The commonest extra colonic complication of amoebic dysentery is amoebic liver abscess. In two-thirds of cases they are solitary, the rest are multiple [1], of which some may coalesce to form a single abscess at a later stage.

Case Report

A middle-aged male presented with pain in the right hypochondrium, fever with chills and rigors. A plain X-ray chest revealed an elevated right dome of diaphragm (Fig. 1). An isotope liver scan was performed which showed a photopenic area in the superior portion of the right lobe of the liver (Fig. 2). Ultrasound demonstrated a large hypoechoic area in the postero-superior segment of the right lobe of the liver (Fig.3). CT Scan demonstrated multiple hypodense areas (a total of four) in the postero superior segment of the right lobe of the liver (Fig 4). The diagnosis was confirmed by a positive serological test.

Discussion

The radiological investigations, which may be performed in a suspected case of amoebic liver abscess, are—plain X-ray chest, fluoroscopy, isotope liver scan, ultrasound and CT Scan.

The commonest plain X-ray chest finding is an elevated right dome of the diaphragm, i.e. more than 2.5 cm or more than one intercostal space higher than the left dome). Occasionally a localized bulge or tenting of the right dome of the diaphragm may be seen in a superiorly located abscess. Fluoroscopy confirms these findings and in addition demonstrates restricted mobility of the diaphragm. These findings are non-specific and may be seen in many other conditions e.g. subphrenic collections, subpulmonic effusions, further-more other than the superior surface abscess, plain X-ray and fluoroscopy are not able to localize the abscess.

Isotope liver scan was the first imaging modality to localize an abscess. These appear as cold or photopenic areas. Isotope scans have a high sensitivity in detection of lesions but a very low specificity [5], as they are not able to indicate the pathology; cyst, haematoma, haemangioma, tumour, abscess all appear the same. An ultrasound or CT scan is further required to define the pathology once a cold area is detected on isotope scan. Surface lesions are easier to detect rather than deep lesions.

On ultrasound an amoebic abscess appears as a round, subcapsular, hypoechoic area containing fine echoes which may layer in the dependant portions.[6] In the early stages an amoebic abscess appears as a subtle area of decreased echogenicity. The ultrasound diagnosis is not pathognomonic as complicated cysts, haematoma, metastases and amoebic abscess may resemble with each other.

CT scan appearances are in the form of a well-defined homogeneous, hypodense area, whose Hounsfield units are greater than a benign cyst and less than a tumour [2]; this is not always true, as there may be an overlap. Intravenous contrast defines and highlights the abscess very well. The wall of the abscess is relatively avascular, therefore it does not enhance however the periphery may appear a bit hyperdense due to compressed hyperemic liver parenchyma.

Isotope scans due to their low specificity are at the most used as a screening procedure. Both ultrasound and CT demonstrate and localize the abscess accurately. Although their appearances are not pathognomonic, in the clinical setting of pain in the right hypochondrium and fever, these appearances are adequate to institute therapy. Only serological tests are diagnostic.

The importance in localizing a lesion is for aspiration of an amoebic abscess.

Aspiration may be required for:

1. Making a diagnosis [7] - typical anchovy sauce is aspirated. The pus is usually sterile and a biopsy of the wall is required to identify the organism.
2. When there is rapid clinical deterioration or inadequate response to therapy [7].

In our case both ultrasound and CT detected the abscess, but in a previously reported case [4] apparently only CT discovered the lesions which ultrasound missed. Furthermore, in our case isotope scans wrongly localized the lesion to the superior surface, while ultrasound and CT accurately located it in the postero superior segment. As regards detection of lesions both isotope scan and ultrasound detected one lesion. This increased sensitivity of CT may appear purely academic. However, when it comes to tapping multiple abscesses the largest must be tapped and in a toxic patient as many as possible should be tapped. [3]

Therefore, we conclude that though ultrasound is the modality of choice in management of patients with amoebic liver abscess, CT scan has a greater sensitivity.

REFERENCES

1. Eisenberg: Diagnostic Imaging in Surgery.
2. Haaga J, Alfidi AJ: Computed Tomography of the Whole Body. Publishers Mosby. Vol. 2, 2nd edition 820, 821.
3. Kapoor O.P.: Editorial comment 1988, BHJ. Vol.30, No.3, Pg.89.
4. Kapoor O.P.: Multiple amoebic liver abscess. 1989 BHJ, Vol.No.1, page 127.
5. Sutton David; A textbook of Radiology and Imaging. Pg.1745-1782.
6. Sukougj, Cohen CJ et al: Sonography of Hepatic Amoebiasis. AJR, 1989. 134; 911-915.
7. Van Sonneberg E et al: Intrahepatic amoebic abscess: Indications for and results of Percutaneous Drainage. Radiology, 1985. 156:631-635.