eMedicine Specialties > Gastroenterology > Liver

Hydatid Cysts

Author: Imad S Dandan, MD, Consulting Surgeon, Department of Surgery, Trauma Section, Scripps Memorial Hospital
Coauthor(s): Assaad M Soweid, MD, Assistant Professor, Department of Internal Medicine, American University of Beirut, Lebanon; Firass Abiad, MD, Head of Division, General and Laparoscopic Surgery, Specialized Medical Center Hospital, Saudi Arabia
Contributor Information and Disclosures

Updated: Jun 17, 2008

Introduction

Background

Hydatid disease is a parasitic infestation by a tapeworm of the genus Echinococcus. It is not endemic in the United States, but the change of immigration patterns and the improvement of transcontinental transportation over the past 4 decades have caused a rise in the profile of this previously unusual disease throughout North America. This has led to the necessity for physicians to be more aware of its clinical features, diagnosis, and management.

Pathophysiology

Human echinococcosis is a zoonotic infection caused by the tapeworm of the genus Echinococcus. Of the 4 known species of Echinococcus, 3 are of medical importance in humans. These are Echinococcus granulosus, causing cystic echinococcosis (CE); Echinococcus multilocularis, causing alveolar echinococcosis (AE); and Echinococcus vogeli. E granulosus is the most common of the three. E multilocularis is rare but is the most virulent, and E vogeli is the most rare.

Frequency

United States

Despite the rise in occurrence, echinococcosis remains a very rare disease (<1 case per 1 million inhabitants) in the continental United States. Northern Alaska has endemic areas of E granulosus, but the frequency of infection remains low (<1 case per 100,000 inhabitants).

International

Echinococcosis is also unusual in northern Europe. The endemic areas are the Mediterranean countries, the Middle East, the southern part of South America, Iceland, Australia, New Zealand, and southern parts of Africa; the latter 5 are intensive endemic areas. The incidence of CE in endemic areas ranges from 1-220 cases per 100,000 inhabitants, while the incidence of AE ranges from 0.03-1.2 cases per 100,000 inhabitants, making it a much more rare form of echinococcosis. Infestation with E vogeli is the most rare form of echinococcosis and is reported mainly in the southern parts of South America.

Mortality/Morbidity

• Morbidity is usually secondary to free rupture of the echinococcal cyst (with or without anaphylaxis), infection of the cyst, or dysfunction of affected organs. Examples of dysfunction of affected organs are biliary obstruction, cirrhosis, bronchial obstruction, renal outflow obstruction, increased intracranial pressure secondary to mass, and hydrocephalus secondary to cerebrospinal fluid outflow obstruction.
• In CE, mortality is secondary to anaphylaxis, systemic complications of the cysts (eg, sepsis, cirrhosis, respiratory failure, or operative complications.
• In clinical cases of AE, the mortality rate is 50-60%. This figure reaches 100% for untreated or poorly treated AE. Sudden death has been reported with AE in asymptomatic patients (autopsy diagnosis).

Race

• Because of the restricted geographic distribution of the echinococcal worms, persons of certain races are affected more commonly than others; however, the parasite has the capability of infecting persons of all races equally.

Sex

• No sexual predilection is recognized.

Age

• The cysts grow slowly, and a cyst is rarely diagnosed during childhood or adolescence unless the brain is affected.
• CE is a disease of younger adults, with an average age at diagnosis of 30-40 years.
• AE is a disease of older adults, with an average age at diagnosis of older than 50 years.

Clinical

History

Many hydatid cysts remain asymptomatic, even into advanced age. Parasite load, the site, and the size of the cysts determine the degree of symptoms. A history of living in or visiting an endemic area must be established. Also, exposure to the parasite through the ingestion of foods or water contaminated by the feces of a definitive host must be determined.

• Theoretically, echinococcosis can involve any organ. The liver is the most common organ involved, followed by the lungs. These 2 organs account for 90% of cases of echinococcosis.
• In CE, symptoms can be produced by mass effect or cyst complications.
  • Symptoms due to pressure usually take a long time to manifest, except when they occur in the brain or the eyes.
  • Most symptomatic cysts are larger than 5 cm in diameter.
  • Organs affected by E granulosus are the liver (63%), lungs (25%), muscles (5%), bones (3%), kidneys (2%), brain (1%), and spleen (1%).
• Pressure effects are initially vague. They may include nonspecific pain, cough, low-grade fever, and the sensation of abdominal fullness. As the mass grows, the symptoms become more specific because the mass impinges on or obstructs specific organs.
  • In the liver, the pressure effect of the cyst can produce symptoms of obstructive jaundice and abdominal pain. With biliary rupture, the classic triad of biliary colic, jaundice, and urticaria is observed. Passage of hydatid membranes in the emesis (hydatid emesia) and passage of membranes in the stools (hydatid enterica) may occur rarely.
  • Involvement of the lungs produces chronic cough, dyspnea, pleuritic chest pain, and hemoptysis. Expectoration of cyst membranes and fluid is observed with intrabronchial rupture.
  • Headache, dizziness, and a decreased level of consciousness may signify cerebral involvement. Specific neurologic deficits may occur depending on the location of the cyst in the brain.
• Secondary complications may occur as a result of infection of the cyst or leakage of the cyst.
  • Minor leaks lead to increased pain and a mild allergic reaction characterized by flushing and urticaria. Major rupture leads to a full-blown anaphylactic reaction, which is fatal if not treated promptly. A rupture into the biliary tree can lead to obstruction by the daughter cysts, producing cholangitis. Rupture into the bronchi can lead to expectoration of cyst fluid.
  • Infection of the cyst can occur either as a primary infection or as a secondary infection following an episode of a leak into the biliary tree a cystobiliary fistula. Symptoms range from mild fever to full-blown sepsis.
  • Extremity pain with or without neurologic deficit is a sign of either bone or muscle involvement.
• In AE, the liver is the primary site of infection, and it closely mimics cirrhosis or carcinoma.
  • Symptomatology is that of progressive liver dysfunction that ultimately leads to liver failure.
  • The progression can occur over weeks, months, or years.
  • Distant metastasis is possible, and involvement of other organs (eg, lung, brain, bone) can occur in as many as 13% of the patients.

Physical

Physical examination findings from patients with echinococcosis are nonspecific. The findings are related to the effect of the cyst on the anatomy or the function of the affected organ(s) and to an acute allergic reaction.

• Skin
  • Jaundice could be a sign of biliary obstruction. Spider angiomas are a sign of portal hypertension secondary to either biliary cirrhosis or obstruction of the inferior vena cava.
  • Urticaria and erythema may be seen.
• Vital signs
  • Fever could be a sign of secondary infection or allergic reaction.
  • Hypotension is observed with anaphylaxis secondary to a cyst leak.
• Lungs: Decreased breath sounds over the affected area are signs of airway obstruction with consolidation of the affected segment, lobule, lobe, or the whole lung.
• Abdomen
  • The most common sign is abdominal tenderness. Hepatomegaly may be present or a mass may be felt.
  • Tender hepatomegaly is a sign of secondary infection of the cyst, especially when coupled with fever and chills.
  • Ascites is rare.
  • Splenomegaly can be the result of either splenic echinococcosis or portal hypertension.
• Extremities
  • Bone involvement can result in tenderness over the affected area and, rarely, a palpable mass.
  • Muscle involvement is usually characterized by a palpable mass.
  • Peripheral nerve compression can occur, although extremely rarely. It results in nerve-specific sensory and/or motor deficit.
• Brain
  • Findings from the neurologic examination are nonspecific and depend on the area of the brain involved.
  • They range from very mild to full coma and cerebral herniation.
• Eyes
  • Ocular involvement is rare.
  • Abnormal findings from the ophthalmologic examination include decreased visual acuity, blindness, and exophthalmos.

Causes

Echinococcosis is caused by larval cestodes of the phylum Platyhelminthes (tapeworms).

• Their life cycle involves only 2 hosts, one definitive and the other intermediate. Humans act as an accidental intermediate host. The life cycle has 3 developmental stages, (1) the adult tapeworm in the definitive host, (2) eggs in the environment, and (3) the metacestode in the intermediate host. Metacestodes are ingested by the definitive host. The metacestodes mature into the tapeworm in the definitive host and, in turn, release eggs into the environment. The intermediate host ingests the eggs, which hatch into metacestodes, which infest the liver, lungs, muscles, and other organs of the intermediate host.
• Two biological forms of E granulosus have been recognized (depending on the geographic location and type of intermediate host), (1) the northern type and (2) the European type.
  • The northern type is maintained in the tundra by a predator-prey relationship between the wolf and large deer, but dogs and coyotes can also become infested. Humans become infested in areas where reindeer are domesticated.
  • Intermediate hosts for the European type include camels, pigs, sheep, cattle, goats, horses, and many other animals. The definitive host for the European biotype is overwhelmingly the dog, but it also occurs in foxes, hyenas, and jackals. This is the most common biotype. The adult stage of E multilocularis occurs mainly in foxes and rarely in wolves, coyotes, lynxes, cats, and black bears.
• The intermediate hosts for E multilocularis are 8 families of rodents, including mice, rats, hamsters, gerbils, and squirrels.
• E vogeli is a neotropical species maintained in the bush dog and the paca. It can easily infect other mammals that are exposed to its feces. It is the most rare of the echinococci.
• Exposure to food and water contaminated by the feces of an infected definitive host or poor hygiene in areas of infestation can lead to echinococcosis.

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