Simple cystic lesion:
Simple cystic lesions mostly demonstrate a thin,
regular wall,
smoothly demarcated (Fig 1).
This features is often seen like in simple biliary cysts (Fig 2).
The content is homogeneous with water like density at CT and high signal intensity on MRI at T2-weighted images (Fig 3).
Sometimes a thin peripheral located septum can be observed in simple biliary cysts (Fig 4 and 5).
No treatment is required for this type of lesions.
Sometimes alcohol sclerosis or fenestration is performed because of mechanical complaints.
Cystic lesion with internal septations:
Internal septations are present in complex cystic lesions (Fig 6).
Mostly these lesions demonstrate a thin,
smooth wall.
This can be due to complication in a simple biliary cyst,
such as bleeding or infection.
These lesions must be differentiated from biliary cystadenoma,
which is a premalignant lesion that requires surgical removal.
Typically in biliary cystadenoma,
multiple internal septations are demonstrated with CT or MRI (Fig 7),
with enhancement of the septations after administration of contrast material (Fig 8).
Because of the enhancement of the internal structures,
differentiation between a complicated benign lesion and neoplastic lesion,
biliary cystadenoma (or multilocular cystic neoplasm),
can be assessed.
Thess lesions almost exclusively presents in middle-aged women.
Cystic lesion with internal septations and solid nodules:
Solely based on imaging findings,
biliary cystadenocarcinoma is sometimes difficult to differentiate from biliary cystadenoma.
When mural enhancing nodules are demonstrated in the cystic lesion with internal septations (Fig 9),
this finding favors the diagnosis of biliary cystadenocarcinoma (Fig 10).
This type of tumor affects elderly patients,
both men and women.
Therapy is surgery for this type of cystic lesions.
Cystic lesion with thick irregular wall with solid components:
An irregular,
thick wall with enhancement and solid nodular enhancing components are often seen in malignant,
neoplastic lesions (Fig 11).
Some highly aggressive tumors with frank necrosis demonstrate this growth pattern,
like embryonal sarcomas.
Altough infrequent,
HCC or cholangiocarcinoma (Fig 12) can present as a predominantly cystic lesion.
Cystic lesions with multiple internal cysts:
Echinococcus granulosis or multilocularis are worm infections,
which can cause hydatide or echinococcal cysts in many organs.
Typical aspect in the liver is a large cystic lesion with smaller daughter cysts (Fig 13).
Wall calcifications are frequently present (Fig 14).
It is important to differentiate this lesion from other cystic lesions,
because the first choice of therapy is medical treatment.
Cystic lesion with thick irregular wall and surrounding hypodens liver parenchyma:
Infectious lesions can coalesce and form an pyogenic abscess,
with a thick irregular rim en hypodens centre due to necrosis (Fig 15).
The surrounding liver parenchyma can be slighty hypodens to the normal liver parenchyma (Fig 16).
Clinical symptoms are often a clue to the diagnosis.
Aspiration and drainage is the preferred therapy.
Pitfall:
When evaluating cystic liver lesions,
it is sometimes difficult to evaluate the content of the lesion using CT (Fig 17).
Internal septations and soft tissue components are more easily observed with MRI or US,
especially when only a portalvenous phase CT is available.
Looking carefully at the borders of a cystic lesion is mandatory.
If any doubt,
an additional MRI or US (Fig 18) can be performed to differentiate simple and complex cystic lesions.