Figure 5.1 Life cycle of E. granulosus. (Reproduced with permission from DPDx, Centers for Disease Control, http://www.cdc.gov/dpdx/echinococcosis/.)

5.9.2  Nature of the cyst (structure and terminology)

A good knowledge of the macroscopic and microscopic structure of the echinococcal cyst is crucial to its successful treatment. Figure 5.2, reproduced from the WHO Informal Working Group on Echinococcosis (IWGE) consensus [32] outlines the structure. Importantly, the adventitial layer or pericystic tissue is considered part of the cyst, and information on whether it is removed helps define the operation performed (see below). The key to cyst growth and development is the germinal membrane, a syncytial layer one cell thick, which lays down the acellular laminated membrane on its outer surface and produces the internal contents of the cyst, namely, cyst fluid, brood capsules, themselves containing protoscoleces, and daughter cysts. Histological appearances are shown in Figure 5.3. CE grow at between 1 and 50 mm per year, but may also remain static for months to years. Cyst size at clinical presentation can be as large as 20 cm, but is more commonly 5–10 cm [33]. Unlike the situation in adults, liver cysts occur less commonly than lung cysts in children. Furthermore, combined liver and lung cysts occur more frequently in children than in adults [34]. In the liver, cysts occur most commonly in segments VII and VIII. Segment IV cysts carry the highest risk of involving the biliary tract [35].

5.9.3  Clinical presentation

Clinical presentation of hepatic CE includes an incidental diagnosis of asymptomatic cysts, abdominal swelling, right upper quadrant pain, jaundice or anaphylaxis due to rupture into the biliary tree [35], acute onset of pain secondary to rupture through the liver capsule into the peritoneal cavity and pleural effusion secondary to rupture through the diaphragm.

Complications might include ascites secondary to peritoneal dissemination, secondary bacterial infection and chemical cholangitis secondary to intrabiliary rupture [36].

There are no pathognomonic features on history or examination. Thus, CE must be included in the differential diagnosis of all these presentations from the outset, especially in children from high-prevalence areas.

Figure 5.2 Diagrammatic representation of structure of the echinococcal cyst. (Reproduced with permission from Brunetti E, et al., Acta Tropica 2010, 114: 1–16.)

Figure 5.3 Exploded view of histology of CE. (a) Protoscolex, (b) germinal membrane, (c) laminated membrane. (Reproduced with permission from P.L. Chiodini.)

5.9.4  Imaging

CE does not take a single form. Cysts vary in type, and an individual liver may contain one, a few or several cysts, which may themselves be of different ages, at different stages of development, viable, transitional or nonviable. This makes comparative evaluation of treatment series difficult.

A standardised classification of cyst type which reflects the natural history of parasite development from undifferentiated simple cyst through to an inactive degenerate stage must therefore be used in clinical care. The WHO-IWGE US classification of cyst types [37] is shown in Table 5.1. For consistency, it should be used in place of the older Gharbi^* classification [38]. Strictly, these US-based classifications do not apply to cross-sectional imaging modalities, although MR seems to correlate more closely than CT. MR scan, however, does not show calcification. Investigation of childhood hepatic CE should also include imaging of the lungs to exclude or confirm involvement of both organs.

5.9.5  Type of cyst and natural history

The natural history of untreated CE and the resulting sequence of hydatid cyst structure is only partially known, but some patterns are seen regularly; for example, CE1 becomes CE3a, CE1 becomes CE2 and CE3a becomes CE2. The crucial watershed lies between the active and transitional types and the inactive types. CE4 and CE5 are inactive. They can simply be followed up and there is no need to treat them unless they develop significant complications, for example, secondary bacterial infection and abscess formation.

Table 5.1 WHO-IWGE vs. Gharbi classification of CE of the liver

(b) Reproduced with permission from Brunetti E, et al., Acta Tropica 2010, 114: 1–16.

5.9.6  Serology

There is no single standardised test for the detection of antibodies to CE. The most common tests are ELISA, indirect haemagglutination and latex agglutination, with Western blotting used for confirmation [39]. Sensitivity for hepatic CE is 85%–98% [32], but up to 20% of patients with single liver cysts may be seronegative at diagnosis, with CE1 and CE4 or CE5 cysts being most likely to be seronegative. Those with multiple hepatic cysts are usually seropositive [40].

Serology is an adjunct to imaging-based diagnosis of CE but not an absolute arbiter, and clinicians need to be aware of important serological cross-reactions which can result in false positives. The most common ones are E. multilocularis (alveolar echinococcosis ([AE]), Taenia solium cysticercosis, schistosomiasis, liver flukes, filariasis, malignancies (especially of the gastrointestinal tract) and cirrhosis [39,40]. Differentiation of CE from malignancy is clearly a critical diagnosis, emphasising the need for cases of suspected CE to be evaluated by those experienced in its presentation, imaging characteristics and specific diagnostics.

5.9.7  Treatment

The WHO-IWGE expert consensus group have produced clinical guidelines for treatment, but in the absence of randomised trials, they remain simply recommendations. Nabarro et al. [41] conducted an international survey of the management of CE in which hydatid clinicians were asked how to manage five actual clinical cases. Most did not follow the WHO-IWGE consensus, and there was great variation in reported practice, with treatments known to be ineffectual, outdated or unsafe being suggested.

5.9.7.1  SURGERY

The indications for CE liver surgery [32,40] are

• Removal of large CE2 or CE3b cysts with multiple daughter vesicles not suitable for percutaneous treatment (PT)

• Single liver cysts, situated superficially, that may rupture spontaneously or as a result of trauma when PTs are not available

Table 5.2 Paediatric surgical series in CE

• Infected cysts when PTs are not available

• Cyst rupture

• Cysts communicating with the biliary tree as an alternative to PT

• Cysts exerting pressure on adjacent vital organs

• Haemorrhage

The aim is to inactivate the parasite (cyst content); remove as much parasitic material as possible, minimising leakage or spillage of cyst contents, which might result in secondary dissemination or local recurrence; and then manage the residual cavity. It should be noted that protoscoleces and fragments of the cyst wall (if the germinal membrane is viable) are both capable of developing into cysts if left behind at operation.

A variety of terms for CE operations are to be found in the literature, making precise comparison between published studies difficult. Pawlowski [42] clarified terminology for cyst structure and related it to operation type:

• Hepatic resection: Removes the entire cyst, including the pericyst, intact

• Pericystectomy: Removes the endocyst (defined as the laminated membrane plus germinal membrane and cyst contents) along with the surrounding compressed liver tissue (pericyst)

• Cystectomy: Removes just the endocyst

Other techniques have been reported particularly to resolve or obliterate the cavity created and include capitonnage,^* filling it with omentum (omentoplasty), external tube drainage and marsupialisation.

Ultimately, the choice of operation depends on the characteristics of the cyst, its site and the experience of the surgeon, but where possible, CE should be managed in centres expert in its care.

Most of the literature on surgery, and indeed for percutaneous techniques for CE, relates to cases in adults, and reported paediatric experience only is limited. Table 5.2 illustrates specific paediatric experience with CE [43–48]. Gahukamble and Rakas [43] concluded that pericystectomy was suitable for paediatric practice, while Khursheed et al. [44] compared capitonnage with an open method (tube drainage) to deal with the residual pericyst cavity after the removal of the endocyst and concluded that patients treated with the open method had a more rapid recovery, fewer postoperative complications and a shorter hospital stay. Precisely the opposite conclusion was reached in a retrospective review of 55 children by Celebi et al. [45], who concluded that omentoplasty and capitonnage were more effective than tube drainage in the management of the cyst cavity. There is also increasing experience of treating CE using laparoscopic techniques, although the actual surgery employed tends to be conservative [46].

Morbidity and mortality of hydatid surgery vary between centres, with reports of postoperative mortality of 0%–7%, influenced by type of operation and rate of intra-abdominal complications [49–51]. Deaths have been reported due to anaphylaxis or septic shock, but specific complications include external biliary fistula, infection of the residual cavity, residual hydatid membrane in the CBD and postoperative haemorrhage. Cysts in the dome, the presence of a cystobiliary fistula and intrabiliary rupture of a cyst are all independent predictors of morbidity.

Those procedures associated with lower recurrence rates should probably be deployed where possible, and these include radical procedures (pericystectomy ± liver resection) compared with more conservative options (e.g. simple cystectomy).

5.9.7.2  PAIR

A variety of percutaneous methods are described, the most common of which is puncture, aspiration, injection of a scolicidal agent and reaspiration (PAIR) [47,48,52,53]. PAIR techniques vary as to the scolicidal agent used and use of a needle or a catheter, while others have modified the procedure and use a coaxial catheter system [53,54]. A key factor in this choice is the level of care available and the individual skill of the interventional radiologist. Meticulous preprocedure planning, including discussion of up-to-date imaging at a multidisciplinary team meeting, is essential.

PAIR is not recommended for CE2, as the relapse rate is between 48% and 59% due to the persistence of daughter cysts not punctured during the procedure [48,54]. Surgery or another percutaneous procedure is preferred.

Some critics of PAIR or other PTs for CE cite the risk of anaphylaxis or dissemination secondary to leakage of cyst fluid. Neumayr et al. [55] reviewed the risk of anaphylaxis in PT of CE and identified 5943 procedures on 5517 hepatic and nonhepatic CE cysts. Lethal anaphylaxis occurred in

0.03% of procedures (i.e. 0.04% of treated cysts), and reversible allergic reactions in 1.7% of treatments (i.e. 1.8% of treated cysts). of course, anaphylaxis is not confined to percutaneous methods and also occurs in those treated surgically, or after trauma.

5.9.7.3  SURGERY VERSUS PAIR

A Cochrane review [56] identified only one randomised controlled trial (RCT) of PAIR versus surgery (n = 50) and one of PAIR ± albendazole versus albendazole alone (n = 30). Compared with surgery, PAIR + albendazole resulted in similar cyst disappearance and mean diameter, fewer adverse events and fewer days in hospital. PAIR ± albendazole resulted in significantly more cyst reduction and symptomatic relief.

A meta-analysis [57

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