Hepatic Cysts

Simple Hepatic Cysts

Simple hepatic cysts are presumed to originate from the biliary tree, likely from microhamartomas or peribiliary glands that become isolated from the bile ducts. They are lined with a simple cuboidal epithelium and surrounded by a fibrous, hypocellular stroma. Cyst contents are typically serous, but proteinaceous material from previous hemorrhage may be present. The presence of mucinous or solid contents should prompt consideration of an infectious or neoplastic process.

Hepatic cysts have long been recognized as an incidental finding at laparotomy, during autopsy, or on imaging studies. Estimates of the prevalence of liver cysts range from 11% to 18%, depending on the imaging modality used. Hepatic cysts become more common with increasing patient age; more than 92% of cysts occur in those older than 40 years. Some studies have shown a higher incidence of cysts in female patients.

Although the majority of simple hepatic cysts are asymptomatic and discovered incidentally, some patients will experience abdominal pain or distention. Symptoms may be related to stretch of the liver capsule causing pain or mass effect on surrounding structures. Symptoms are more common in older patients with larger cysts. Progressive cyst enlargement may lead to early satiety, nausea, and vomiting. A palpable mass on physical examination may be infrequently noted.

Simple cysts do not generally result in abnormalities of liver function tests. Echinococcal serology should be obtained if there is appropriate clinical suspicion or characteristic imaging findings. Liver abscesses are usually accompanied by other signs of infection. For most patients, the main challenge is to differentiate neoplastic from nonneoplastic cysts, which depends on imaging.

Hepatic ultrasound is the preferred initial study because it is inexpensive, noninvasive, and highly informative. It reliably distinguishes between cystic and solid hepatic lesions and can suggest the diagnosis of a cystic neoplasm. Simple hepatic cysts appear sonographically as anechoic masses with smooth margins and imperceptibly thin walls ( Fig. 121.1 ). The differential reflection of ultrasound waves by the cyst wall and cyst fluid leads to back-wall enhancement. Septations or nodularity should prompt suspicion of a neoplastic cyst. Lack of septations is highly predictive of a simple hepatic cyst. However, it is important to remember that simple cysts are common, whereas neoplastic cysts are rare. Therefore, even if septations or other complex features are found in a liver cyst, it is still more likely than not to be nonneoplastic.

Cross-sectional imaging with either computed tomography (CT) or magnetic resonance imaging (MRI) can be very useful in further characterizing a cyst and assessing its anatomic relationships. CT scans should be performed with intravenous contrast timed to delineate arterial, portal venous, and hepatic venous structures. On CT, simple cysts should appear as nonenhancing lesions of water density (0 to 10 Hounsfield units) with smooth, imperceptible walls ( Figs. 121.2 and 121.3 ). Wall thickening or irregularity, papillary mural projections or nodules, internal septations, and intracystic debris should prompt consideration of a neoplastic etiology. CT scans are widely available and well tolerated by patients, but they may fail to adequately characterize smaller lesions. MRI is particularly useful for evaluating smaller lesions and is our imaging modality of choice for patients with newly discovered liver lesions.

On MRI, simple hepatic cysts have homogeneous, very low signal intensity relative to surrounding liver parenchyma on T1-weighted images but very high signal intensity on T2-weighted images. They do not enhance with administration of gadolinium chelates ( Fig. 121.4 ). Cysts with internal hemorrhage will appear hyperintense on both T1- and T2-weighted images and often demonstrate a fluid-fluid level ( Fig. 121.5 ). MRI provides detailed information about internal cystic structure, including septations, papillary nodules, and debris. In addition, small lesions that are indeterminate on CT scan can often be accurately characterized by MRI ( Fig. 121.6 ). Diffusion-weighted MRI is particularly useful in distinguishing small hepatic cysts from other benign and malignant liver lesions.

Intervention is indicated in patients with symptoms attributable to a hepatic cyst or uncertainty regarding a neoplastic etiology. Image-guided aspiration is ineffective, with a recurrence rate of 100%. However, aspiration can provide fluid for biochemical and cytologic analyses. Aspiration may also help to assess whether symptoms are related to the cyst because it should provide temporary improvement of symptoms.

Aspiration with the addition of a sclerosant, such as ethanol, hypertonic saline, or tetracycline, has resulted in improved recurrence rates. Communication with the biliary tree must be ruled out before a sclerosant is used. In one prospective study of percutaneous aspiration and ethanol injection, 80% of patients demonstrated recurrent cysts; however, the majority of these regressed and did not require retreatment. Other small series have reported recurrence in as few as 17% of patients. The majority of cysts treated with percutaneous aspiration and sclerosant injection decrease in size, with a mean volume reduction of 92% to 98% at a 30-month follow-up.

Surgical cyst fenestration or resection remains the mainstay of treatment for symptomatic simple hepatic cysts. Cysts that are deep in the parenchyma may not be suitable for fenestration, but only a portion of the wall needs to be removed to achieve symptomatic relief and rule out neoplasm. Therefore cyst fenestration is a reasonable first step in any medically fit patient with even a portion of the cyst that is superficial and accessible. Cyst fenestration or resection may be carried out via a laparoscopic or an open approach.

Regardless of the surgical treatment selected, the operation begins with visual inspection. Intraoperative ultrasound can identify and define the cyst's relationship to the biliary tree and vasculature. The cyst should then be aspirated, with fluid sent for cytology. A large portion of the cyst wall (as much as can be removed without a liver resection) should be resected. Nodules or papillary projections in the remaining cyst wall may be separately biopsied. Bilious cyst fluid should prompt careful examination for a connection to the biliary tree, and bile leaks should be oversewn. If there is sufficient preoperative concern for a neoplastic process, a formal resection or enucleation may be carried out rather than fenestration.

For patients who undergo cyst fenestration, whether laparoscopic or open, recurrence rates are less than 10%. Morbidity is also less than 10%. For patients treated with hepatic resection, recurrence is extremely rare, but morbidity and mortality rates exceed those associated with fenestration. A prospective nonrandomized study of 40 patients with simple hepatic cysts demonstrated increased length of stay, operative blood loss, and complication rates in patients treated with resection compared with open fenestration. Laparoscopic fenestration carried the lowest morbidity, with no significant difference in recurrence rates among the different surgical procedures. Therefore laparoscopic fenestration should be considered the procedure of choice for symptomatic simple hepatic cysts with low suspicion for neoplasm.