British Journal of Radiology 74 (2001),283-289 © 2001 The British Institute of Radiology
The imaging appearances of hydatid disease at some unusual sites
M H Dahniya, FRCR, FWACS
1
R M Hanna, MD, FRCR
1
S Ashebu, MBBS, FWACS
2
S A Muhtaseb, MSc, MD
2
A El-Beltagi, FFR, RCSI
1
S Badr, FFR, RCSI
1 and
E El-Saghir, MSc
1
1 Department of Diagnostic Radiology and Imaging, Al-Sabah Hospital
2 Department of Diagnostic Radiology and Imaging, Al-Adan Hospital, Kuwait
Correspondence: M H Dahniya, PO Box 31162, 90802 Sulaibikhat, Kuwait
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Abstract
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On reviewing our cases of hydatid disease seen over a period of 20 years (1978–1998), we encountered a number of unusual radiological appearances and sites, which are demonstrated in this pictorial review. We briefly discuss the pathology of hydatid disease and its complications.
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Introduction
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Hydatid disease is caused by the cystic stage of infestation by Echinococcus granulosus. The disease is prevalent in most parts of the world, especially in sheep farming and cattle farming areas of Asia, North and East Africa, South America, Australasia and the Middle East [1]. The adult worm lives in the intestine of the definitive host, which includes dogs and other carnivorous animals. Sheep, cattle and humans act as the intermediate host. Man becomes infected through contact with a definitive host or by consuming contaminated water or vegetables [2].
Most hydatid cysts occur in the liver (59–75%), followed in frequency by the lung (27%). Involvement of the kidney (3%), bone (1–4%) and brain (1–2%) is rare. Other sites, such as the heart, spleen, pancreas and voluntary muscle, are very rarely involved, but no site is immune [2].
A pathology-based classification has recently been introduced by Lewall [3]. The initial lesion (Type I cyst) is a fluid-filled cystic structure with three layers: the outermost pericyst composed of modified host cells and fibrous tissue; the middle laminated membrane resembling the white of an egg; and the thin inner germinal membrane. The germinal membrane produces the laminated membrane and the scolices that represent the larval stage [2]. Hydatid cysts enlarge progressively, with the development of many daughter cysts within the cavity of the large parent cyst. The cystic fluid is a transudate of serum that contains proteins and is antigenic. When Type I cysts develop daughter cysts and/or matrix they become Type II cysts. When the nourishing hydatid fluid is replaced by formed elements the lesion dies and eventually becomes calcified and biologically inert, forming a Type III lesion [3]. Complications of hydatid disease include rupture of Type I and II cysts as well as secondary infection. There are three types of rupture [3, 4]. In contained rupture, which is clinically silent, the endocyst ruptures and the cyst contents are confined within the pericyst. In communicating rupture, the cyst ruptures into the biliary and bronchial radicles that are incorporated in the pericyst and may result in biliary obstruction or secondary infection. Direct rupture implies rupture of both the endocyst and the pericyst, with spill of cyst contents into the peritoneal or pleural cavities or other structures. Rupture into a hollow viscus, such as stomach or colon, is exceedingly rare [5, 6].
Direct rupture has the greatest clinical consequences, including anaphylaxis, hydatid dissemination and secondary bacterial infection [3]. Most hydatid cysts are asymptomatic and are diagnosed incidentally. Both ultrasound and CT are sensitive in detecting hydatid cysts. Plain radiographs are useful in certain circumstances, for example imaging pulmonary and bone lesions as well as calcification in soft tissues [3]. Ultrasound and/or CT are important in evaluation of Type I and II lesions in solid organs. Cerebral hydatids can be imaged by either CT or MRI, but MRI is particularly useful because of its multiplanar capabilities and more detailed anatomical resolution [3].
The plain radiographs, ultrasound images and CT scans of 357 cases of hydatid disease seen over a period of 20 years (1978–1998) were reviewed. 234 patients were males and 123 were females. Their ages ranged from 8–79 years (mean 51 years). Cases in unusual sites and with unusual appearances were selected for this review. Pathological confirmation was obtained after surgery in all cases illustrated, except the cardiac hydatid.
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Chest
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The lung was the second most commonly involved organ in our series. In two cases, the cysts were confined to the anterior mediastinum, which is an uncommon site. In one of these cases, two large Type I cysts of virtually equal size were adjacent to each other, resulting in a bilobed appearance (Figure 1
). Cardiac hydatid, which is also rare [3], was encountered only once, in an asymptomatic patient (Figure 2).
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Figure 1. (a) 27-year-old male with chest pain and dyspnoea. Chest radiograph shows well defined bilateral perihilar masses. The lung fields are clear. (b) Contrast enhanced CT at the level of the ascending aorta shows two adjacent large Type I hydatid cysts in the anterior mediastinum.
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Figure 2. Posteroanterior and left oblique chest radiograph showing a calcified (Type III) hydatid cyst in the wall of the left ventricle in an asymptomatic 38-year-old male.
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Abdomen
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The liver was the most commonly involved organ in our series. One patient showed a bilobed appearance of the cyst (Figure 3). There were several instances of communicating rupture of liver cysts, with atypical appearances in a few (Figure 4). Multiple cysts, usually of varying sizes, were common. Involvement of the spleen is uncommon, representing less than 2% of all human infestations [7]. Isolated splenic involvement is even more uncommon. We encountered three such cases: one had a typical Type I cystic appearance (Figure 5); the second was a Type II cyst (Figure 6); and the third, a Type II/III cyst, ruptured into the peritoneal cavity and the disseminated daughter cysts later calcified (Figure 7). An isolated cyst was seen in the lesser sac in two patients, both of whom presented with epigastric pain and a palpable mass. The cyst was calcified in one patient (Figure 8). Primary hydatid disease of the pancreas is rare, the reported incidence being 0.25% [8]. The only case in our series was a 35-year-old male with recurrent upper abdominal pain. Ultrasound and CT showed a cystic lesion in the body and tail of the pancreas, the CT appearances being typical of hydatid disease. Laparotomy confirmed hydatid disease (Figure 9). Isolated retroperitoneal cysts were rare in our series. In one case, a very large cyst caused marked displacement of the left kidney (Figure 10). A solitary retroperitoneal cyst presenting as a thigh mass has been reported [9]. One of our patients, who was being investigated for infertility, had a Type III cyst in the right seminal vesicle (Figure 11). As far as we are aware, isolated hydatid in a seminal vesicle has not been reported previously.
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Figure 3. Contrast enhanced CT of the abdomen at the level of the left kidney. Two large hydatid cysts of equal size in the right lobe of the liver in a 40-year-old male.
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Figure 4. Contrast enhanced CT of the upper abdomen in a 19-year-old patient, showing a stage II hypermature cyst, with loss of peripheral definition and interior clarity, and daughter cysts filling the centre. There is evidence of communicating rupture, with biliary dilatation "upstream" (arrow). Small amount of ascites is present (arrowhead).
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Figure 5. Contrast enhanced CT of the upper abdomen in a young patient with abdominal discomfort and progressive abdominal distension. A giant isolated Type I splenic cyst displaces bowel to the right.
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Figure 6. Non-enhanced CT of the upper abdomen showing an isolated Type II hypermature cyst in the spleen, with daughter cysts (arrowhead) and matrix with a density of 34 HU (arrow).
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Figure 7. Plain abdominal radiograph in a 45-year-old physician with an isolated Type II/III cyst in the spleen. He presented with an acute abdomen and anaphylactic shock due to direct rupture of the cyst into the peritoneal cavity. A large number of daughter cysts were removed at laparotomy. 3 years later, an abdominal radiograph shows extensive calcification of the residual disseminated daughter cysts.
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Figure 8. Contrast enhanced CT of the upper abdomen, showing a solitary calcified hydatid cyst in the lesser sac. The patient presented with abdominal pain and a palpable epigastric mass.
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Figure 9. Contrast enhanced CT of the abdomen, showing hydatid disease involving the body and tail of the pancreas (arrow) in a 35-year-old male. Note daughter cysts (arrowhead).
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Figure 10. Non-enhanced CT of the abdomen in a 29-year-old patient, showing a large Type II solitary retroperitoneal hydatid cyst displacing bowel anteriorly. The left kidney was displaced inferiorly and malrotated.
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Figure 11. (a) Plain abdominal radiograph of a 38-year-old patient with infertility and ejaculatory difficulty, showing a calcified lesion in the right side of the pelvis. (b) CT shows the calcified lesion to be in the region of the right seminal vesicle. The lesion was removed and pathological examination confirmed hydatid disease of the seminal vesicle.
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Musculoskeletal system
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Hydatid disease of bone is rare, although its incidence in Kuwait (4%) is higher than in Australia (1.1%) and Spain (2.5%) [10–13]. A lucent expansile lesion with cortical thinning is the most common radiological pattern, and pathological fractures are common [2, 13]. In descending order, the vertebrae, long bone epiphyses, pelvis, skull and ribs are most frequently affected [2]. Soft tissue involvement with calcification is highly suggestive of the disease [13]. We encountered five cases of osseous hydatid disease, one each in a rib (Figure 12), humerus and fibula, and two in a femur (Figure 13). Associated soft tissue calcification was not seen. Soft tissue hydatid disease is rare even in endemic areas, and a primary focus within muscle in the absence of pulmonary or hepatic involvement is most unusual [14]. We encountered only two cases of primary intramuscular hydatid disease in our series, one in the shoulder and the other in the thigh. Ultrasound showed multiple cystic lesions in the muscles. CT showed similar cystic appearances, with faint peripheral contrast enhancement of the cysts (Figures 14 and 15). The MRI appearances of primary intramuscular hydatid disease have been reported [15].
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Figure 12. (a) An expanding cystic lesion in the left sixth rib of a 31-year-old patient with chest pain and left-sided chest swelling. (b) CT showed an expanding lesion with a dense matrix of 61 HU. The rib was resected and hydatid disease was confirmed.
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Figure 13. Plain radiograph of the right femur in a 60-year-old man, showing extensive osteolytic destruction with cortical thinning, pathological fractures and soft tissue extension. Metastatic disease or myeloma was the initial diagnosis. Hydatid disease was confirmed at surgery.
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Figure 14. Contrast enhanced axial CT of the left shoulder in a 32-year-old male with a painless swelling for 2 years, showing multiple cysts with peripheral enhancement.
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Figure 15. Contrast enhanced axial CT of a 23-year-old male with painless swelling of the right thigh. Multiple hydatid cysts with daughter cysts producing a multiloculated appearance in the rectus femoris and vastus lateralis muscles.
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Hydatid disease may occur anywhere [2], from the big toe [16] to the crown of the head [17]. In endemic areas, a high index of suspicion is required for correct diagnosis when it presents in an unusual site or with an atypical radiological appearance.
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Acknowledgments
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We are grateful to Mrs Viyena Rodrigues for her secretarial assistance.
Received for publication December 16, 1999.
Revision received April 25, 2000.
Accepted for publication June 9, 2000.
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Top
Abstract
Introduction
