DOI: 10.1148/rg.232025704
(Radiographics. 2003;23:475-494.)
© RSNA, 2003
Hydatid Disease from Head to Toe1
Pinar Polat, MD,
Mecit Kantarci, MD,
Fatih Alper, MD,
Selami Suma, MD,
Melike Bedel Koruyucu, MD and
Adnan Okur, MD
1 From the Department of Radiology, Faculty of Medicine, Atatürk University, Erzurum, Turkey. Received April 15, 2002; revision requested June 11 and received August 16; accepted August 19. Address correspondence to P.P., Istasyon mah, Kombina cad, Armagan Apt 4/7, Erzurum, Turkey (e-mail: drppolat@hotmail.com).
 |
Abstract
|
|---|
Hydatid disease (HD) is a unique parasitic disease that is endemic in many parts of the world. HD can occur almost anywhere in the body and demonstrates a variety of imaging features that vary according to growth stage, associated complications, and affected tissue. Radiologic findings range from purely cystic lesions to a completely solid appearance. Calcification is more common in HD of the liver, spleen, and kidney. HD can become quite large in compressible organs. Hydatid cysts (HCs) can be solitary or multiple. Chest radiography, ultrasonography (US), computed tomography (CT), magnetic resonance (MR) imaging, and even urography can depict HCs. The imaging method used depends on the involved organ and the growth stage of the cyst. US most clearly demonstrates the hydatid sands in purely cystic lesions, as well as floating membranes, daughter cysts, and vesicles. CT is best for detecting calcification and revealing the internal cystic structure posterior to calcification. MR imaging is especially helpful in detecting HCs of the central nervous system. Radiologic and serologic findings can generally help establish the diagnosis of HD, but an HC in an unusual location with atypical imaging findings may complicate the differential diagnosis. Nevertheless, familiarity with imaging findings, especially in patients living in endemic regions, is advantageous in this context.
© RSNA, 2003
Index Terms: Brain, parasites, 10.208 • Computed tomography (CT), utilization, **.12112 • Echinococcosis, 60.2083, 10.208, 76.2083 • Liver, echinococcosis, 76.2083 • Magnetic resonance (MR), utilization, **.1214 • Parasites, 60.2083, 10.208, 76.2083 • Ultrasound (US), utilization, **.1298
|
LEARNING OBJECTIVES FOR TEST 6
|
|---|
After reading this article and taking the test, the reader will be able to:
- Describe the imaging features of hydatid disease in various anatomic locations.
- Discuss the roles of US, CT, and MR imaging in the diagnosis of hydatid disease.
|
Introduction
|
|---|
There are two types of Echinococcus infections. E granulosis is the more common type, whereas E multilocularis is less common but more invasive, mimicking a malignancy. Hydatid disease (HD) continues to be a significant health problem in underdeveloped areas where animal husbandry is common but no veterinary control exists (eg, parts of South America, the Mediterranean region, the Middle East, Africa, and Australia). In Europe, HD is uncommon and is seen only in immigrants or persons with a history of travel to endemic areas (1–8).
HD is endemic in the eastern part of Turkey, and our university hospital is a referral hospital in this region. We studied a group of 368 patients in whom HD was diagnosed and who were treated at our hospital between 1996 and 2001. In this article, we describe the results of our study in terms of (a) radiologic findings, (b) sites of involvement, and (c) systemic involvement in the abdomen, thorax, head and neck, and soft tissue and bone.
|
Overview of HD
|
|---|
Dogs or other carnivores are definitive hosts, whereas sheep or other ruminants are intermediate hosts. Humans are secondarily infected by the ingestion of food or water that has been contaminated by dog feces containing the eggs of the parasite. After the outer capsule of the egg has been ingested, the freed embryo (oncosphere) enters a branch of the portal vein by passing through the duodenal mucosa. Most of these embryos become lodged in the hepatic capillaries, where they either die or to grow into hydatid cysts (HCs). Some pass through the capillary sieve and become lodged in the lungs and other organs (1,2).
An HC has three layers. The outer layer, or pericyst, consists of modified host cells, fibroblasts, giant cells, and eosinophils, which together form a rigid protective layer only a few millimeters thick. The pericyst represents the response of the host to the parasite. The middle laminated membrane resembles the white (albumen) of a hard-boiled egg and is easily ruptured. This membrane is acellular and is about 2 mm thick. It permits the passage of nutrients but is impervious to bacteria. Disruption of the laminated membrane predisposes to infection. The inner germinal (or germinative) layer is thin and translucent. Scolices, the infectious embryonic tapeworms, develop from an outpouching of the germinal layer known as the brood capsule. Freed scolices together with brood capsules form hydatid sand, which settles in the dependent part of the cyst.
The thickness of these layers depends on the tissue in which the cyst is located. The layers tend to be thick in the liver, less developed in muscle, absent in bone, and sometimes visible in the brain.
The cyst fluid is crystal clear. It is a transudate of serum, contains proteins, and is antigenic. If it is released into the circulation of the host, it can cause eosinophilia or anaphylaxis, although cyst rupture may be clinically silent (1).
|
Radiologic Findings
|
|---|
HCs are classified into four types on the basis of their appearance (2).
Type I: Simple Cyst with No Internal Architecture
Type I HCs appear as a well-defined anechoic mass with or without hydatid sand and septa. Unilocular cysts are considered to be an initial stage in the development of the parasite (Fig 1). Rolling the patient during evaluation disperses the sand, creating small echogenic foci, or "falling snowflakes." At CT, a type I HC appears as a well-defined, water-attenuation mass. Frequently, the septa and cyst wall enhance after injection of contrast material at CT and magnetic resonance (MR) imaging, a finding that helps differentiate type I HC from a simple liver cyst. MR imaging features are also similar to those of a simple liver cyst and include hypointensity on T1-weighted images and marked hyperintensity on T2-weighted images. A low-signal-intensity rim ("rim sign"), which is more evident on T2-weighted MR images, has been described as characteristic of hydatidosis as opposed to nonparasitic cysts in the liver and lungs. This finding represents the parasitic membranes and pericyst. However, it is a nonspecific finding that can also be seen in amebic abscess, hepatocellular carcinoma, and hematoma.
View larger version (105K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1. Incidentally found type I HCs in a 45-year-old woman. Computed tomographic (CT) scan shows multiple unilocular hypoattenuating lesions in the liver (maximum lesion diameter, 15 mm) and spleen (maximum lesion diameter, 30 mm) and one lesion in the tail of the pancreas. The presence of multiple hypoattenuating lesions suggests polycystic liver disease. Casoni and Weinberg test results were positive, and fine-needle aspiration biopsy revealed HD.
|
|
Type II: Cyst with Daughter Cyst(s) and Matrix
Daughter cysts are seen inside the mother cyst. Floating membranes or vesicles can also be seen in the cyst (Fig 2). Sometimes multiple cysts and echogenic areas that are enclosed together within a single capsule give rise to a "racemose" or "wheel spoke" appearance. Consolidation of the daughter cysts may produce echogenic solid lesions.
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2. Detachment of the endocyst from the pericyst in a type II hepatic cyst. Contrast material-enhanced CT scan demonstrates a large, unenhanced cystic lesion with internal floating membranes that occupies almost the entire left hepatic lobe.
|
|
At CT, type II HCs can be visualized in three stages depending on the age, number, and arrangement of the daughter cysts (3). Type IIA lesions contain round daughter cysts arranged at the periphery (Fig 3). The average CT attenuation of the mother cyst is higher than that of daughter cysts. Type IIB lesions contain larger, irregularly shaped daughter cysts that occupy almost the entire volume of the mother cyst. The high-attenuation fluid that surrounds the daughter cysts within the mother cyst looks like septa, creating a "rosette" appearance (Fig 4). Type IIC lesions appear at CT as relatively high-attenuation round or oval masses with scattered calcifications and occasional daughter cysts. These findings represent the degeneration of old cyst with amorphous and tenacious content.
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3. Type IIA hepatic cyst with peripheral calcification. CT scan shows an unenhanced hypoattenuating mass with well-defined borders in the subdiaphragmatic portion of the liver. Multiple round daughter cysts are seen peripherally within the lesion. Note also the peripheral curvilinear wall calcification, which is best seen at CT.
|
|
View larger version (102K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4. Type IIB hepatic cyst. CT scan demonstrates a large, unenhanced hypoattenuating mass with irregularly shaped daughter cysts that occupies most of the left hepatic lobe. Note that the daughter cysts occupy almost the entire volume of the mother cyst (rosette sign).
|
|
At MR imaging, daughter cysts may appear hypointense or isointense relative to the maternal matrix on T1- and T2-weighted images. The "serpent sign," or "snake sign," which represents collapsed parasitic membranes secondary to damage or degeneration of an HC, is another MR imaging manifestation of an HC. These membranes have low signal intensity with all sequences.
Type III: Calcified Cyst
Type III lesions are dead cysts with total calcification. They demonstrate strong posterior shadowing at ultrasonography (US) and manifest as round, hyperattenuating areas at CT and hypointense areas at MR imaging.
Type IV: Complicated HC
HC complications include rupture and superinfection and may be seen in both type I and type II HCs. Rupture occurs in 50%–90% of cases. Cyst rupture is mainly due to the degeneration of parasitic membranes as a result of age, chemical reactions, or a host defense mechanism (Fig 5) (8). HC rupture may be contained, communicating, or direct. In contained rupture, undulating membrane resulting from separation of the endocyst from the pericyst is seen at both US and CT and manifests as postural changes. A "snowstorm" pattern has been described at US. The infected HC may exhibit mixed echogenicity. At T2-weighted MR imaging, the membranes appear as hypointense linear regions. Communicating rupture appears more echogenic than contained rupture at US. Layering of hydatid sand can be seen in the biliary channels in cases of intrabiliary rupture. Fissures in the cyst wall can be visualized at both CT and MR imaging. Cysts may also rupture directly into pleural and peritoneal cavities. Bacterial superinfection of HC is always secondary to rupture. Up to 25% of ruptured cysts may become infected. Numerous signs of cyst infection have been described, including poor delimitation, mixed internal echoes, and air-fluid or fluid-fluid levels. However, these signs can also be seen in both intact HC and ruptured, uninfected HC. The presence of air within the cyst establishes the diagnosis of direct or communicating rupture but does not necessarily imply infection (8).
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5. Rupture of a type IV hepatic cyst into the biliary tree in a 48-year-old man who presented with acute onset of jaundice and pain in the right upper quadrant. CT scan reveals a nonenhancing mass with irregular contours that occupies a small portion of the right hepatic lobe and caudate lobe. Isoattenuating detached membranes appear as serpentine structures within the lesion and protrude into the common bile duct.
|
|
|
Sites of Involvement
|
|---|
The liver was the most frequent site of involvement in our study (74.8% of cases). Of the 275 patients with liver involvement, 133 (48.3%) had isolated liver involvement, 74 (26.9%) had concomitant liver and lung involvement, and 68 (24.7%) had concomitant involvement of the liver and of organs other than the lung (Table).
The second most common site of involvement in our series was the lung (n = 89 [24%]). Seventy-four of these 89 cases (83.1%) demonstrated isolated lung involvement. Other sites of involvement (in decreasing order of frequency) included the peritoneum, kidney, brain, mediastinum, heart, bone, soft tissues, spinal cord, spleen, pleura, adrenal glands, bladder, ovary, scrotum, and thyroid gland (Table). Ovarian and thyroid gland involvement in our study were not systemic, whereas bladder and scrotum involvement were concomitant with liver and peritoneal disease.
|
Systemic Involvement
|
|---|
Abdomen
Liver.—
The liver is the most common site of HD involvement. Most cysts are located in the right lobe. As mentioned earlier, imaging findings in hepatic HD depend on the stage of cyst growth, and the HC can be solitary or multiple. A solitary type I HC may be difficult to distinguish from a simple epithelial cyst on the basis of imaging findings alone. The presence of multiple echogenic foci that fall into the dependent portion of the cyst when the patient is repositioned is a characteristic US finding in HC. Simple epithelial cysts do not demonstrate internal areas of increased echogenicity. When there are multiple unilocular cysts and other organs are involved (eg, pancreas, spleen), polycystic liver or kidney disease is a possible diagnosis (Fig 1). The differential diagnosis can be made when hereditary factors and a history of living in endemic regions are taken into consideration along with these imaging findings. Multiple HCs may be in different stages. Detachment of the endocyst from the pericyst is probably related to decreasing intracystic pressure, degeneration, host response, trauma, or response to therapy. The cyst may appear as a well-defined fluid collection with a localized split in the wall and floating membranes inside the cavity (Fig 2). Multivesicular HCs (type II) may manifest as well-defined fluid collections in a honeycomb pattern, with multiple septa representing the walls of the daughter cysts (Fig 4). Cyst calcification usually occurs in the wall of the HC and is seen at radiography in 20%–30% of liver HCs. Calcification is usually curvilinear or ringlike and involves the pericyst (Figs 3, 6). During the natural course of an HC, complete calcification occurs. Dense calcification may be assumed to indicate the death of the cyst. CT and conventional radiography are the best modalities for detecting calcification.
Perforation to the biliary tree has been described in up to 90% of HCs (8). Rupture may occur through small fissures or bile duct–HC fistulas (55% of cases) or through a wide perforation that allows the access of hydatid membranes to the main biliary ducts (Fig 5).
Involvement of the diaphragm and thoracic cavity occurs in 0.6%–16% of cases of hepatic HD (Fig 7) (4). Transdiaphragmatic migration of HD from the posterior segments of the right hepatic lobe has been reported to be a common complication and is probably related to their proximity to the diaphragm. Intrathoracic rupture of HCs situated in the hepatic dome is a serious complication that results in damage to the pleura, pulmonary parenchyma, and bronchi (4).
View larger version (165K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7a. HD of the liver with involvement of the diaphragm and thoracic cavity in a 54-year-old man. The patient lived in an endemic region and had previously undergone surgery for hepatic HD. (a) Axial contrast-enhanced CT scan through the dome of the liver shows a hypoattenuating lesion that originates from the posterior segment of the right hepatic lobe and has grown through the diaphragm to the lung. (b) Corresponding axial T2-weighted MR image shows the lesion with a multivesicular appearance, transdiaphragmatic growth, and protrusion into the right lower basal lung segment.
|
|
View larger version (121K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7b. HD of the liver with involvement of the diaphragm and thoracic cavity in a 54-year-old man. The patient lived in an endemic region and had previously undergone surgery for hepatic HD. (a) Axial contrast-enhanced CT scan through the dome of the liver shows a hypoattenuating lesion that originates from the posterior segment of the right hepatic lobe and has grown through the diaphragm to the lung. (b) Corresponding axial T2-weighted MR image shows the lesion with a multivesicular appearance, transdiaphragmatic growth, and protrusion into the right lower basal lung segment.
|
|
Spleen.—
The involvement of the spleen in HD is rare. The reported prevalence of splenic involvement varies from 0.9% to 8%. Splenic HC generally develops by means of systemic dissemination or intraperitoneal spread from a ruptured liver cyst. Isolated splenic involvement is very uncommon (5). Splenic HCs are usually solitary, and their imaging characteristics are similar to those of hepatic HCs. Any type of HC can be seen in the spleen (Figs 1, 8). Calcification of the cyst wall may also be seen.
View larger version (51K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8. Type II HC with primary splenic involvement in a 23-year-old woman who lived in an endemic region. The patient had no other organ involvement. Axial contrast-enhanced CT scans through the upper (left) and lower (right) pole of the spleen show a huge, unenhanced low-attenuation mass that occupies almost the entire spleen. Note the peripheral daughter cyst in the superior portion of the mother cyst.
|
|
Pancreas.—
Primary HC of the pancreas is rare, with a reported prevalence of 0.25% (6). The only case in our series involved a 40-year-old woman with multiorgan HC involvement. In this case, there were multiple unilocular cysts in the liver, spleen, and pancreas that simulated polycystic liver disease (Fig 1). The HC was located in the tail of the pancreas and was evaluated as a type I cyst. Information about the appearances and location of HCs within the pancreas is inadequate due to their relatively rare occurrence.
Kidney.—
Involvement of the kidney is rare (3% of cases). Renal HCs are usually located in the upper or lower pole. HCs are frequently solitary and located in the cortex, and they may reach 10 cm in diameter before any clinical symptoms are noted (7). At excretory urography, uncomplicated HCs may create a bulge in the outline of the kidney and appear as a rounded mass that elongates the infindibula and calices. Complications of renal HCs include infection and rupture, in either the renal sinus or the perinephritic tissues. Eighteen percent of renal HCs can rupture into the collecting system, leading to acute colic and hydatiduria (9). In such cases, multiple round filling defects representing daughter cysts can be seen in the excretory system. Any type of HC can be seen in renal HD. Ringlike calcification can be seen in the wall of the HC (Fig 9) (8). Differentiation between a unilocular type I HC and a simple renal cyst may be difficult. A unilocular HC can mimic necrotic renal cell carcinoma, and the presence of calcification does not help distinguish HC from renal cell carcinoma due to the concomitant presence of calcification in the latter. Multilocular HCs can be misdiagnosed as simple renal cysts, cystic nephroma, and cystic variants of renal cell carcinoma. Infected HCs can be misdiagnosed as renal abscess. In short, the differential diagnosis can be made only with percutaneous puncture in most cases (10).
View larger version (116K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9. Primary renal HD in a 26-year-old man who presented with flank pain and signs of a gradually increasing mass in the left upper abdomen. Axial unenhanced CT scan through the middle pole of the kidneys shows a hypoattenuating mass with peripheral daughter cysts and calcification (type II HC).
|
|
Adrenal Gland.—
HD involvement of the adrenal gland is extremely rare. To our knowledge, there have been no reported cases of such involvement in the English medical literature. Unilocular HCs may mimic exophytic renal cysts that originate from the upper pole of the kidney. In our series, there were two cases of unilocular HC that involved the adrenal gland. One HC had the US and CT appearance of a unilocular cyst and was misdiagnosed as an exophytic simple renal cyst. After it became larger and symptomatic during follow-up, surgery was performed and led to the correct diagnosis. The other HC, located in the left adrenal gland, was seen in a 50-year-old man. The diagnosis in this patient was relatively easy due to the presence of multiple serpentine structures with mixed echogenicity that represented collapsed membranes (Fig 10). In both patients, the HC was primary in origin. We did not detect any other foci in either patient.
View larger version (173K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10. Primary HD of the adrenal gland in a 50-year-old man. US image shows a round lesion with mixed echogenicity. Note the serpentine structures within the matrix, a finding that represents collapsed membranes. The diagnosis was made on the basis of US and laboratory findings and was confirmed at surgery.
|
|
Peritoneum and Retroperitoneum.—
Although a few unusual cases of primary peritoneal involvement have been described, peritoneal HCs are almost always secondary to hepatic involvement (11). The overall prevalence of peritoneal involvement in cases of abdominal HD is approximately 13%. Most of these cases are related to previous surgery for hepatic HC, although spontaneous, asymptomatic microruptures of hepatic cysts into the peritoneal cavity are not uncommon (12% of cases) (11). CT and MR imaging are the modalities of choice in the evaluation of all abdominal structures. HCs are generally multiple and can arise anywhere in the peritoneal cavity. The differential diagnosis can be made easily owing to the characteristic appearance of daughter cysts (Fig 11), but unilocular type I HCs may be difficult to differentiate HCs from mesenteric cysts or intestinal duplication cysts. Any form of HC can be seen in the peritoneal cavity. Moreover, HCs can be located anywhere in the peritoneal cavity (eg, in a herniated umbilical sac) (Fig 12).
View larger version (146K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11. Peritoneal HD in a 47-year-old man who had previously undergone surgery for a hepatic HC. Axial contrast-enhanced CT scan through the middle pole of the kidneys shows multiple low-attenuation daughter cysts in the peritoneal cavity.
|
|
View larger version (125K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12a. Intraperitoneal HCs and a herniated umbilical sac in a 55-year-old man with a previous history of liver HD. (a) Axial breath-hold fast spin-echo T1-weighted MR image shows multiple low-signal-intensity lesions within the mesenteric fatty tissue. Note also the umbilical hernia and the low-signal-intensity masses within the herniated sac. (b) Corresponding axial rapid acquisition with relaxation enhancement T2-weighted MR image shows multiple areas of increased signal intensity. The hypointense rim sign characteristic of HCs is best seen with this sequence. Note also the multivesicular hepatic cyst within the herniated sac.
|
|
View larger version (135K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12b. Intraperitoneal HCs and a herniated umbilical sac in a 55-year-old man with a previous history of liver HD. (a) Axial breath-hold fast spin-echo T1-weighted MR image shows multiple low-signal-intensity lesions within the mesenteric fatty tissue. Note also the umbilical hernia and the low-signal-intensity masses within the herniated sac. (b) Corresponding axial rapid acquisition with relaxation enhancement T2-weighted MR image shows multiple areas of increased signal intensity. The hypointense rim sign characteristic of HCs is best seen with this sequence. Note also the multivesicular hepatic cyst within the herniated sac.
|
|
Isolated retroperitoneal HCs are also rare and are secondary to the involvement of other organs—especially the liver—or to surgery (10,11). There were two cases of retroperitoneal HC in our series. The HC was secondary to previous surgery in one case; however, in the other case, we were unable to find any other organ involvement. The imaging appearances were similar to those of HCs located elsewhere in the body. Any type of HC can be seen in the retroperitoneum (Fig 13).
View larger version (126K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13a. Type II retroperitoneal HC. (a) Axial contrast-enhanced CT scan through the pelvis shows an HC with daughter cysts adjacent to the left iliac muscle. In this case, HD was secondary to liver involvement and previous surgery. (b) Axial contrast-enhanced CT scan through the pelvis shows a hypoattenuating mass that contains detached membranes with a serpentine appearance adjacent to the left psoas muscle. The mass represents isolated retroperitoneal involvement.
|
|
View larger version (123K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13b. Type II retroperitoneal HC. (a) Axial contrast-enhanced CT scan through the pelvis shows an HC with daughter cysts adjacent to the left iliac muscle. In this case, HD was secondary to liver involvement and previous surgery. (b) Axial contrast-enhanced CT scan through the pelvis shows a hypoattenuating mass that contains detached membranes with a serpentine appearance adjacent to the left psoas muscle. The mass represents isolated retroperitoneal involvement.
|
|
Bladder.—
Urinary tract and bladder involvement can occur secondary to kidney HCs. If an HC ruptures into the collecting system, the disease can spread to the ureters or bladder. However, primary HD of these structures is extremely rare (9). There have been some reports in the literature of retrovesical HD caused by urinary retention (12). In our series, we found only one case of HCs located in the bladder. The patient was a 53-year-old woman who had suffered from liver and peritoneal HCs for several years and had previously undergone repeated surgeries. There were three HCs at different growth stages in the bladder and no HCs in the kidneys. One of the cysts originated from the anterior wall of the bladder. The other two cysts were located in the posterolateral wall and protruded into the lumen of the bladder; one demonstrated dense circumferential calcification, whereas the other demon-strated stippled calcification within the lesion (Fig 14). The HC that originated from the anterior wall of the bladder mimicked pseudodiverticulum formation; the other two simulated bladder carcinoma. There was also a solitary unilocular HC in a retrovesical location. The diagnosis of HC was made at surgery.
View larger version (103K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14a. Secondary involvement of the bladder and retrovesical areas in a 53-year-old woman with a multiyear history of liver and peritoneal HCs. The patient had undergone repeated surgeries. (a) Axial contiguous contrast-enhanced CT scan through the lower pelvis shows low-attenuation masses in the left retrovesical area. The posterolateral bladder wall is seen to protrude into the lumen of the bladder. Note the intralesional calcification, which originates at the right posterolateral wall. In addition, there is a second, densely calcified lesion within the bladder lumen (type III hepatic cyst). (b) Axial contrast-enhanced CT scan obtained 10 mm distal to a shows a hypoattenuating mass with dense peripheral calcification that protrudes into the bladder lumen. (c) Axial contrast-enhanced CT scan obtained 10 mm distal to b shows a third low-attenuation mass that protrudes from the anterior wall of the bladder.
|
|
View larger version (112K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14b. Secondary involvement of the bladder and retrovesical areas in a 53-year-old woman with a multiyear history of liver and peritoneal HCs. The patient had undergone repeated surgeries. (a) Axial contiguous contrast-enhanced CT scan through the lower pelvis shows low-attenuation masses in the left retrovesical area. The posterolateral bladder wall is seen to protrude into the lumen of the bladder. Note the intralesional calcification, which originates at the right posterolateral wall. In addition, there is a second, densely calcified lesion within the bladder lumen (type III hepatic cyst). (b) Axial contrast-enhanced CT scan obtained 10 mm distal to a shows a hypoattenuating mass with dense peripheral calcification that protrudes into the bladder lumen. (c) Axial contrast-enhanced CT scan obtained 10 mm distal to b shows a third low-attenuation mass that protrudes from the anterior wall of the bladder.
|
|
View larger version (101K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14c. Secondary involvement of the bladder and retrovesical areas in a 53-year-old woman with a multiyear history of liver and peritoneal HCs. The patient had undergone repeated surgeries. (a) Axial contiguous contrast-enhanced CT scan through the lower pelvis shows low-attenuation masses in the left retrovesical area. The posterolateral bladder wall is seen to protrude into the lumen of the bladder. Note the intralesional calcification, which originates at the right posterolateral wall. In addition, there is a second, densely calcified lesion within the bladder lumen (type III hepatic cyst). (b) Axial contrast-enhanced CT scan obtained 10 mm distal to a shows a hypoattenuating mass with dense peripheral calcification that protrudes into the bladder lumen. (c) Axial contrast-enhanced CT scan obtained 10 mm distal to b shows a third low-attenuation mass that protrudes from the anterior wall of the bladder.
|
|
Ovary.—
Ovarian HD is rare, with only a few reported cases in the literature. Involvement of the ovaries is generally secondary to peritoneal spread of daughter cysts due to rupture of a liver HC. Isolated primary ovarian involvement has been reported (13). Ovarian HCs may remain asymptomatic for a long time and be discovered incidentally or may cause irritation or compression symptoms. It is very difficult to differentiate HCs from other ovarian lesions that may appear to be mostly cystic (cystadenoma, cystadenocarcinoma) on the basis of imaging findings alone. HCs may be unilocular (Fig 15) and can mimic an ovarian cystadenoma, especially in women of reproductive age. Daughter cysts can simulate septal structures that may be seen in cystadenocarcinoma. In our series, we found only a right ovarian HC with a unilocular type I appearance. The diagnosis was made at surgery.
View larger version (110K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 15. Incidentally found HD with primary ovarian involvement in a 38-year-old woman. Axial contrast-enhanced CT scan shows a low-attenuation lesion in the right ovary. The cyst is unilocular and cannot be differentiated from an ovarian cystadenoma on the basis of CT findings alone. Because of the increasing size of the lesion at follow-up, the patient underwent surgery, which revealed an HC.
|
|
Scrotum.—
To our knowledge, there have been no reports of an HC of the scrotum. Only a few case reports of HD of the testis are found in the literature (14). Scrotal HD is extremely rare; we detected only one case in our series. In this case, the patient presented with acute scrotal pain. He described a mobile scrotal mass of 5 months duration that suddenly lost its spheric shape. The scrotum began to swell diffusely and became more painful. US revealed a markedly anechoic fluid collection in the left side of the scrotum and freely floating isoechoic serpentine structures (Fig 16). These findings raised suspicion for HC, and when we evaluated other organs, we found multiple HCs in the liver and intraperitoneum. The diagnosis was confirmed at surgery.
View larger version (143K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16. HD with secondary scrotal involvement in a 63-year-old man with multiple HCs in the liver and peritoneum. The patient presented with acute scrotal pain. US image shows a well-demarcated fluid collection with freely floating isoechoic serpentine structures in the left side of the scrotum. These structures were suggestive of the rupture and detached membranes of an HC. Surgery helped confirm the diagnosis.
|
|
Thorax
Lung.—
The lung is the second most common site of hematogenous spread in adults and probably the most common site in children (15%–25% of cases). Pulmonary HCs have a predilection for the right posterior lung segments, with 60% of cases manifesting in the lower lobes. Bilateral involvement occurs in 20% of cases and multiple cysts in 30% (Fig 17). The number of HCs can vary from two to 60. Concurrent involvement of the liver and lungs is seen in ap-proximately 6% of all patients with HCs in thoracic and abdominal organs (15). Pulmonary HCs may vary from 1 to 20 cm in diameter. Because of their compressibility, the lungs are the only organ in which HCs can grow so large. The high prevalence of pulmonary HC in childhood can also be attributed to this feature (Fig 18).The lung tissue and immune system of the host in childhood and adolescence allow rapid cyst growth, and giant HCs are frequently seen in pediatric patients.
View larger version (132K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 17. Multiple lung HCs in a 28-year-old man. Posteroanterior chest radiograph shows multiple well-defined areas of increased opacity in both lung fields. Note also the thin-walled cavitary lesions in the right lower and bilateral upper zones (arrows).
|
|
View larger version (131K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 18. Giant HC of the left lung with concomitant liver involvement in a 4-year-old boy. Multiplanar reformatted CT scan shows a giant HC (arrowheads) that occupies almost the entire left lung. A second giant HC (arrows) occupies nearly all of the right hepatic lobe. The compressibility of these organs allows HCs to grow this large.
|
|
Imaging appearances may vary due to the growth of the parasite and its relationship to adjacent lung tissue. Initially, lung HCs generally manifest as type I cysts, being oval or round and having well-defined borders. CT reveals the hypoattenuating nature of these lesions (HU values are consistent with those of fluid). Diagnosis is generally easily made in endemic regions on the basis of typical location and imaging findings, but multiple HCs can be misdiagnosed as metastases (Fig 17). Daughter cysts (type II) are rarely seen in lung HD (16). One of the most common imaging findings in HC is the "meniscus sign," which occurs when cyst growth produces erosions in the bronchioles that are included in the pericyst; as a result, air is present between the pericyst and the laminated membrane. Air between the endocyst and pericyst creates the "onion peel sign" (Fig 19a). If air continues to enter the cyst cavity, the two layers completely separate from each other. The collapsed and crumpled endocyst floats freely in the most dependent part of the pericyst cavity and produces the "water lily sign" (Fig 19b). Calcification in pulmonary HC is very rare (0.7% of cases). The other unusual finding in pulmonary HCs is a thin-walled translucent or cavitary lesion containing air. This finding generally occurs during medical treatment of HC (Fig 17): Antiparasitic drugs cause the detachment of the membranes and cell autolysis; as a result of autolysis, the cyst wall comes into contact with the bronchial tree and air entrapment occurs. This finding can also be seen during the natural course of HC without medical therapy (17).
View larger version (92K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19a. Ruptured type IV HC of the lung. (a) Axial CT scan obtained through the mediobasal segment of the right lung in an 18-year-old man shows the onion peel sign created by air that is trapped between the endocyst and pericyst. Note also the parenchymal consolidation adjacent to the HC. (b) Axial CT scan obtained through the apical segment of the left lower lobe in a 44-year-old woman shows the water lily sign created by collapsed and crumpled endocysts floating freely in the most dependent part of the cyst.
|
|
View larger version (93K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19b. Ruptured type IV HC of the lung. (a) Axial CT scan obtained through the mediobasal segment of the right lung in an 18-year-old man shows the onion peel sign created by air that is trapped between the endocyst and pericyst. Note also the parenchymal consolidation adjacent to the HC. (b) Axial CT scan obtained through the apical segment of the left lower lobe in a 44-year-old woman shows the water lily sign created by collapsed and crumpled endocysts floating freely in the most dependent part of the cyst.
|
|
Complications of lung HC include rupture of the cyst into the parenchyma and pleural cavity. Rupture of an HC into the lung parenchyma produces consolidation surrounding the cyst (Fig 19a). The other complication of HC is recurrent acute pulmonary embolism, a rare complication that can be seen when a cyst directly involves the vena cava.
Pleura.—
Pleural HD is generally secondary to lung involvement and may be due to an HC that arises in the liver and prolapses into the chest, but on rare occasions it may be primary. Pleural HCs may be solitary or multiple. Multiple pleural involvement is seen in cases of lung HC rupture.
The imaging features of pleural HC change with the growth of the parasite. Type I or type II (Fig 20) HCs may be seen (18,19).
View larger version (108K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 20a. Primary HD of the pleura. Axial CT scans obtained through the lungs in two different patients show low-attenuation masses with daughter cysts in the left pleura, findings that represent type IIB (a) and type IIA (b) HCs.
|
|
View larger version (113K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 20b. Primary HD of the pleura. Axial CT scans obtained through the lungs in two different patients show low-attenuation masses with daughter cysts in the left pleura, findings that represent type IIB (a) and type IIA (b) HCs.
|
|
Mediastinum.—
The larvae of HCs are rarely present in the mediastinum, although approximately 108 cases have been reported in the literature. Like HCs located elsewhere in the body, mediastinal HCs affect both sexes equally and can be seen in patients of all ages. The symptoms of mediastinal HC depend on the size and location of the cyst and the involvement of adjacent structures. It may be primary or can spread through the mediastinum during the rupture of lung HC. Mediastinal involvement may be solitary or multiple, depending on the type of occurrence. The imaging appearance can vary from type I to type III (Fig 21) (3,20,21). Type II and type III HCs in the anterior mediastinum should be differentiated from thymoma and teratoma that have mostly necrotic components. CT and MR imaging are the preferred examination methods for the evaluation of mediastinal HC.
Heart and Pericardium.—
Heart HD is very rare (0.02%–2% of cases) and may be due to hematogenous spread or rupture of a lung HC (22,23). The most commonly affected cardiac chambers (in decreasing order of frequency) are the left ventricle (50%–60% of cases), interventricular septum (10%–20%), right ventricle (5%–15%), pericardium (10%–15%), and right or left atrium (5%–8%) (24).
Deformation of the cardiac borders, especially by large HCs, can be seen at chest radiography. Transthoracic echocardiography, CT, and MR imaging can show the cystic nature of the mass and its relationship to the cardiac chambers. Transthoracic echocardiography may be inadequate to define the cyst and its relationship to adjacent structures. The cyst may be unilocular (type I) or multivesicular (type II) in appearance (Figs 22, 23). Cardiac motion artifact is an important limitation of CT in the evaluation of heart HC. Cardiac-gated MR imaging provides information, not only about the internal structure of HCs, but also about the effects of the cyst on cardiac function.
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 22. HD of the heart in a 43-year-old man. Axial contrast-enhanced CT scan shows a low-attenuation mass in the left ventricle, a finding that is consistent with type I unilocular HC.
|
|
View larger version (140K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 23. HD of the heart in a 28-year-old woman. Transverse US image shows a multiloculated anechoic mass with daughter cysts in the right ventricle (arrows), a finding that is consistent with type IIB HC. IVN = interventricular septum, LV = left ventricle, RA = right atrium, RV = right ventricle.
|
|
Pericardial HCs are generally located in the right costophrenic recess; however, unusual locations such as the left costophrenic recess, the hila, and the superior mediastinum at the level of the aortic arch may also be encountered. Pericardial HCs produce deformation of the lung contours at chest radiography (Fig 24a). As with heart HCs, CT is of limited value in the evaluation of pericardial HCs due to motion artifact. However, adequate contrast material filling within the cardiac chambers can provide important information about the location and internal structure of the lesion (Fig 24b). The appearance of HCs located in the heart and pericardium may vary from type I to type III. Cardiac HCs have low signal intensity on T1-weighted MR images (Fig 24c) and high signal intensity on T2-weighted images. The daughter cysts may have either low or high signal intensity depending on their contents.
View larger version (140K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 24a. HD with pericardial involvement in a 15-year-old boy. (a) Posteroanterior chest radiograph shows deformation of the lung contour at the left border of the heart, which is obscured by a radiopaque lesion. Note also the displacement of the heart to the right. (b) Axial contrast-enhanced CT scan shows a type IIA HC with multiple peripheral daughter cysts. (c) Axial spin-echo T1-weighted MR image also shows a type IIA HC in proximity to the left ventricular wall and displacing the heart to the right.
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 24b. HD with pericardial involvement in a 15-year-old boy. (a) Posteroanterior chest radiograph shows deformation of the lung contour at the left border of the heart, which is obscured by a radiopaque lesion. Note also the displacement of the heart to the right. (b) Axial contrast-enhanced CT scan shows a type IIA HC with multiple peripheral daughter cysts. (c) Axial spin-echo T1-weighted MR image also shows a type IIA HC in proximity to the left ventricular wall and displacing the heart to the right.
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 24c. HD with pericardial involvement in a 15-year-old boy. (a) Posteroanterior chest radiograph shows deformation of the lung contour at the left border of the heart, which is obscured by a radiopaque lesion. Note also the displacement of the heart to the right. (b) Axial contrast-enhanced CT scan shows a type IIA HC with multiple peripheral daughter cysts. (c) Axial spin-echo T1-weighted MR image also shows a type IIA HC in proximity to the left ventricular wall and displacing the heart to the right.
|
|
Head and Neck
Brain.—
Cerebral HC is extremely rare, accounting for only 2% of all intracranial masses, even in countries where this disease is endemic. HCs are mostly located in the territories of the middle cerebral artery but can be seen anywhere within the brain. Most cysts are supratentorial. The parietal lobe is most frequently involved. Cerebral HC is more common in children than in adults (25).
At radiology, cerebral HC generally appears unilocular and is isointense or isoattenuating rela-tive to cerebrospinal fluid (Fig 25). Fine peripheral enhancement can be seen in the fibrous capsule. The lack of surrounding edema and the marked mass effect make it easy to distinguish cerebral HC from abscess and cystic tumor. The presence of a hypointense rim, especially on T2-weighted MR images, is characteristic of HC of the brain. Cerebral HC is generally solitary but may be multiple when it ruptures spontaneously or due to trauma or surgery. Multivesicular cysts are rare in the brain (Fig 26). Calcification occurs in less than 1% of cases.
View larger version (125K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 25. Type I HC of the brain in a 12-year-old boy. Axial CT scan shows a mass in the left parietal lobe with an attenuation similar to that of cerebrospinal fluid. Note the mass effect and the displacement of the interhemispheric fissure to the right. There is no edema formation adjacent to the cyst.
|
|
View larger version (128K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 26a. Type IIB HC of the brain in a 17-year-old girl with erosion of the adjacent calvaria. (a) Contrast-enhanced T1-weighted MR image shows a nonenhancing, low-signal-intensity multiloculated mass without edema formation in the right parietal lobe. Note also the mass effect. (b) Axial T2-weighted MR image shows increased signal intensity within the lesion. Daughter cysts are seen that are somewhat hypointense relative to the mother cyst. Note also the low-signal-intensity rim surrounding the daughter cysts. (c) Sagittal T1-weighted MR image clearly delineates the erosion of the parietal bone and the HC protrusion into the subgaleal fatty tissue. (d) Lateral radiograph of the skull shows a radiolucent lytic lesion in the parietal bone. Minimal sclerotic changes are seen at the periphery of the lesion.
|
|
View larger version (108K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 26b. Type IIB HC of the brain in a 17-year-old girl with erosion of the adjacent calvaria. (a) Contrast-enhanced T1-weighted MR image shows a nonenhancing, low-signal-intensity multiloculated mass without edema formation in the right parietal lobe. Note also the mass effect. (b) Axial T2-weighted MR image shows increased signal intensity within the lesion. Daughter cysts are seen that are somewhat hypointense relative to the mother cyst. Note also the low-signal-intensity rim surrounding the daughter cysts. (c) Sagittal T1-weighted MR image clearly delineates the erosion of the parietal bone and the HC protrusion into the subgaleal fatty tissue. (d) Lateral radiograph of the skull shows a radiolucent lytic lesion in the parietal bone. Minimal sclerotic changes are seen at the periphery of the lesion.
|
|
View larger version (154K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 26c. Type IIB HC of the brain in a 17-year-old girl with erosion of the adjacent calvaria. (a) Contrast-enhanced T1-weighted MR image shows a nonenhancing, low-signal-intensity multiloculated mass without edema formation in the right parietal lobe. Note also the mass effect. (b) Axial T2-weighted MR image shows increased signal intensity within the lesion. Daughter cysts are seen that are somewhat hypointense relative to the mother cyst. Note also the low-signal-intensity rim surrounding the daughter cysts. (c) Sagittal T1-weighted MR image clearly delineates the erosion of the parietal bone and the HC protrusion into the subgaleal fatty tissue. (d) Lateral radiograph of the skull shows a radiolucent lytic lesion in the parietal bone. Minimal sclerotic changes are seen at the periphery of the lesion.
|
|
View larger version (132K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 26d. Type IIB HC of the brain in a 17-year-old girl with erosion of the adjacent calvaria. (a) Contrast-enhanced T1-weighted MR image shows a nonenhancing, low-signal-intensity multiloculated mass without edema formation in the right parietal lobe. Note also the mass effect. (b) Axial T2-weighted MR image shows increased signal intensity within the lesion. Daughter cysts are seen that are somewhat hypointense relative to the mother cyst. Note also the low-signal-intensity rim surrounding the daughter cysts. (c) Sagittal T1-weighted MR image clearly delineates the erosion of the parietal bone and the HC protrusion into the subgaleal fatty tissue. (d) Lateral radiograph of the skull shows a radiolucent lytic lesion in the parietal bone. Minimal sclerotic changes are seen at the periphery of the lesion.
|
|
The mass effect of HC is very prominent in the brain, and symptoms are generally due to compression of vital cerebral structures. HCs located in proximity to the cortex can protrude into the meninges and calvaria and cause erosion (Fig 27). Pontine, intraventricular, meningeal, cavernous sinus, aqueduct of sylvius, cerebellar, skull, and intracellular locations have been reported for HD but are extremely rare (25). Rupture and infection are important complications of HD of the brain. When HCs are infected, the lesions show enhancement after contrast material injection, and differential diagnosis is sometimes difficult (Fig 27).
View larger version (156K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 27a. Multiple infected HD of the brain in a 23-year-old man. The patient had previously undergone surgery for a cerebral HC. (a) Axial T1-weighted MR image shows multiple low-signal-intensity lesions in the occipital lobes bilaterally. (b) Axial contrast-enhanced T1-weighted MR image shows enhancement peripheral to the lesions, a finding that is consistent with infection. (c) T2-weighted MR image demonstrates mixed heterogeneous signal intensity in the occipital lobes. Note also the edema formation, an unusual finding in HC of the brain.
|
|
Top
Abstract
LEARNING OBJECTIVES FOR TEST...
