Imprisoned

Gastrointestinal System


Diagnosis and reasoning

This patient has presented with jaundice and right upper quadrant pain, a clinical picture suggestive of either hepatic or biliary disease.


Palpation of the abdomen yields a right upper quadrant mass; this concerning finding suggests at either a neoplasm of the liver (such as a hepatic angioma or hepatocellular carcinoma), a liver abscess, or a perhaps, a choledochal cyst.


A liver profile and abdominal ultrasonography are essential next steps. The latter yields a surprise: a multiseptate cystic mass with a wheel-like appearance. This is known as the "snowflake sign", and is essentially pathognomonic of a hydatid cyst (cystic echinococcosis - CE).


The presence of CE is rather unusual here, given the absence of a history of animal contact; however, it is not unprecedented. Note that the aforementioned wheel-like appearance arises from the arrangement of the daughter protoscolices within the cyst.


By standard ultrasonographic criteria, this particular cyst may be classified as an acti

ve stage cyst, most likely CE2.


Serological tests are considered complementary to imaging studies when attempting to confirm the diagnosis of hydatid disease; here, the positive enzyme-linked immunoelectrotransfer blot (EITB) assay confirms the diagnosis, as it is almost 100% specific for CE.


The management of CE depends on the stage of the cyst. In this case, the absence of complications warrants the use of localized puncture, aspiration, injection, and re-aspiration, or PAIR, along with oral Albendazole therapy.


Note that surgical management is the mainstay of treatment in the presence of complications. Radiotherapy has no role in the management of this patient.

Discussion

Hydatid disease is a complex, chronic, and yet often ignored anthropozoonosis, with a global distribution.


The highest prevalence is in low-income regions such as South America, Northern and Eastern Africa, and Eurasia; in high-income nations, the disease may be encountered in recent immigrants.


The condition is caused by the larval or metacestode stage of the tapeworms Echinococcus granulosus and Echinococcus multilocularis; these cause cystic echinococcosis (CE), and the rare variant alveolar echinococcosis (AE), respectively.


Note that CE is the more common form of the disease; AE is far less prevalent, presenting as a ramifying, porous, necrotic mass with an extremely poor prognosis. The remainder of this monograph focuses on CE alone.


The life cycle of E. granulosus commences in the intestine of the definitive host, namely dogs and other canids. Embryonated eggs pass through the feces. Subsequently, herbivores, the intermediate hosts, ingest these eggs, which then hatch into hexacanth larvae in their stomachs.


The larvae penetrate the wall of the small intestine by way of their hooks, enter the portal circulation and travel to the liver and other organs, where they implant and develop into metacestode larvae. These are then ingested by the definitive hosts to complete the life cycle.


Humans occasionally become dead-end hosts from ingesting food contaminated with the eggs. The parasitic life cycle in humans resembles that of the intermediate hosts.


In CE, cysts form in various organs including the liver (75%) and lungs (15%); the clinical findings of the condition are thus due to the mechanical symptoms produced by the enlarging cysts.


The most common presentation is a combination of abdominal discomfort, pain, and a poor appetite. Upon examination, abdominal distension, hepatomegaly, or a palpable abdominal mass are commonly found.


Note that in a significant number of cases, the infection remains silent for years before the cysts enlarge sufficiently to produce symptoms.


The diversity of symptoms mandates that hydatid cysts should always be considered in the list of differentials, when a patient with a likelihood of tapeworm infection presents with jaundice, colicky pain, portal hypertension and ascites, or features suggestive of inferior caval compression.


The diagnosis of CE is usually based on a combination of clinical findings and imaging, with supportive serological tests.


Ultrasonography remains the cornerstone of diagnosis; this also allows the staging of cysts via the International Standardized Ultrasound Classification (WHO-IWGE CE cyst classification), modified from Gharbi et al (1985).


This system classifies CE into either cystic lesions, or active, transitional or inactive cysts, based on their sonographic appearance.


Other imaging modalities of use include Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). They are not, however, as sensitive or specific as ultrasound.


Serological tests are considered complementary to imaging when diagnosing CE. Enzyme-Linked Immunosorbent Assay (ELISA) and indirect hemagglutination (IHA) are usually performed simultaneously, while immunoblotting serves as a confirmatory test.


Note that as many as 20% and 50% of patients with single liver and lung cysts respectively are seronegative at the time of initial diagnosis by ultrasound; this is why serological studies are not employed as a primary diagnostic test.


Inconclusive ultrasound and serologic findings indicate the need for aspiration, with subsequent microscopic analysis for the presence of protoscolices, their components, or antigens specific to E. granulosus.


The treatment of CE has yet to be standardized. There are four principal approaches: watchful waiting, drug treatment for active cysts, percutaneous drainage, and open surgery. The choice of technique depends on the size, stage, and location of the cyst, availability of requisite expertise, and presence of comorbidities.


Watchful waiting is a relatively recent recommendation. It comprises of regularly imaging asymptomatic, uncomplicated, inactive cysts, and is based on the observation that 20% of cysts do transition to the inactive stage and then remain stable over time.


Medical management of CE has been employed since the 1970s, with the use of benzimidazole (BMZ) derivatives. Uninterrupted administration of albendazole (ABZ), which has a superior absorption, for 3-6 months, is the current treatment of choice.


Percutaneous management of abdominal CE aims at either destroying the germinal layer, or complete evacuation of the cyst; currently PAIR (puncture-aspiration-injection-reaspiration) is the most popular technique in this respect, being both diagnostic and therapeutic, with the lowest morbidity and mortality rates of any procedure.


Surgery is the cornerstone of treatment for complicated CE. In expert hands, it can serve to correct cyst rupture, biliary fistulae, hemorrhage, compression of the vital organs, and superinfection. Pre-, peri- and post-operative treatment with a benzimidazole is recommended to minimize seeding and the development secondary CE.

Take home messages

1. Cystic Echinococcosis is a zoonotic disease with a global distribution.

2. In humans, cysts are primarily found in the liver and lungs.

3. Ultrasound is the diagnostic modality of choice, with serology playing a complementary role, especially if imaging findings are inconclusive.

4. PAIR is an effective alternative to medical or surgical management of uncomplicated hepatic CE; it carries the lowest morbidity and mortality rates of any procedure.

References

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