper quadrant pain + Fever
Ascending cholangitis: Right upper quadrant pain + Fever + Jaundice (Charcot’s triad)
Appearance:
- Distended fluid-filled gallbladder
- Thick enhancing (bright) gallbladder wall
- Fluid surrounding gallbladder
- ‘Fat stranding’ surrounding gallbladder (fluid density due to oedema in fat)
Pancreatic Cancer
Most commonly arises from the head of pancreas. Very poor prognosis due to late diagnosis.
Appearance: Soft tissue mass which may cause obstruction and dilatation of the bile and pancreatic duct systems (“double-duct sign”). Mass may invade into surrounding structures (duodenum, vessels).
Pancreatitis
Release of pancreatic enzymes causes autodigestion of pancreatic tissue, pancreatic ducts, and the surrounding tissues (fat and blood vessels). Complications include peripancreatic fluid collections (if encapsulated, these are called pseudocysts); abscesses; necrosis of pancreatic tissue; thrombosis of splenic/portal veins; and pseudoaneurysms +/- haemorrhage.
Appearance:
- Enlarged, oedematous pancreas
- Fuzzy pancreas borders
- Fluid around pancreas
- ‘Fat stranding’ in retroperitoneum (fluid density due to oedema in fat)
- Areas of non-enhancement indicate necrosis
