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Ultrasound, CT and MRI of ruptured and disseminated hydatid cysts
European Journal of Radiology, 11 (1990)
31-37
Elsevier
31
EURRAD
00062
Ultrasound, CT and MRI of ruptured and disseminated hydatid cysts W.N. von Sinner Department of Radiology, King Faisal Specialist Hospital, and Research Centre. Riyadh, Saudi Arabia
(Received 22 November
1989; accepted
after revision 28 March 1990)
Key words: Hydatid disease, CT; Hydatid disease, MRI; Hydatid disease, ultrasound
study; Radiography,
hydatid disease
Abstract
Three cases of echinococcus granulosus with rupture of hydatid cysts and widespread abdominal, pelvic or pleural dissemination are described. Ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) allowed recognition of ruptured hydatid cysts. This assisted to come to an appropriate therapy and exclusion or confirmation of hydatid cysts elsewhere in the body. Ultrasound, CT and MRI are also important for follow-up, evaluation of therapeutic response and/or early diagnosis of recurrence.
Introduction Echinococcus granulosus is endemic in many sheepand cattle-raising countries throughout the world. Delayed diagnosis is common, and often results in spreading of the disease. Unrecognized hydatid cysts may become very big and rupture. Anaphylactic reactions include life-threatening shock. Abdominal, pelvic and pleural dissemination due to discharge of parasitic contents may follow, causing growth of innumerable daughter cysts excluding curative surgery. Modem imaging modalities, such as ultrasound, computed tomography and magnetic resonance imaging are helpful in diagnosing the disease and making effective therapy possible. I have observed a number of ruptured hydatid cysts with dissemination and would like to publish the experience with these cases. Material and Methods The cases of hydatid disease with abdominal, pelvic and/or pleural dissemination secondary to rupture of hepatic or splenic hydatid cysts are described. Address for reprints: Dr. W.N. von Sinner, Department of Radiology, King Faisal Specialist Hospital, P.O. Box 3354, Riyadh 11211, Saudi Arabia. 0720-048X/90/$03.50
0 1990 Elsevier Science Publishers
Ultrasound, CT and MRI were used in all cases, allowing correlations with these imaging modalities. Ultrasound examinations were obtained with an SDR 1500 sector scanner (Picker) and Acuson scanner. CT scans with and without contrast enhancement were obtained using a Somatom DR3 (Siemens), and MR imaging was performed with a 1.5 Tesla machine (Picker) using Tl and T2 conventional spin echo techniques with the following parameters, TR = 850 ms, TE = 20 ms, TR = 2000 ms and TE = 100 ms. The examinations were performed in transaxial, coronal and sag&al planes. Case reports Case 1 A lPyear-old male was referred to our hospital with abdominal pain. The physical exam showed multiple ‘tumors’ in the liver, spleen and abdomen. Ultrasound showed complex cystic changes with a double-line sign suggestive of collapsed parasitic membranes (Fig. la). CT documented widespread involvement of spaceoccupying lesions throughout the abdomen (Fig. lb) and pelvis (Fig. lc) including the peritoneal and retroperitoneal spaces. The indirect hemagglutination (IHA) test was highly positive (1 : 4048). Laparotomy confumed the presence of a large number of hydatid cysts of which many were removed during surgery. Pathology confirmed the presence of scolices. High-dose meben-
B.V. (Biomedical
Division)
32
Fig. 1. Case 1: a 19-year-old male with multiple abdominal and pelvic hydatid cysts. (a) Abdominal ultrasound: complex hepatic cystic changes with double-line structures representing collapsed parasitic membranes (arrows). (b) CT (without contrast enhance-
ment): multiple abdominal hydatid cysts. (c) CT of pelvis (without contrast enhancement): large number of pelvic hydatid cysts. (d) Tl weighted MR image, coronal view, right side, (TR 850 ms, TE 20 ms): ruptured hydatid cyst with peritoneal spillage (black curved arrows). Observe also prolapsed hydatid cyst into right lung base from right liver lobe (straight black arrows). (e) T2 weighted MR image axial view, right side (TR 2000 ms, TE 100 ms): ruptured hydatid cyst with discharge of cystic contents and peritoneal spillage (large straight black arrows). Observe also low intensity rim (small black arrows) and pericystic reaction with edema (curved open arrows).
33
dazole treatment for several months was only partially effective. Most cysts persisted or had increased in size, especially those in the liver and spleen. One liver cyst had ruptured spontaneously, and showed disrupture of the cyst w’all and a low intensity rim with discharge of cystic contents into the peritoneum (Fig. 1 d and e). High-dose albendazole was started. Two months later spectacular regression of most cysts was noted with remarkable improvement in the patient’s condition. Case 2 A lo-year-old male was admitted to our institution who was known to have hydatid disease of the liver. Four years ago, he was re-admitted for recurrent hydatid cysts of the liver. The IHA test was 1 : 2026 (normal 1 : 32). He was re-admitted for a third time 2 years ago. An exploratory laparotomy was performed with the removal and in situ therapy of multiple hydatid cysts after mebendazole treatment had been unsatisfactory. Ultrasound and CT of the abdomen showed multiple hydatid cysts of the liver, the spleen (Fig. 2) and pelvis. The pelvis contained two large cysts, one above the bladder and one deep in the right pelvic fossa associated with a cluster of smaller hydatid cysts in the same area measuring approximately 2-3 cm in diameter each. In addition, many small cysts unattached to organs were found in the retroperitoneum and omentum. Pathology confirmed the presence of hydatid cysts of the liver, spleen and pelvis containing parasitic membranes and scolices.
Fig. 2. Case 2: a IO-year-old male with hydatid disease. CT of abdomen (with barium contrast in stomach) showing hydatid cyst of liver and spleen (with small calcification of the wall) in close relationship to the stomach (arrows).
Case 3 A 40-year-old male presented with abdominal-space occupying lesions known to be caused by multiple hydatid cysts. His history began 5 years ago when he noticed a swelling in his upper abdomen. Two years later he was involved in a traffic accident and his swellings suddenly disappeared. One year after the accident he again noticed abdominal distension. At surgery, hundreds of small hydatid cysts were removed from the abdomen. Pathology confirmed hydatid disease. Mebendazole treatment was carried out for 3 years, with unsatisfactory results. 4 months ago, the patient presented again with new swellings in the abdomen. In his past history there was an episode with jaundice and abdominal pain. The physical examination revealed a large smooth non-tender mass in the right hypochondrium about 8 x 8 cm in size, and also a smaller mass in the left hypochondrium. A third mass in the right lumbar region was not mobile. A non-enhanced and contrast-enhanced dynamic CT showed further increase of some cysts with imminent rupture (Fig. 3a). Three weeks later ultrasound and MRI showed detachment of parasitic membranes, demonstrating the ‘serpent or snake sign’ which is pathognomonic for hydatid cysts (Fig. 3b, c and d). Following surgery he made a good recovery. Discussion After the eggs of Echinococcus granulosus are freed from their coating by digestive enzymes, larvae penetrate the mucosa of the jejunum, reaching venules and lymphatics ; they are carried through the portal circulation into the liver where 50-70x are filtered out. Another 30-40% reach the capillary filter of the lungs, via the inferior vena cava, and only lo-20% arrive in the systemic circulation from which they may be distributed to all organs and tissues of the body. Many larvae die during the passage or when they get stuck in the filters resulting from the host’s defence mechanisms. Those who survive transform into cysts. Their wall differentiates into two layers, the so-called ectocyst consisting of a hyaline membrane, supporting the endocyst (germinal layer) which generates scolices, brood capsules and daughter cysts; they may be pinched off into the central fluid containing area and fall to the bottom of the cyst as ‘hydatidsand’. The host reacts with the formation of an adventitial layer (pericyst) segregating the body from the parasite, consisting of fibroblasts and blood vessels through which the parasite receives nutrients. After 6 months the hydatid cyst reaches a diameter of 1 cm and thereafter grows every year 2-3 cm without
Fig. 3. Case 3: a 40-year-old male with multiple hydatid cysts of the abdomen. (a) CT of abdomen, right side: without contrast enhancement. Large hepatic cyst showing defective posterior cyst wall (white arrows) with low intensity rim (black arrows). (b) Ultrasound of abdomen, right side, showing ‘serpent’ or ‘snake’ sign; cyst wall (black arrow) collapsed parasitic membranes (white arrow). (c) Tl weighted axial MR images, right side, (TR 850 ms, TE 20 ms) demonstrating ‘serpent’ or ‘snake’ sign (arrows). (d) T2 weighted axial MR image, right side, (TR 2000 ms, TE 100 ms) demonstrating ‘serpent’ or ‘snake’ sign (arrows).
35
initially causing symptoms. Most patients are infected in their childhood. It takes years for the hydatid cyst to reach a substantial size [l-20]. Vital structures may then be affected and vague symptoms may arise depending on the location of the cyst, the organ affected and the type of vital structures involved. In the asymptomatic period, Echinococcosis may be discovered by conventional radiographs if the cysts are calcified [ 2,3,4]. Uncalcified cysts are usually demonstrated by ultrasound [2,7], CT [3,5,10] or MRI [4-61. In the early stages their appearance may be uncharacteristic. A ‘double line’ is not infrequently found in unruptured hydatid cysts (Fig. la) [22]. If present, hydatid cysts can be differentiated from simple cysts, cystic tumors, metastases, abscesses etc. Serologic tests [ 191 may be helpful in confirming a suspected diagnosis. However, the usual intradermal tests (Casoni) and Weinberg’s complement fixation test have been evaluated by many authors to be unreliable, because of false-positives or false-negatives of the former, and possible negative results of the latter. Moreover, patients with other helminthic diseases, particularly schistosomiasis, may have false-positive results. Modern tests such as the IHA test and latex agglutination test are more reliable; but even these may have false-positive or false-negative results. The presence of ‘arc 5’ in a recently described immunoelectrophoresis is more promising for diagnosis of Echinococcus but its wide use is limited due to technical reasons. With the expansion of the spaceoccupying lesion, a bulge in the liver or spleen may stretch the capsule, causing pressure atrophy and necrosis [ 5,201. This may lead to a small dissection of the pericystic and/or the parasitic layers, bleeding of blood vessels, erosion of bile ducts, and finally to a frank rupture of the capsule and of the parasitic germinal layers (endocyst and/or ectocyst) [ 7,8]. The fluid pressure in the hydatid cysts in quite high, and, as a consequence, the fragile parasitic membranes may split and small dissections may occur through which parasitic fluid may evade into the virtual space between the pericyst and the ectocyst, causing detachment or collapse of the parasitic membranes. If air is entering from the outside through defects in the pericyst, such as may occur if bronchioles, bile ducts or air-containing organs are eroded, air may enter the space between the pericyst and ectocyst leading to detachment of the parasitic membranes, as has been described in pulmonary hydatid cysts (sign of detachment or crescent/meniscus sign; ‘water-lily sign’). Small amounts of parasitic liquid may evade through these small defects and be discharged into the blood vessels or the peritoneum of the patient. If the patient is sensitized against the foreign
proteins of the hydatid fluid, hydatid sand or daughter cysts, anaphylactic reactions or shock [ $12,161 and dissemination may ensue [ 131. The increasing size and age of the cysts, may lead to areas of degeneration of the cystic membranes and production of brood capsules and daughter cysts, and spontaneous detachment of the parasitic membranes. Degeneration by aging or trauma, toxins, chemotherapy or lack of nutrients, may lead to damage of the cystic wall with an increased risk of rupture. Recently, a low intensity rim thought to represent the pericyst has been described surrounding hydatid cysts of the liver (Fig. le) [4]. We have confirmed its existence on T2 weighted MR images, not only in liver cysts but also in hydatid cysts of the thoracic wall the lungs [ 51, where they may be more marked due to the compression of lung parenchyma, atelectatic tissue and secondary allergic reactions against the parasite. If the cyst is surrounded by normal lung parenchyma, this low intensity rim may be difficult to detect. Usually the place where the cyst is abutting on the thoracic wall can be clearly seen. A defect in the pericyst (adventitial layer) may be demonstrated on CT (Fig. 3a) and/or MRI imaging (Fig. le). On MRI [ 5,6,8] recognition is easier on standard Tl and T2 conventional spin-echo techniques in different planes (axial, coronal, sagittal and intermediate planes). Undulated membranes are rarely seen on ordinary radiographs but are pathognomonic for hydatid disease on ultrasound, CT and MRI, having the appearance of a ‘snake’; therefore, I call this pathognomonic sign the ‘serpent’ or ‘snake’ sign (Fig. 3b, c and d). Although the appearance of collapsed membranes on conventional radiographs and ultrasound has previously been described and occasionally been mentioned on CT, to the best of my knowledge, no previous publication has been found identifying it on MRI. There are also differences in the ‘water-lily sign’, described since collapsed membranes are floating on fluid. In our cases the importance of this ‘serpent’ or ‘snake’ sign as a pathognomonic sign allowing confident diagnosis of hydatid disease could be clearly demonstrated (Fig. lc, d and e). It has not been shown to occur in any other disease or disposition. In the actual event that a hydatid cyst ruptures, this may be accompanied by allergic phenomena, such as urticaria, asthma, collapse or even anaphylactic shock [ 161, in addition to abdominal pain pointing to an acute abdominal event. Expanding cysts may show erosion of the cystic wall, suggesting imminent rupture (Fig. 3a). A defective low-intensity rim on MRI, as demonstrated in Case 3, confirms rupture of the cyst. Following rupture, a ‘serpent’ or ‘snake’ sign may be demonstrated on ultrasound, CT and MRI (Fig. 3a, b and c). The actual
36
event of cystic discharge as a result of spontaneous silent rupture of the wall of the bulging hydatid cysts can as such also be visualized (Fig. Id and e). Such a discharge of cystic contents may generate abdominal and pelvic daughter cysts by peritoneal seeding (Fig. lb and d) [ 13,151. Albendazole treatment appears to be prophylactically and therapeutically effective. Growing hepatic and splenic cysts may also cause pressure atrophy of the diaphragm with prolapse into the lung parenchyma (if adhesions are present) (Fig. Id) or into the pleura (if there are no adhesions) causing secondary pleural dissemination if rupture occurs [ 5,9,1 I]. Rupture of a hydatid cyst predisposes infection of the cyst. If rupture into the pleural space occurs, pneumothorax, pyopneumothorax or a life-threatening tension pneumothorax [ 81 may follow. The exact frequency with which infection of hydatid cysts or of the neighboring tissues occurs is unknown and a matter of controversy. Some authors [21] regard this as a relatively rare event. Others [ 2,7,8,1 l] have observed it rather unfrequently. Based on my preliminary data, infection of ruptured hydatid cysts appears to be relatively common. In my own experience there are three main mechanisms of infection: (1) infection of the cyst due to damage of the pericyst, leading to abscess formation. The diagnosis in these cases is often missed, since it is usually diagnosed as a pyogeneous abscess; (2) rupture of a hydatid cyst with leakage of hydatid fluid causing allergic reaction of the pericystic tissue accompanied by edema (Fig. le). The damaged tissue may be invaded secondarily by bacteria or other agents, leading to a real secondary inflammation; (3) infection of residual or retained hydatid tissue or membranes. Imaging by ultrasound, CT or MRI, may be helpful in clarifying the situation. The demonstration of air bubbles or gas within the lesion and contrast enhancement (e.g., ring enhancement) on CT are strong indicators of infection and abscess formation. Several reports of successful drainage of hydatid infected cysts have appeared in the literature [ 17,181. If a hydatid cyst ruptures into vascular structures, secondary vascular dissemination may ensue. Some cases have been observed where a splenic hydatid cyst had ruptured into other organs, such as the stomach or the left kidney or the colon (see close relationship with these organs as demonstrated in Fig. 2). If viable material containing a large number of viable larvae is discharged into the stomach secondary infection may occur. Growing secondary cysts in the small pelvis may also lead to compression of the bladder and ureters causing obstruction of the urinary pathways leading to bilateral hydronephrosis [ 14,151. Ultrasound, CT and MRI play a keyrole in
diagnosing and monitoring surgically or chemotherapeutically treated disseminated hydatid disease. They are of great help in excluding or confirming any other hydatid cysts locations in the chest, brain or elsewhere in the body. Recurrence of hydatid cysts can easily be detected by CT and MRI before they have spread to other areas or caused deterioration of the patient’s condition. In chemotherapeutically treated patients (e.g., with albendazole), the progress or the improvement of the hydatid disease can be periodically followed until its total resolution. The significance of this study is based on: (1) A new pathognomonic sign that can be identified on Tl and T2 weighted MR images, called the ‘serpent’ or ‘snake’ sign and which allows the specific diagnosis of hydatid disease. Other signs of hydatid disease, such as ‘low intensity rim’ or ‘daughter cysts’ may be helpful and assist in the diagnosis, but are not pathognomonic ‘per se’. (2) Ultrasound, CT and MRI are useful in recognizing rupture and other complications of hydatid cysts. They may exclude or confirm the presence of other hydatid cysts elsewhere in the body. (3) Recognition of ruptured hydatid cysts by ultrasound, CT and MRI is important for appropriate therapy. (4) In abdominal, pelvic or pleural dissemination, where curative surgery is not possible, albendazole therapy may lead to a significant regression of the hydatid disease, as has been documented by ultrasound, CT and MRI. Acknowledgement I wish to express my appreciation to Miss Catherine Devane for her skilful secretarial assistance. References Beggs L. The radiology of hydatid disease. AJR 1985; 15: 639-648. Lewall DB, McCorkell SJ. Hepatic echinococcus cysts: sonographic appearance and classification. Radiology 1985; 155: 113-715. Haertel CF, Fretz CH, Fuchs WA. Computed tomography in the diagnosis of echinoccosus (in German). ROEFO 1980; 133: 164-170. Hoff, FL, Aisen AM, Walden MR, Glazer GM. MR imaging in hydatid disease ofthe liver. Gastrointest Radio1 1987; 12: 29-42. v. Sinner WN, Rifai A, te Strake L, Sieck J. MR imaging of thoracic hydatid disease; correlation with clinical findings, conventional radiography, ultrasound, CT and pathology. Acta Radio1 (Diagn) 1990, in press. Morris DL, Buckley J, Gregson R, Worthington BS. MR imaging in hydatid disease. Clin Radio1 1987; 38: 141-144.
37
7 Lewall DB, McCorkell SJ. Rupture of echinococcal cysts: diagnosis, classification and clinical implications. AJR 1986; 146: 391-394. 8 Lupetin AR, Dash N: Intrahepatic rupture of hydatid cyst: MR findings. AJR 1988; 151: 491-492. 9 Yacoubian HD. Thoracic problems associated with hydatid cyst of the dome of the liver. Surgery 1976; 79: 544-548. 10 Kalovidouris A, Pissiotis C, Pontifex G, Gouliamos A, Penken S, Papavassilion C. CT characterization of multivesicular hydatid cysts. J Comp Assist Tomogr 1986; 10: 428-431. 11 Ramos L, Hernandez-More M, Thanas M, Leorient MT, Marcos J. Radiological characteristics of perforated pulmonary hydatid cysts. Radiology 1975; 116: 539-542. 12 McCorkell S. Unintended percutaneous aspiration of pulmonary echinococcal cysts. AJR 1984; 143: 123-126. 13 Pandolfo I, Scribano I, Lavagnini L, Termini S, Longo M. Clinical images. Post-traumatic intraperitoneal dispersion of echinococcal disease. J Comput Assist Tomogr 1982; 6: 1034-1035. 14 Ptasnik R, Hennessy FO. Pelvic hydatid disease as acute urinary retention. BJR 1988; 61: 146-165. 15 Selli C, Seghi P, Pralesi C, Carini M. Retrovesical echinococcal
cyst causing acute urinary retention. Urology 1983; 22: 284-285. 16 Stampfel G. Anaphylactoid reaction: a rare complication after fine needle biopsy of the lungs. Radiology 1982; 22: 329-336. 17 Mueller P, Dawson SL, Ferrucci JT, Mardi GL. Hepatic echinococcal cyst: successml drainage. Radiology 1985; 155: 627-628. 18 Bret PM, Fond A, Bretagnolle M, Valette PJ, Thiese P, Lambert R, Labodie M. Percutaneous aspiration and drainage of hydatid cysts in the liver. Radiology 1988; 168: 617-620. 19 Chemtai AK, Bowny TR, Ahmad Z. Evaluation of five immunodiagnostic techniques in echinococcosus patients. Bull. WHO 1981; 59: 767-772. 20 Morris DL, Skene-Smith H, Haynes A, Burrows FGO. Abdominal hydatid disease: computed tomographic and ultrasound changes during albendazole therapy. Clin Radio1 1984; 35: 297-300. 21 Bezzi M, Teggi A, De Rosa F, Capozzi A, Tucci G, Bonitiecino A, Angelica L. Abdominal hydatid disease: ultrasound findings during medical treatment. Radiology 1987; 162: 91-95. 22 Esfahani F, Rooholamini SA, Vessal K. Ultrasonography of hepatic hydatid cysts: new diagnostic signs. J Ultrasound Med 1988; 7: 443-458.
31-37
Elsevier
31
EURRAD
00062
Ultrasound, CT and MRI of ruptured and disseminated hydatid cysts W.N. von Sinner Department of Radiology, King Faisal Specialist Hospital, and Research Centre. Riyadh, Saudi Arabia
(Received 22 November
1989; accepted
after revision 28 March 1990)
Key words: Hydatid disease, CT; Hydatid disease, MRI; Hydatid disease, ultrasound
study; Radiography,
hydatid disease
Abstract
Three cases of echinococcus granulosus with rupture of hydatid cysts and widespread abdominal, pelvic or pleural dissemination are described. Ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) allowed recognition of ruptured hydatid cysts. This assisted to come to an appropriate therapy and exclusion or confirmation of hydatid cysts elsewhere in the body. Ultrasound, CT and MRI are also important for follow-up, evaluation of therapeutic response and/or early diagnosis of recurrence.
Introduction Echinococcus granulosus is endemic in many sheepand cattle-raising countries throughout the world. Delayed diagnosis is common, and often results in spreading of the disease. Unrecognized hydatid cysts may become very big and rupture. Anaphylactic reactions include life-threatening shock. Abdominal, pelvic and pleural dissemination due to discharge of parasitic contents may follow, causing growth of innumerable daughter cysts excluding curative surgery. Modem imaging modalities, such as ultrasound, computed tomography and magnetic resonance imaging are helpful in diagnosing the disease and making effective therapy possible. I have observed a number of ruptured hydatid cysts with dissemination and would like to publish the experience with these cases. Material and Methods The cases of hydatid disease with abdominal, pelvic and/or pleural dissemination secondary to rupture of hepatic or splenic hydatid cysts are described. Address for reprints: Dr. W.N. von Sinner, Department of Radiology, King Faisal Specialist Hospital, P.O. Box 3354, Riyadh 11211, Saudi Arabia. 0720-048X/90/$03.50
0 1990 Elsevier Science Publishers
Ultrasound, CT and MRI were used in all cases, allowing correlations with these imaging modalities. Ultrasound examinations were obtained with an SDR 1500 sector scanner (Picker) and Acuson scanner. CT scans with and without contrast enhancement were obtained using a Somatom DR3 (Siemens), and MR imaging was performed with a 1.5 Tesla machine (Picker) using Tl and T2 conventional spin echo techniques with the following parameters, TR = 850 ms, TE = 20 ms, TR = 2000 ms and TE = 100 ms. The examinations were performed in transaxial, coronal and sag&al planes. Case reports Case 1 A lPyear-old male was referred to our hospital with abdominal pain. The physical exam showed multiple ‘tumors’ in the liver, spleen and abdomen. Ultrasound showed complex cystic changes with a double-line sign suggestive of collapsed parasitic membranes (Fig. la). CT documented widespread involvement of spaceoccupying lesions throughout the abdomen (Fig. lb) and pelvis (Fig. lc) including the peritoneal and retroperitoneal spaces. The indirect hemagglutination (IHA) test was highly positive (1 : 4048). Laparotomy confumed the presence of a large number of hydatid cysts of which many were removed during surgery. Pathology confirmed the presence of scolices. High-dose meben-
B.V. (Biomedical
Division)
32
Fig. 1. Case 1: a 19-year-old male with multiple abdominal and pelvic hydatid cysts. (a) Abdominal ultrasound: complex hepatic cystic changes with double-line structures representing collapsed parasitic membranes (arrows). (b) CT (without contrast enhance-
ment): multiple abdominal hydatid cysts. (c) CT of pelvis (without contrast enhancement): large number of pelvic hydatid cysts. (d) Tl weighted MR image, coronal view, right side, (TR 850 ms, TE 20 ms): ruptured hydatid cyst with peritoneal spillage (black curved arrows). Observe also prolapsed hydatid cyst into right lung base from right liver lobe (straight black arrows). (e) T2 weighted MR image axial view, right side (TR 2000 ms, TE 100 ms): ruptured hydatid cyst with discharge of cystic contents and peritoneal spillage (large straight black arrows). Observe also low intensity rim (small black arrows) and pericystic reaction with edema (curved open arrows).
33
dazole treatment for several months was only partially effective. Most cysts persisted or had increased in size, especially those in the liver and spleen. One liver cyst had ruptured spontaneously, and showed disrupture of the cyst w’all and a low intensity rim with discharge of cystic contents into the peritoneum (Fig. 1 d and e). High-dose albendazole was started. Two months later spectacular regression of most cysts was noted with remarkable improvement in the patient’s condition. Case 2 A lo-year-old male was admitted to our institution who was known to have hydatid disease of the liver. Four years ago, he was re-admitted for recurrent hydatid cysts of the liver. The IHA test was 1 : 2026 (normal 1 : 32). He was re-admitted for a third time 2 years ago. An exploratory laparotomy was performed with the removal and in situ therapy of multiple hydatid cysts after mebendazole treatment had been unsatisfactory. Ultrasound and CT of the abdomen showed multiple hydatid cysts of the liver, the spleen (Fig. 2) and pelvis. The pelvis contained two large cysts, one above the bladder and one deep in the right pelvic fossa associated with a cluster of smaller hydatid cysts in the same area measuring approximately 2-3 cm in diameter each. In addition, many small cysts unattached to organs were found in the retroperitoneum and omentum. Pathology confirmed the presence of hydatid cysts of the liver, spleen and pelvis containing parasitic membranes and scolices.
Fig. 2. Case 2: a IO-year-old male with hydatid disease. CT of abdomen (with barium contrast in stomach) showing hydatid cyst of liver and spleen (with small calcification of the wall) in close relationship to the stomach (arrows).
Case 3 A 40-year-old male presented with abdominal-space occupying lesions known to be caused by multiple hydatid cysts. His history began 5 years ago when he noticed a swelling in his upper abdomen. Two years later he was involved in a traffic accident and his swellings suddenly disappeared. One year after the accident he again noticed abdominal distension. At surgery, hundreds of small hydatid cysts were removed from the abdomen. Pathology confirmed hydatid disease. Mebendazole treatment was carried out for 3 years, with unsatisfactory results. 4 months ago, the patient presented again with new swellings in the abdomen. In his past history there was an episode with jaundice and abdominal pain. The physical examination revealed a large smooth non-tender mass in the right hypochondrium about 8 x 8 cm in size, and also a smaller mass in the left hypochondrium. A third mass in the right lumbar region was not mobile. A non-enhanced and contrast-enhanced dynamic CT showed further increase of some cysts with imminent rupture (Fig. 3a). Three weeks later ultrasound and MRI showed detachment of parasitic membranes, demonstrating the ‘serpent or snake sign’ which is pathognomonic for hydatid cysts (Fig. 3b, c and d). Following surgery he made a good recovery. Discussion After the eggs of Echinococcus granulosus are freed from their coating by digestive enzymes, larvae penetrate the mucosa of the jejunum, reaching venules and lymphatics ; they are carried through the portal circulation into the liver where 50-70x are filtered out. Another 30-40% reach the capillary filter of the lungs, via the inferior vena cava, and only lo-20% arrive in the systemic circulation from which they may be distributed to all organs and tissues of the body. Many larvae die during the passage or when they get stuck in the filters resulting from the host’s defence mechanisms. Those who survive transform into cysts. Their wall differentiates into two layers, the so-called ectocyst consisting of a hyaline membrane, supporting the endocyst (germinal layer) which generates scolices, brood capsules and daughter cysts; they may be pinched off into the central fluid containing area and fall to the bottom of the cyst as ‘hydatidsand’. The host reacts with the formation of an adventitial layer (pericyst) segregating the body from the parasite, consisting of fibroblasts and blood vessels through which the parasite receives nutrients. After 6 months the hydatid cyst reaches a diameter of 1 cm and thereafter grows every year 2-3 cm without
Fig. 3. Case 3: a 40-year-old male with multiple hydatid cysts of the abdomen. (a) CT of abdomen, right side: without contrast enhancement. Large hepatic cyst showing defective posterior cyst wall (white arrows) with low intensity rim (black arrows). (b) Ultrasound of abdomen, right side, showing ‘serpent’ or ‘snake’ sign; cyst wall (black arrow) collapsed parasitic membranes (white arrow). (c) Tl weighted axial MR images, right side, (TR 850 ms, TE 20 ms) demonstrating ‘serpent’ or ‘snake’ sign (arrows). (d) T2 weighted axial MR image, right side, (TR 2000 ms, TE 100 ms) demonstrating ‘serpent’ or ‘snake’ sign (arrows).
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initially causing symptoms. Most patients are infected in their childhood. It takes years for the hydatid cyst to reach a substantial size [l-20]. Vital structures may then be affected and vague symptoms may arise depending on the location of the cyst, the organ affected and the type of vital structures involved. In the asymptomatic period, Echinococcosis may be discovered by conventional radiographs if the cysts are calcified [ 2,3,4]. Uncalcified cysts are usually demonstrated by ultrasound [2,7], CT [3,5,10] or MRI [4-61. In the early stages their appearance may be uncharacteristic. A ‘double line’ is not infrequently found in unruptured hydatid cysts (Fig. la) [22]. If present, hydatid cysts can be differentiated from simple cysts, cystic tumors, metastases, abscesses etc. Serologic tests [ 191 may be helpful in confirming a suspected diagnosis. However, the usual intradermal tests (Casoni) and Weinberg’s complement fixation test have been evaluated by many authors to be unreliable, because of false-positives or false-negatives of the former, and possible negative results of the latter. Moreover, patients with other helminthic diseases, particularly schistosomiasis, may have false-positive results. Modern tests such as the IHA test and latex agglutination test are more reliable; but even these may have false-positive or false-negative results. The presence of ‘arc 5’ in a recently described immunoelectrophoresis is more promising for diagnosis of Echinococcus but its wide use is limited due to technical reasons. With the expansion of the spaceoccupying lesion, a bulge in the liver or spleen may stretch the capsule, causing pressure atrophy and necrosis [ 5,201. This may lead to a small dissection of the pericystic and/or the parasitic layers, bleeding of blood vessels, erosion of bile ducts, and finally to a frank rupture of the capsule and of the parasitic germinal layers (endocyst and/or ectocyst) [ 7,8]. The fluid pressure in the hydatid cysts in quite high, and, as a consequence, the fragile parasitic membranes may split and small dissections may occur through which parasitic fluid may evade into the virtual space between the pericyst and the ectocyst, causing detachment or collapse of the parasitic membranes. If air is entering from the outside through defects in the pericyst, such as may occur if bronchioles, bile ducts or air-containing organs are eroded, air may enter the space between the pericyst and ectocyst leading to detachment of the parasitic membranes, as has been described in pulmonary hydatid cysts (sign of detachment or crescent/meniscus sign; ‘water-lily sign’). Small amounts of parasitic liquid may evade through these small defects and be discharged into the blood vessels or the peritoneum of the patient. If the patient is sensitized against the foreign
proteins of the hydatid fluid, hydatid sand or daughter cysts, anaphylactic reactions or shock [ $12,161 and dissemination may ensue [ 131. The increasing size and age of the cysts, may lead to areas of degeneration of the cystic membranes and production of brood capsules and daughter cysts, and spontaneous detachment of the parasitic membranes. Degeneration by aging or trauma, toxins, chemotherapy or lack of nutrients, may lead to damage of the cystic wall with an increased risk of rupture. Recently, a low intensity rim thought to represent the pericyst has been described surrounding hydatid cysts of the liver (Fig. le) [4]. We have confirmed its existence on T2 weighted MR images, not only in liver cysts but also in hydatid cysts of the thoracic wall the lungs [ 51, where they may be more marked due to the compression of lung parenchyma, atelectatic tissue and secondary allergic reactions against the parasite. If the cyst is surrounded by normal lung parenchyma, this low intensity rim may be difficult to detect. Usually the place where the cyst is abutting on the thoracic wall can be clearly seen. A defect in the pericyst (adventitial layer) may be demonstrated on CT (Fig. 3a) and/or MRI imaging (Fig. le). On MRI [ 5,6,8] recognition is easier on standard Tl and T2 conventional spin-echo techniques in different planes (axial, coronal, sagittal and intermediate planes). Undulated membranes are rarely seen on ordinary radiographs but are pathognomonic for hydatid disease on ultrasound, CT and MRI, having the appearance of a ‘snake’; therefore, I call this pathognomonic sign the ‘serpent’ or ‘snake’ sign (Fig. 3b, c and d). Although the appearance of collapsed membranes on conventional radiographs and ultrasound has previously been described and occasionally been mentioned on CT, to the best of my knowledge, no previous publication has been found identifying it on MRI. There are also differences in the ‘water-lily sign’, described since collapsed membranes are floating on fluid. In our cases the importance of this ‘serpent’ or ‘snake’ sign as a pathognomonic sign allowing confident diagnosis of hydatid disease could be clearly demonstrated (Fig. lc, d and e). It has not been shown to occur in any other disease or disposition. In the actual event that a hydatid cyst ruptures, this may be accompanied by allergic phenomena, such as urticaria, asthma, collapse or even anaphylactic shock [ 161, in addition to abdominal pain pointing to an acute abdominal event. Expanding cysts may show erosion of the cystic wall, suggesting imminent rupture (Fig. 3a). A defective low-intensity rim on MRI, as demonstrated in Case 3, confirms rupture of the cyst. Following rupture, a ‘serpent’ or ‘snake’ sign may be demonstrated on ultrasound, CT and MRI (Fig. 3a, b and c). The actual
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event of cystic discharge as a result of spontaneous silent rupture of the wall of the bulging hydatid cysts can as such also be visualized (Fig. Id and e). Such a discharge of cystic contents may generate abdominal and pelvic daughter cysts by peritoneal seeding (Fig. lb and d) [ 13,151. Albendazole treatment appears to be prophylactically and therapeutically effective. Growing hepatic and splenic cysts may also cause pressure atrophy of the diaphragm with prolapse into the lung parenchyma (if adhesions are present) (Fig. Id) or into the pleura (if there are no adhesions) causing secondary pleural dissemination if rupture occurs [ 5,9,1 I]. Rupture of a hydatid cyst predisposes infection of the cyst. If rupture into the pleural space occurs, pneumothorax, pyopneumothorax or a life-threatening tension pneumothorax [ 81 may follow. The exact frequency with which infection of hydatid cysts or of the neighboring tissues occurs is unknown and a matter of controversy. Some authors [21] regard this as a relatively rare event. Others [ 2,7,8,1 l] have observed it rather unfrequently. Based on my preliminary data, infection of ruptured hydatid cysts appears to be relatively common. In my own experience there are three main mechanisms of infection: (1) infection of the cyst due to damage of the pericyst, leading to abscess formation. The diagnosis in these cases is often missed, since it is usually diagnosed as a pyogeneous abscess; (2) rupture of a hydatid cyst with leakage of hydatid fluid causing allergic reaction of the pericystic tissue accompanied by edema (Fig. le). The damaged tissue may be invaded secondarily by bacteria or other agents, leading to a real secondary inflammation; (3) infection of residual or retained hydatid tissue or membranes. Imaging by ultrasound, CT or MRI, may be helpful in clarifying the situation. The demonstration of air bubbles or gas within the lesion and contrast enhancement (e.g., ring enhancement) on CT are strong indicators of infection and abscess formation. Several reports of successful drainage of hydatid infected cysts have appeared in the literature [ 17,181. If a hydatid cyst ruptures into vascular structures, secondary vascular dissemination may ensue. Some cases have been observed where a splenic hydatid cyst had ruptured into other organs, such as the stomach or the left kidney or the colon (see close relationship with these organs as demonstrated in Fig. 2). If viable material containing a large number of viable larvae is discharged into the stomach secondary infection may occur. Growing secondary cysts in the small pelvis may also lead to compression of the bladder and ureters causing obstruction of the urinary pathways leading to bilateral hydronephrosis [ 14,151. Ultrasound, CT and MRI play a keyrole in
diagnosing and monitoring surgically or chemotherapeutically treated disseminated hydatid disease. They are of great help in excluding or confirming any other hydatid cysts locations in the chest, brain or elsewhere in the body. Recurrence of hydatid cysts can easily be detected by CT and MRI before they have spread to other areas or caused deterioration of the patient’s condition. In chemotherapeutically treated patients (e.g., with albendazole), the progress or the improvement of the hydatid disease can be periodically followed until its total resolution. The significance of this study is based on: (1) A new pathognomonic sign that can be identified on Tl and T2 weighted MR images, called the ‘serpent’ or ‘snake’ sign and which allows the specific diagnosis of hydatid disease. Other signs of hydatid disease, such as ‘low intensity rim’ or ‘daughter cysts’ may be helpful and assist in the diagnosis, but are not pathognomonic ‘per se’. (2) Ultrasound, CT and MRI are useful in recognizing rupture and other complications of hydatid cysts. They may exclude or confirm the presence of other hydatid cysts elsewhere in the body. (3) Recognition of ruptured hydatid cysts by ultrasound, CT and MRI is important for appropriate therapy. (4) In abdominal, pelvic or pleural dissemination, where curative surgery is not possible, albendazole therapy may lead to a significant regression of the hydatid disease, as has been documented by ultrasound, CT and MRI. Acknowledgement I wish to express my appreciation to Miss Catherine Devane for her skilful secretarial assistance. References Beggs L. The radiology of hydatid disease. AJR 1985; 15: 639-648. Lewall DB, McCorkell SJ. Hepatic echinococcus cysts: sonographic appearance and classification. Radiology 1985; 155: 113-715. Haertel CF, Fretz CH, Fuchs WA. Computed tomography in the diagnosis of echinoccosus (in German). ROEFO 1980; 133: 164-170. Hoff, FL, Aisen AM, Walden MR, Glazer GM. MR imaging in hydatid disease ofthe liver. Gastrointest Radio1 1987; 12: 29-42. v. Sinner WN, Rifai A, te Strake L, Sieck J. MR imaging of thoracic hydatid disease; correlation with clinical findings, conventional radiography, ultrasound, CT and pathology. Acta Radio1 (Diagn) 1990, in press. Morris DL, Buckley J, Gregson R, Worthington BS. MR imaging in hydatid disease. Clin Radio1 1987; 38: 141-144.
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7 Lewall DB, McCorkell SJ. Rupture of echinococcal cysts: diagnosis, classification and clinical implications. AJR 1986; 146: 391-394. 8 Lupetin AR, Dash N: Intrahepatic rupture of hydatid cyst: MR findings. AJR 1988; 151: 491-492. 9 Yacoubian HD. Thoracic problems associated with hydatid cyst of the dome of the liver. Surgery 1976; 79: 544-548. 10 Kalovidouris A, Pissiotis C, Pontifex G, Gouliamos A, Penken S, Papavassilion C. CT characterization of multivesicular hydatid cysts. J Comp Assist Tomogr 1986; 10: 428-431. 11 Ramos L, Hernandez-More M, Thanas M, Leorient MT, Marcos J. Radiological characteristics of perforated pulmonary hydatid cysts. Radiology 1975; 116: 539-542. 12 McCorkell S. Unintended percutaneous aspiration of pulmonary echinococcal cysts. AJR 1984; 143: 123-126. 13 Pandolfo I, Scribano I, Lavagnini L, Termini S, Longo M. Clinical images. Post-traumatic intraperitoneal dispersion of echinococcal disease. J Comput Assist Tomogr 1982; 6: 1034-1035. 14 Ptasnik R, Hennessy FO. Pelvic hydatid disease as acute urinary retention. BJR 1988; 61: 146-165. 15 Selli C, Seghi P, Pralesi C, Carini M. Retrovesical echinococcal
cyst causing acute urinary retention. Urology 1983; 22: 284-285. 16 Stampfel G. Anaphylactoid reaction: a rare complication after fine needle biopsy of the lungs. Radiology 1982; 22: 329-336. 17 Mueller P, Dawson SL, Ferrucci JT, Mardi GL. Hepatic echinococcal cyst: successml drainage. Radiology 1985; 155: 627-628. 18 Bret PM, Fond A, Bretagnolle M, Valette PJ, Thiese P, Lambert R, Labodie M. Percutaneous aspiration and drainage of hydatid cysts in the liver. Radiology 1988; 168: 617-620. 19 Chemtai AK, Bowny TR, Ahmad Z. Evaluation of five immunodiagnostic techniques in echinococcosus patients. Bull. WHO 1981; 59: 767-772. 20 Morris DL, Skene-Smith H, Haynes A, Burrows FGO. Abdominal hydatid disease: computed tomographic and ultrasound changes during albendazole therapy. Clin Radio1 1984; 35: 297-300. 21 Bezzi M, Teggi A, De Rosa F, Capozzi A, Tucci G, Bonitiecino A, Angelica L. Abdominal hydatid disease: ultrasound findings during medical treatment. Radiology 1987; 162: 91-95. 22 Esfahani F, Rooholamini SA, Vessal K. Ultrasonography of hepatic hydatid cysts: new diagnostic signs. J Ultrasound Med 1988; 7: 443-458.