Over 20 members of the ultrasound (U/S) classification network met in Lisbon, Portugal on Thursday 6 th November, 1997 to discuss the classification that had been developed by members of the network over the previous two years.

A further meeting between a few network members took place in Orlando, USA in December. The overall structure and aims of the classification was generally well accepted and agreed upon. There was some discussion on the order of cyst Types as presented and it was felt that this would be decided upon finally following further studies.

Modifications were made to the classification in order to allow a single cyst Type to be classified irrespective of size, but size will be stratified within each Type. The revised classification will also include information of the decade of life the patient was diagnosed by US in order to examine the possibility of examining changes of cyst appearance with age.

The revised classification is presented in the following pages. The details of description of the different types (with US images) will be sent to the participants in The Network only.It is hoped that network members will provide data from their regional studies to the network coordinator to examine geographical variations in the US Types of the parasite. Any such findings will be published by the network as was done with the clinical treatment of echinococcosis.

Introduction

Since the late 1970's ultrasound (US) has been used for detecting pathological lesions due to a number of parasitic infections including cystic echinococcosis (CE) (King, 1973; Vicary et al, 1977; Babcock et al, 1978; Alltree, 1979; Hadidi, 1979; Macpherson, 1992; Palmer, 1995).

US has more recently been used for the examination of cyst development over time (Romig et al, 1986) and as a means of assessing changes of cysts following chemotherapy (Cossetto et al, 1989) and for surveillance in a hydatid control program (Macpherson et al, 1986).

The introduction of portable US scanners in the mid 1980's facilitated the use of the technique in communities and an increasing number of community based surveys have recently been reported from many parts of the world including Tunisia (Mlika et al, 1986; Bchir et al, 1987; 1991) Libya (Shambesh et al, 1992), East Africa (including Tanzania, Kenya, Sudan, Ethiopia) (Macpherson et al 1987; 1989), Uruguay (Perdomo et al, 1988; Frider et al, 1988) and China (Wang et al, 1991: Chai, 1992; Jiang, 1991).

In contrast to radiology, the grading and staging of pathological conditions detected by US is still evolving. A number of classifications for CE have been previously proposed (Gharbi et al, 1981; Beggs, 1983; Lewall and Mcorkell, 1985; Perdomo et al, 1995; Caremani et al, 1997). Without a standardized classification observations made by different investigators in different endemic settings are not directly comparable.

Longitudinal studies to investigate the natural history of the disease or to follow the natural, or artificial degradation of cysts following chemotherapy, cannot be categorized in a comparable manner. Current classifications also need to be modified to provide a simple grading system for use in a clinical setting. Such a grading system will be useful for physicians using currently acceptable treatment regimes (Pawlowski, 1993; 1997; WHO, 1996). There is therefore the need for a standardised classification to facilitate both the uniform reporting of results from field epidemiological studies as well as in clinical studies conducted in different parts of the world. There is some evidence that the pathology of infection resulting from CE varies between different areas and population groups. For example the majority of cysts in Turkana, Kenya are large, unilocular and fertile (Macpherson et al, 1987). A much more benign strain which usually presents as calcified, small infertile cysts are reported from the northern hemisphere (Wilson et al, 1968; Little et al, 1988; Paul and Stefaniak, 1997). Such variations could depend on the time after infection that they are first diagnosed, intra-species variation of the parasite or from a heterogeneity of behavioral host differences which may be immunological, genetic or nutritional. A standardised classification will facilitate the collection of data to examine variations in pathology in different geographical areas of the world. The WHO classification of CE presented here requires evaluation in both the clinical and field settings. Collaborators are requested to complete Tables 1 and 2.

Pathognomonic signs

The following US images of space occupying lesions in the liver are considered to be pathognomonic diagnostic signs of CE due to Echinococcus granulosis.

1. Unilocular anechoic lesions which are round or oval with a clear laminated membrane or with snow like inclusions (Type 2)
2. Multivesicular or multiseptated cysts with a wheel-like appearance (Type 3).
3. Unilocular cysts with daughter cysts which may present with a honeycomb appearance (Type 3).
4. Cysts with floating laminated membranes which may also contain daughter cysts (Type 4).

Variations in the prevalence of space occupying lesions due to factors other than CE will complicate the accurate diagnosis of CE by US, particularly in low CE prevalence areas (Macpherson, 1992; Stefaniak, 1997 von Sinner, 1997). It is essential for investigators to report the number of space occupying lesions detected, the number of suspected CE cases and the number confirmed from both clinical and field based settings (Table 2).

Clinical and laboratory data play as large a role for the correct diagnosis of CE as does ultrasonography, and US results should be evaluated in relation to these findings. Correlation between US and several other diagnostic techniques may not be possible, depending on the availability and quality of facilities in any endemic setting. For a definitive diagnosis of CE in US detected CE images, which have no visible pathognomonic signs, need to be confirmed using one or more alternative diagnostic method. The detection of protoscoleces or hooks on biopsy or from surgical material provides a definitive diagnosis. Fine needle aspiration biopsy (FNAB) can detect specific antigen even in sterile cysts (Stefaniak, 1997). Immunological tests (Craig, 1997), molecular biological techniques (Lightowlers and Gottstein, 1995) also add certainty to a diagnosis. Other non-invasive imaging techniques, for example, CT or MRI are also useful (von Sinner, 1997).

An important component of US surveys in hospitals and the field are the identification of patients at severe risk from the cysts detected that may require urgent intervention. Such patients may present with existing complications: cysts communicating with the biliary tree, exerting pressure on vital organs or infected cysts. Others may present with a risk of future complications: cysts that may rupture spontaneously or due to trauma, such as large superficial cysts or cysts that may lead to pressure complications.

It is also important to record the biological status of the cysts as revealed by US. These may be classified as active (Group 1: Types 1, 2, 3), transitional (Group 2: Type 4) or inactive (Group 3: Types 5, 6) which may influence the choice of treatment (Table 1).

Since current scanners generally produce consistent images, the equipment used does not often contribute to variant results. Types of equipment should always be clearly described and its reliability in the field should be reported. Further studies are needed regarding variation between different investigators as well as between different observations by the same investigator at different times. It would also be useful to identify which observations made with the same technique are most frequently subject to variation and to best gauge how the source of this variation can best be avoided.

It is important to evaluate the WHO classification in both the clinical and field based settings. In particular its usefulness, appropriateness and ease of use in the different settings. Collaborators are encouraged to evaluate this classification by completing Tables 1 and 2 and sending them with their comments to the network coordinator. ConclusionsThe widening use of US in both health care centers and for community based surveys for the diagnosis of CE necessitates the development of a standardised classification which will facilitate comparative studies from different endemic settings. The classification proposed here by the WHO network took into consideration the most commonly used previous classifications. The classification follows the known natural history pattern of the disease (active, transitional and inactive groups) which will be helpful in a clinical setting. Comparative clinical and field based studies from various parts of the work will help in examining variations in the natural history and possible geographic differences in the parasite. US users in both clinical and field based studies on CE are encouraged to use the proposed standardised classification system as soon as possible.

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The following WHO classification system is proposed by the network participants and is related to the most commonly used previous classifications.

Location ............................. Clinical\Field study? ............................. Dates of survey(s) ..................................

Investigator (s) ......................................................................................................................................................

Table 1: Summary of data. Cyst Types and sizes S (small cysts <5.0 cm), M (medium cysts 5 - 10 cm), L ( large cysts >10 cm), and decade of life in which they were first diagnosed by US.

 Type of Cysts

Total number of space occupying lesions seen ..............

For Types 1, 5 and 6 where pathognonomic signs for CE with US are not found please complete Table 2 below.

Table 2: Differential diagnosis of US suspected CE lesions

Please complete Tables 1 and 2 following the completion of the US survey. If you would like to collaborate with the WHO network on US classification for CE please send the information to the network co-ordinator (Calum Macpherson, P.O. Box 7, St. George's, Grenada, West Indies: Tel: 1 473 444 3068; Fax: 1 473 444 3041; email calum_macpherson@sgu.edu ). The results will be published by the US network and your contribution will be acknowledged. If you have any difficulty with filling in this form or would like to provide further information please contact Calum Macpherson.

Very many thanks for your help.

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