Picture Quiz: Circular shadows in the lung field

A 43 year old farmer, a chronic smoker and an alcoholic, was admitted with blood tinged sputum, dry hacking cough, heaviness in the chest, and breathlessness for more than three years. He had no history of fever, night sweats, weight loss, or anorexia. Upon examination he had 5 cm, non-tender, smooth surfaced, enlarged liver and dullness in the right and left apical and mid-zone of both lungs. The base of the right side was also dull on percussion with bronchial breathing. After admission, all investigations, including haemogram, blood sugar, serum electrolytes, and liver and kidney functions were normal.

Questions

(1) Describe the findings in the chest radiograph (Fig 1)?

(2) What are the differential diagnoses of the chest radiograph?

(3) What is the most likely clinical diagnosis?

(4) What other confirmatory tests may be indicated?

(5) How should you manage this case?

Answers

(1) The chest radiograph (posteroanterior view) shows multiple oval to circular shadows, small to large in size, distributed in both lung fields. The shadows are well demarcated and homogenous. There is no evidence of calcification or rib erosion. The mediastinum looks central and normal.

(2) Hydatid disease of the lung, intralobar pulmonary sequestration, aspergillosis, cavitating bronchiogenic carcinoma, Wegener's granulomatosis, and bronchogenic cysts.

(3) Hydatid disease of the lung.

(4) Computed tomography of the thorax, serological tests-indirect haemagglutination tests, and immunofluorescent tests.

(5) Medical management-albendazole and praziquantel. Surgical management-removal or percutaneous aspiration injection reaspiration in selected cases.

Fig 1 The chest radiograph

Discussion

Hydatid disease or echinococcosis is the general term for four diseases that are caused by the larval stage of the echinococcus tapeworm, the smallest in the Taeniidae family. It remains one of the most intractable and lethal helminthic diseases. Its distribution is not only confined to the tropics or to developing countries but also to rich countries. Echinococcus granulosus causes cystic echinococcosis and is prevalent in South America, around the Mediterranean coast, the Middle East, central Asia, and East Africa. Small focuses of infection are still found in north Wales and rural Scotland. E multilocularis causes alveolar echinococcosis and is found in only the Northern hemisphere. E vogeli and E oligarthrus rarely cause human disease.

E granulosus is the most common of the four species and has a definite host, usually a dog, and intermediate hosts, such as sheep, goats, and pigs (fig 2). Humans are incidental hosts and typically are not involved in the life cycle. Humans usually become infected through exposure to canine faeces. The pastoral strain of E granulosus is more pathogenic to humans and has a transmission cycle in which dogs are the definitive host and sheep, cattle, and other domestic livestocks are intermediate hosts. Cysts of the sylvatic or northern strain tend to form in the lungs.

E multilocularis is the second most common species. The fox is its definitive host, and microtine rodents are its intermediate host. The primary localisation of alveolar cysts is in the liver, where they may extend locally or metastasise to other organs. The larval mass has poorly defined borders and behaves like a neoplasm: it infiltrates and proliferates indefinitely by exogenous budding of the germinative membrane (brood capsule), producing an alveolus-like pattern of microvesicles. Pulmonary involvement is rare.

Sites of involvement in descending order of commonness are liver, lung, spleen, skin, muscle, kidney, retroperitoneum, bone, heart, and brain.

Anatomy of cysts

The cyst wall has three layers-a delicate inner translucent membrane, which gives rise within the cyst to germinal elements; a supporting intermediate layer, which has a consistency of cooked egg white; and an outer layer produced by the host, which often calcifies.

Dissemination of germinal elements may be followed by the development of multiple secondary cysts. Cysts in the bone marrow or spongiosa do not have a host layer and are irregular in shape, erode osseous tissue, and present as pain or spontaneous fracture.

Diagnosis: history

Patients present with a wide range of symptoms, from none to sudden death from anaphylactic shock after spontaneous rupture of the cyst or cardiac involvement. Generally these cysts are discovered through routine imaging.

Symptoms are caused by pressure effects; pulmonary cysts present as chronic cough, haemoptysis, and breathlessness. Because lung tissue hardly compresses surrounding tissue, cysts develop a thin pericyst capsule, which can rapidly become larger and is more prone to spontaneous rupture.

Liver cysts present as pain in the right upper quadrant and as nausea and vomiting. The effect of pressure may result in biliary obstruction, with secondary biliary cholangitis, cirrhosis, and portal hypertension. A clinical syndrome characterised by jaundice, biliary colic, and urticaria may follow intrabiliary extrusion of cyst content. Cysts in the brain produce symptoms earlier and may cause seizures or symptoms of increased intracranial pressure. They should be considered as a cause of stroke in young patients.

Fig 2 Life cycle of the echinococcus tapeworm

Bone cysts present as pain and spontaneous fracture. Vertebrae are most commonly affected. And cardiac cysts present as tumour, pericardial effusion up to tamponade, complete heart block, and sudden death.

Some patients present with non-specific complaints of loss of appetite, weight loss, and weakness. A fifth have multiple cysts at diagnosis, so each patient should be screened for cysts at other sites.

Diagnosis: investigations

Imaging studies are generally the first line of investigation. If confusion arises, serological tests can confirm the disease. Chest radiography may show floating membranes (water lily sign), and computed tomography may show separation of membranes from the wall. Ultrasonography is used for abdominal cysts.

Common serological assays to confirm hydatid disease are enzyme immunoassay (identify antigen B), western blot assay (identify specific antigens of 8, 16, and 21 kDa), indirect haemagglutination, and indirect fluorescent antibody. Serious drawbacks in serological diagnosis are its low sensitivity for detection of hydatid cysts and cross reactivity with serums of patients with Taenia solium infection.

Eosinophilia is uncommon except after cyst rupture. The intracutaneous skin test (Casoni's test) is no longer used because of poor specificity.

Surgical management

Surgical removal of cysts is the treatment of choice. Hepatic cysts are generally treated by partial hepatic resection, pericystectomy, or cystectomy. The residual cyst cavity may be reduced by packing the space with pedicled greater omentum (omentoplasty). Pulmonary cysts are treated by Barret's procedure (extrusion of cysts), pericystectomy, and lobectomy. Before removal, scolicidal agents are put into the cyst cavity. Commonly used scolicidal solutions are 20% hypertonic saline, 70-95% ethanol, 5% cetrimide, and 3.75% sodium hypochlorite. These agents are not used when liver cysts are thought to communicate with the biliary tract.

Percutaneous aspiration injection reaspiration is becoming the treatment of choice if there are no contraindications. The procedure involves percutaneous puncture using sonographic guidance, aspiration of substantial amounts of cyst fluid, and injection of a scolicidal agent for at least 15 minutes followed by reaspiration of cystic contents.

Albendazole may be given for 1-4 weeks before surgery and for 2-4 weeks after. Praziquantel is given as adjunct treatment in two doses (one before and one after the operation) of 5-10 mg/kg for both children and adults.

Medical management

A total of 15 mg/kg/day of albendazole is given in two divided doses with meals for 3-6 months. In some cases treatment may continue for up to five years. Praziquantel is used as adjunct treatment because it only kills the inside of the hydatid cyst and not the germinal layer. It should not be used for E multilocularis infection because the drug may aid alveolar hydatid growth.

Prevention

Education and public health measures are the most effective tools for control of hydatid disease.

Pratyush Ranjan, MBBS intern, affiliation
Email: drpratyushranjan@yahoo.co.in
R N Das, consultant in infectious disease, Manipal College of Medical Sciences, Pokhara, Nepal



studentBMJ 2006;14:441-484 December ISSN 0966-6494