In the last few years, radionuclide liver scanning has been available as an imaging device, wherein an abscess is seen as a cold area. The size of the abscess does not always correspond with the dimensions of the cold area. The reason is that a zone of congestion surrounding the abscess (Fig. I) also does not pick up the isotope, and gets added to the original size of the abscess. With better radionuclide photon flux with technetium, one can see the zone of hyperaemia surrounding the abscess. [2]

Since the advent of radionuclide liver scan, it has become possible to firmly establish the diagnosis of liver abscess; furthermore, we are diagnosing multiple abscesses much more frequently. This has great bearing on the management of the patient. It has happened in olden days that a patient, diagnosed as having all inferior surface amoebic liver abscess, had the diagnosis confirmed at the operation table, the abscess was drained, and yet the patient died in the postoperative period because of the presence of a second, huge, intrahepatic superior surface abscess, which was missed by the surgeon. Today this will not happen, thanks to the availability of radionuclide liver scan. But if the abscesses are multiple and so many that there is hardly any normal liver tissue then isotope scanning with older agents like 1-131 Rose Bengal may not show any cold areas. Then sonography will be a more useful investigation

Similarly, if the abscesses are solid ( Fig. 2 ), ultrasound cannot furnish a diagnosis of amoebic liver abscess. Perhaps one will have to depend on the clinical history and serological tests, if no pus can be aspirated from a cold area (Fig. 3).

The diagnosis of amoebic liver abscess depends on its site: where it is located e.g. superior surface, inferior surface, left lobe, right lobe and their various segments ( Fig. 4 ) .

In the past, we had depended mainly on radiology as an imaging device. Quite often a pneumoperitoneum was done to demonstrate a tract between the liver abscess and the chest (Fig. 5). Since it is so readily available to everyone, Radiology still re mains one of the useful imaging devices to see an amoebic abscess as long as we appreciate its limitations. All of us are familiar with the appearances of the right dome of the diaphragm in a patient having symptoms of amoebic liver abscess (Fig. 6a). These appearances are all suggestive of a "superior" surface amoebic liver abscess of the right lobe; of course, one is not actually visualising the abscess. If an abscess has to be visualised, the imaging device should be the radionuclide liver scan. Fig. 6b shows all abscesses in the superior surface of the liver. When a liver scan is done using Te99m sulphur colloid, this radiopharmaceutical has an added advantage in that one can also diagnose transient portal hypertension if it is present, in a patient having all amoebic liver abscess (Fig. 7).

Once in a way, when we diagnose a superior surface amoebic liver abscess from the radiological appearances (Fig. 8a), you will be surprised to see that on the isotope scan, the abscess is not located superiorly but is in the middle of the posterior surface (Fig. 8b). This is important information for the clinician because these abscesses should be tapped from behind. In addition, if you see a markedly elevated right dome which is clean and with a normal costophrenic angle, it is worth remembering that it may be due to a huge inferior surface amoebic liver abscess.

Sonography is another method of imaging where not only a pathological (cold) area can be seen but one can distinguish a solid (sonic) from a fluid filled area (sonoluscent).

Laparoscopy offers much more advantage in that you can see an abscess with your naked eye. Although it is an invasive investigation, it is one of the best examinations for visualising an abscess. Not only that but the differential diagnosis of an abscess from conditions like malignancy can be made with elegance (Fig. 9). One can also take an open biopsy. We have seen polycystic liver very well demonstrated by this investigation, when the ease was mistaken for an amoebic abscess.

It is worth knowing that superior surface liver abscesses can be better visualised with laparoscopy than at laparotomy. The reason is that at laparoscopy the air insufflation exposes the whole superior surface.

One can establish with radionuclide scanning and sonography and laparoscopy an abscess in the liver. It cannot be labeled as "amoebic" abscess unless you demonstrate Entamoeba histolytica. At autopsy, this parasite could be shown under the microscope in the liver biopsy taken from the edge of the abscess (Fig 10). In practice, one has to demonstrate this in the aspirated pus. It is the terminal portion of the pus in which this parasite should be looked for, within seconds after aspiration. When this procedure fails to reveal the parasite, one has to rely only on serologic tests e.g. indirect haemagglutination test ( IHA ). A positive test in a high dilution, e.g. 1 in 1024 or 2048 is diagnostic of "amoebic" liver abscess. What is the role of the whole body CAT scanner in the near future? In my opinion although computerized tomography can resolve lesions smaller than 2 cm or lesions in depth which may be missed by radionuclide scanning, it will not have a very big role to play in the diagnosis of amoebic liver abscess. By the time this investigation becomes generally available, computerized real time sonography will have a lot more to offer in the diagnosis of this disease.

I will now discuss the limitations of radionuclide scanning. In majority of the patients superior surface abscesses in the right lobe will have no problem in visualization. At other times there are difficulties which could be experienced. We have seen a patient who was running fever, complained of pain in the right shoulder, had a past history of dysentery and a positive history of alcoholism. He has a positive IHA test in a titer of 1:2048 and his chest x-ray appearance was compatible with a superior surface amoebic liver abscess (Fig. 11a). However no clear cut cold area could be seen on the liver scan, although an area of decreased tracer concentration could be seen (Fig. 11 b) . This patient was ultimately operated upon and in addition to a small pleural aspirate, brown pus was located in a superior surface liver abscess. In another patient a diagnosis of superior surface amoebic liver abscess was made based on history and physical signs. Though x-ray chest was in favor of this diagnosis, scan did not show a clear cut cold area. After some pleural fluid was aspirated, at a space lower down 20 cc of thick brownish pus was located. Yet another lady was admitted in intensive care unit because she had collapsed following massive melena. Since she was running fever for the previous one month, diagnosis of enteric was made. When at routine chest x-ray was done in the ICU it was found that the right dome of diaphragm was markedly elevated and the costophrenic angle was obliterated (Fig. 12a). Diagnosis of superior surface amoebic liver abscess was then entertained. Sigmoidoscopy showed amoebic ulcers which were bleeding. IHA test was positive in a dilution of 1:2048. But the scan did not show a clear cut cold area (Fig. 12b, c). Aspiration revealed 300 cc of typical brownish pus consistent with the diagnosis of an amoebic abscess.

Why was a cold area not seen on the liver SCLII1 in the above patients? One of the explanations could be that in these patients the abscess was superficial and bulging out from the superior surface and was not intrahepatic. We have seen such abscesses at autopsy. Liver scan may miss superficial but not intrahepatic abscesses (Fig. 13).

Recently, we have also seen "false positive" cold areas in the superior surface on the liver scan. Fig. 14a shows an x-ray chest with a right sided shadow consistent with the diagnosis of right sided pleural effusion. This was in a young man where there was a positive history of tuberculosis in the family. But since he was also complaining of symptoms of dysentery of one week's duration, routine liver scan was asked for. A concave dent along the upper posterior border of the liver was seen in all the views and was interpreted as being compatible with an abscess on superior surface which has burst into the pleura (Fig. 14b). Pleural tapping revealed 7()0 cc of straw coloured fluid and on probing in the lower intercostal spaces no pus could be drawn. Within 24 hours the scan was repeated. The "cold area" had disappeared dramatically (Fig. 14c). It is a well known fact that cold areas due to amoebic liver abscess disappear over two to three months period. This was false positive cold area in the superior surface. At J. J. Hospital we have collected a large series of such patients i.e. patients with moderate and massive pleural effusions who have got cold areas in the superior surface seen on liver scans. Some of these patients of moderate pleural effusions have also in addition to cold areas, a poor uptake of the isotope (Fig. 15, 16). This should be kept in mind while making a diagnosis of superior surface abscess, especially in patients having fluid in the right pleural cavity.

Which other imaging device can diagnose superior surface amoebic liver abscess better than isotope scanning? What about sonography? Unfortunately, sonography is a poor investigation for superior surface amoebic liver abscess. This is because when the transducer is placed on the right lower chest the ribs are a hindrance to the sound waves. Therefore, sonography is a useful investigation more for inferior surface liver abscesses. Also false positive sonoluscent areas can be seen. Fig. 17a shows a sonoluscent cold area reported in the superior surface of the liver in a patient with vague abdominal pain. This patient had a normal liver scan (Fig. 17b). He had no abscess in the superior surface.

What are the advantages of sonography in diagnosis of amoebic liver abscess as compared to isotope liver scan? These are as under:

1. It call demonstrate that the cold area is sonoluscent which means it contains fluid.
2. It call pick up an abscess which is less than 2 cms which call be missed by isotope liver scan.
3. Diaphragmatic movements can be measured accurately. Diaphragm can be located even in patients with a shadow on the right base, where on x-ray chest it is impossible to visualise the dome (Fig. 18).
4. The differential diagnosis of amoebic liver abscess from hydronephrosis, biliary calculi or empyema of the gall bladder, acute alcoholic fatty liver and right-sided pleural effusion can be made at the same sitting.
5. There are conditions where the isotope liver scan may not help you in the diagnosis of amoebic liver abscess. These are multiple small amoebic liver abscesses, superficial amoebic liver abscess, inferior surface liver abscess and patients having an amoebic liver abscess with a poor liver function. For all these patients sonography is a very useful investigation.
6. Sonography can pick up the complications of rupture of left lobe abscess into the pericardium or a right lobe abscess into the pleura.
7. IVC obstruction, obstruction or thrombosis of the hepatic vein or presence of free fluid in the peritoneal cavity, in a case of amoebic liver abscess can be picked up by sonography (Fig. 19).
8. Academic aspects of amoebic liver abscess like solid amoebic liver abscess, the process of healing etc. These subjects cannot be studied without the help of sonography.
9. The most important advantage of sonography is therapeutic tapping. Tapping of amoebic liver abscess can be done most scientifically and confidently, by the help of sonography. In fact in patients having multiple amoebic liver abscesses the prognosis has recently improved, because of the easy tapping of all abscesses in these patients. These patients have usually one or two big abscesses and the rest of them small abscesses. In fact you can measure the sonoluscent area and calculate the amount of pus, which will be expected in this abscess.
10. This investigation has no radiation hazards, hence it is very safe in children and pregnancy.
11. It is a very useful investigation in the differential diagnosis of PUO when in addition to an amoebic liver abscess one can pick up many other causes of PUO.
12. In big institutions it is important to realize that this investigation is not dependent on the usual isotope supply. Finally, in my opinion sonography has a great future especially when the real time system units are available. Also it will be very useful especially in rural areas when portable sonography units will be available.

What are the other investigations in confirming the diagnosis of amoebic liver abscess? What about pus? In the past all of us have observed that chocolate coloured pus is quite diagnostic of amoebic liver abscess. Quite often, pus is reddish in color and more red towards the terminal part of the aspiration. Often in a single sitting of aspiration, by changing the direction of the needle we have aspirated 3 different types of pus. Therefore any coloured pus can be obtained from an amoebic liver abscess.

In one of our patients brown pus was aspirated from the right pleural cavity (Fig. 20a) and because of the color of the pus the patient was diagnosed as possibly having amoebic complication of liver abscess. But on the isotope liver scan, no cold area was seen (Fig. 20b). IHA test was negative. Klebsiella were grown on the culture of this pus. This patient responded to antibiotics and repeated aspirations of the right pleural cavity. While in another patient where amoebic abscess was suspected and liver scan showed a cold area, brownish pus was aspirated and he was labeled as amoebic liver abscess. This patient turned out to have hepatoma of the right lobe of the liver where this pus was not amoebic pus but necrotic liver tissue. Yet on another occasion where a confident diagnosis of amoebic liver abscess was made and isotope liver scan showed a cold area, aspiration revealed no pus, but it revealed a light brownish fluid. We have labeled this as "amoebic fluid". Often in this brownish fluid, you may see floating necrotic liver tissue particles.

Therefore demonstration of any pus by itself from a suspected ease of amoebic liver abscess, by itself is not diagnostic of this disease. What is more important is demonstration of Entamoeba histolytica in the pus or amoebic antigen in the pus. In the absence of this (and the above is possible in only about 25% of the patients) one has to rely on serological tests like IHA test to confirm the diagnosis.

PLEURO-PULMONARY AMOEBIASIS

I will now discuss the relationship between amoebic liver abscess and pleuro-pulmonary amoebiasis. There are 2 types of pleuro-pulmonary amoebiasis. The first type is one which is familiar to everybody. The patient is a known case of superior surface amoebic liver abscess and later on he develops a pleuro-pulmonary complication In these patients the X-ray chest shows an elevated dome of diaphragm. Any shadow seen in the right chest in such a patient will remind one to think of pleuro-pulmonary complication. Huge liver abscess in such cases can be easily spotted on radionuclide liver scan. But we had an occasion when there was pneumonia (amoebic) and at the autopsy the patient had multiple abscesses not in the superior surface but lower down, some less than 2 cm and solid (Fig. 21). In such a case how could these amoebic abscesses be thought of and picked on isotope liver scan? In a similar case (Fig 22) is shown an amoebic abscess in the apex of the right lung and yet this patient on autopsy had a small superior surface abscess about 2 dm in diameter in the liver.

Ten years back a patient was admitted in my ward with a pyrexia on one month duration and cough of one week’s duration. One week prior to the admission, his X-ray chest was obtained (Fig 23a). Looking at the right dome you would never have suspected that this patient was brewing a superior surface liver abscess. The diaphragm was absolutely normal and was in fact flat with a normal costophrenic angle. There was a shadow in the left upper zone consistent with the diagnosis of old healed Kochs lesion. In the wards, after a week the patient developed pain in the right chest. X-ray chest was repeated. Multiple cystic shadows were seen at the right base with obliterated costophrenic angle (Fig 23b). After a week the same shadow increased (Fig 23c). Right pleural cavity was tapped and yellow coloured pus was aspirated. Before the culture report was available, the patient died. At autopsy an empyema and amoebic pneumonia were seen in the right hemithorax. An amoebic abscess was present in the liver. We learnt a great lesson. In our country, if one wants to diagnose pleuro-pulmonary amoebiasis, high index of suspicion is the most important point in making a diagnosis of superior surface amoebic liver abscess.

Figs 24, 25, 26, 27, 28 show the chest x-rays of some of the patients showing vague shadows at the right base. Pleuro-pulmonary amoebiasis was thought of in these patients. In some of them once the pleural aspiration was done, we probed for locating pus in the liver as well. In others it is the sputum which has helped in the diagnosis. Brownish coloured sputum with presence of Entamoeba histolytica in the sputum is diagnostic. Serological tests are also very helpful in the diagnosis of pleuro-pulmonary amoebiasis. In fact, if a patient in our country has got some symptoms and a shadow in the right chest, and if the IHA teat is positive in a high dilution then an isotope liver scan must be asked for. Then you are also in a better position to identify false positive and false negative cold areas on the liver scan. In most of our patients cold areas were seen on isotope liver scan.

Acknowledgment

I am very thankful to S.S. Publishers for allowing me to reproduce all the figures in this paper.

References

1. Kapoor O.P. : Amoebic liver abscess : Monograph. S.S. Publishers, Bombay, 1979 p.108
2. Lele RD and Nagarwala HK. Radionuclide liver scanning. Bulletin of the Jaslok Hospital & Research Centre 2, 262, 1978.