Imaging in Hydatid Disease: Pictorial Review

Abstract

Hydatid disease (HD) can affect any organ, but most commonly involves liver parenchyma. Complications like rupture/infection can further complicate the scenario. Familiarity with variable imaging appearances of HD is very helpful in making the diagnosis. This may also aid in diagnosis of difficult or atypical cases. We retrospectively reviewed radiologic findings of HD in 11 patients, who presented to our department in last 1 year. There was involvement of the lung, pleura, mediastinum, liver, abdominal cavity, pelvic cavity, ovary, splenic parenchyma, renal parenchyma, spinal cord, and brain, with variable imaging features.

Keywords

hydatid - rupture - infection - complication

Introduction

Echinococcal infection is responsible for hydatid disease (HD), with most commonly involved organ being the liver.[1] Imaging finding of extrahepatic HD frequently simulates those of hepatic HD, as long as rupture, bleeding, and/or superimposed bacterial infection has not occurred.[2] [3] [4] We retrospectively reviewed radiologic findings of HD in 11 patients ([Table 1]), who presented to our department in last 1 year.

Table 1 Demographic details of 11 patients with hydatid cyst

Case no	Age (y)	Gender	Site of hydatid cyst	Clinical history
1	12	F	Liver	Vague upper abdominal pain
2	41	M	Liver	Pain abdomen with obstructive jaundice
3	75	F	Liver	Vague abdominal discomfort in right upper quadrant
4	38	F	Liver	Dyspepsia with abdominal fullness
5	35	F	Liver	Upper abdominal discomfort
6	30	F	Ruptured hepatic hydatid cyst with intrathoracic extension	Shortness of breath, pain right upper abdominal quadrant
7	13	M	Paravertebral space with intraspinal extension	Bilateral lower limb weakness
8	21	F	Abdominal and pelvic cavity	Diffuse mild pain abdomen in the periumbilical region
9	20	F	Renal, lung, right ovary	Mild dysuria, otherwise asymptomatic
10	9	M	Spleen	Upper abdominal discomfort with fullness, abdominal swelling
11	42	F	Brain	Seizures, multiple episodes in one day. New onset seizure disorder with status epileptics

Abbreviations: F, female; M, male.

Imaging Features of Hydatid Disease in Various Organs

Abdomen

• (1) Liver: Liver is the most common involved organ in HD (case no. 1 to 6, [Fig. 1]) with thin-walled lesions having daughter cysts. Differentials can be simple epithelial cyst and polycystic liver or kidney disease, when multiple unilocular cysts are found also in spleen and pancreatic parenchyma.[3] [4]

• (2) Spleen: Not common (0.9–8% cases). It commonly develops through systemic dissemination or intraperitoneal spread from ruptured liver cyst. Isolated splenic involvement is very rare.[5] Imaging characteristics are similar to those of hepatic hydatid cysts (HCs) (case number 10, [Fig. 2]).

• (3) Kidney: Involvement of kidney by HD is uncommon (∼3% of cases). Generally found in upper or lower pole; often solitary and located in the cortex.[6] Uncomplicated HC may create a bulge in renal outline, appearing as rounded mass. Complications can be infection and rupture with hydatiduria.[7] In our case no. 9 ([Fig. 3]), there was no such complaint. There can be misdiagnosis of multilocular HC as cystic nephroma, simple renal cysts, abscess, or cystic variants of renal cell carcinoma.[8]

• (4) Peritoneum and retroperitoneum: Peritoneal HCs are mostly secondary to hepatic involvement.[9] [10] Generally, HCs are multiple and can grow anywhere in the peritoneal cavity. In case of unilocular type I HC, there may be difficulty to differentiate it from mesenteric cyst or intestinal duplication cyst (case no. 8, [Fig. 4]).

• (5) Ovary: HD in ovaries is uncommon, with just few reported cases in literature. Ovarian involvement is normally secondary to peritoneal spread of daughter cysts because of rupture of liver HC. Ovarian HC may remain asymptomatic for long time and be discovered incidentally (similar to case number 9, [Fig. 5]). Differentials are ovarian cystadenoma and cystadenocarcinoma.[7]

• (6) Thorax: Second most common site of hematogenous spread is lung in adults (case 9, [Fig. 6]). Pulmonary HC prefers right posterior lung segments, and it is found in lower lobes in 60% of cases. Bilateral involvement occurs in 20% cases, and multiple cysts in 30%, varying from 1 to 20 cm in diameter, oval or round, hypoattenuating on computed tomography (CT). However, multiple HC can be wrongly diagnosed as metastases.[6] [11]

Fig. 1 Lesions are marked with stars. (A) A 12-year-old female with upper abdominal pain. Axial T2-weighted image (T2WI) shows a well-defined thick-walled round to oval-shaped lesion showing hyperintense signal with multiple irregular T2 hypointense septae and daughter cysts within suggestive of subcapsular hydatid cyst. (B–D) A 41-year-old male with upper abdominal pain and jaundice. A postoperative case of liver hydatid. Axial T2WI (B), coronal T2WI (C), and oblique three-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP) (D) show a T2 hyperintense lesion with internal septae with a peripheral hypointense rim in segment VI of liver, communicating with the right posterior sectoral bile duct which is dilated. (E, F) A 75-year-old female with vague upper abdominal pain. T2WI (E) shows three well-defined T2 hyperintense lesions with multiple T2 hypointense septae/membranes within the liver. These are present in subcapsular location. Abdominal X-ray (F): radiolucent lesion (marked with star) in liver. (G, H) A 38-year-old female with abdominal fullness. Axial (G) and coronal (H) sections on T2WI. Well-defined cystic lesions are seen in medial segment of left lobe with multiple daughter cysts within; another one along inferior hepatic border. T2 hypointense floating membranes are seen within. (I–L) A 30-year-old female with shortness of breath, upper abdominal pain. Axial (I) and coronal (J) T2WI, coronal post-gadolinium (K) and 3D oblique MRCP (L) images. A well-defined subcapsular heterogeneous lesion seen in segment VIII. It shows heterogeneously hyperintense signal on T2WI with thick irregular T2 hypointense walls. No residual parenchyma between the lesion and right hemidiaphragm for a length of ∼3.5 cm. The collection is seen reaching up to the subcapsular surface with rupture and extension into the posterior basal segment of right lower lobe. The surrounding lung parenchyma shows consolidation and mild effusion. (M, N) A 35-year-old female with upper abdominal discomfort. Axial (N) and coronal (M) T2WI. A large smoothly emarginated partially exophytic cystic lesion is seen involving almost the entire right lobe and caudate lobe. It shows predominantly hyperintense content on T2WI with few curvilinear T2 hypointense septa within. It is seen reaching up to subcapsular location with significant thinning of overlying parenchyma.

Fig. 2 A 9-year-old male with upper abdominal swelling on left side. Axial (A) and coronal (B) sections on T2-weighted image (T2WI). A well-defined T2 hyperintense lesion (marked with star) in the splenic parenchyma. Inner walls of lesion appear mildly irregular.

Fig. 3 A 20-year-old female with mild dysuria. Coronal contrast-enhanced computed tomography (CECT) (A) shows a cystic lesion (marked with star) in upper pole of right kidney. No internal solid component or septations, showing peripheral enhancement without any internal solid enhancing component. On ultrasonography (USG) correlation (B, C), well-defined cystic lesion with dependent daughter cysts within is seen (marked with stars).

Fig. 4 A 21-year-old female with mild diffuse pain abdomen. Coronal T2-weighted image (T2WI) (A) shows well-defined T2 hyperintense cystic lesions in the abdominal and pelvic cavity (marked with stars). No internal solid component or septations, showing peripheral enhancement on post-gadolinium image (B) without any internal solid enhancing component.

Fig. 5 A 20-year-old female with mild dysuria. Contrast-enhanced computed tomography (CECT) abdomen showing cystic lesion (marked with star) in the right ovary.

Fig. 6 A 20-year-old female with mild dysuria. Contrast-enhanced computed tomography (CECT) thorax shows a multiloculated cystic lesion (marked with star) in upper lobe of right lung with thin, enhancing internal septations.

Central Nervous System

• (1) Brain: Cerebral HC is very uncommon (∼2%). Maximum cysts are supratentorial. Cerebral HC is generally found in children than adults, unilocular and isointense to cerebrospinal fluid.[10] Lack of marked mass effect and surrounding edema, helps to differentiate cerebral HC from abscess and cystic tumor. It has hypointense rim, particularly on T2-weighted magnetic resonance (MR) images (case number 11, [Fig. 7]). Differential diagnosis can be porencephalic or arachnoid cysts or epidermoid tumors.[10]

• (2) Spinal cord: Very rare involvement (1%) (case number 7, [Fig. 8]). Thoracic spine is mostly involved (50% of cases) with multiple HC. CT and MR imaging exhibits a lesion which resembles cerebrospinal fluid.[10] [12] Contrary to brain HC, spinal HC exhibits no rim enhancement, after contrast material injection.

• (4) Soft tissue: Rare (∼2.3% of all HD).[11] Low-signal-intensity rim is evident on T2-weighted MR images. Multiple HC can be observed due to spontaneous rupture by trauma or surgery (case number 7, [Fig. 8]). This finding is rare in HC situated elsewhere in the body.[12]

• (5) Bone: Rare involvement (in ∼0.5–2% of cases). Parasitized bone has heterogeneous medium to low signal intensity on T1-weighted image (T1WI) and high signal intensity on T2WI (case number 7, [Fig. 8]) with pathologic fractures.[12]

Fig. 7 A 42-year-old female with seizure. Well-defined intra-axial multilobulated septated cerebrospinal fluid (CSF) intensity lesion is seen in left frontal lobe. The lesion is T1 hypointense (A), T2 hyperintense (B) with signal suppression on fluid-attenuated inversion recovery (FLAIR) sequence (C).

Fig. 8 A 13-year-old male with bilateral lower limb weakness. Axial (A) and coronal (B) T2-weighted image (T2WI) and axial post-gadolinium image (C). Ill-defined multicystic T2 hyperintense lesion (marked with star) is seen in prevertebral and left paravertebral space at dorsal spine. Medially it is extending into the extradural space through left neural foramina and is impinging and displacing the cord toward right side. Multiple similar cysts are also seen within the spinal canal in extradural in location. (D) T2WI and (E) axial post-gadolinium images. A loculated lesion is seen in the paraspinal muscles on left side at the level of D8 and D9 vertebral body, showing hyperintense signal on T2WI with peripheral post-gadolinium enhancement. (F) Axial and (G) sagittal T2W images. A multicystic lesion is seen involving the costochondral junction and posterior aspect of left 10th rib laterally, causing its erosion destruction and is displacing the crus of left hemidiaphragm laterally (B). (H) Axial, (I) coronal, and (J) sagittal T2W images and (K) axial post-gadolinium images of spine. A multicystic lesion is seen causing erosion destruction of body, left transverse process, and spinous process of D11 vertebra (marked with stars) causing grade I collapse of D11 vertebra. T2/short-tau inversion recovery (STIR) hyperintense signal is seen involving body of D12 vertebra on the left side adjacent to this lesion.

The World Health Organization-Informal Working Group on Echinococcosis (WHO-IWGE) published its recommendations in 2009.[13] WHO-IWGE gave consensus opinion that cystic echinococcosis (CE) management should be based on an imaging and stage-specific approach ([Table 2]). Surgery is treatment of choice for management of complicated HCs. Surgery is preferred for following indications for liver HC:

Table 2 Imaging findings and stage-specific optimal management of uncomplicated CE

Classification	Imaging findings	Stage-specific optimal management of uncomplicated CE
CL	Unilocular anechoic cystic lesion. No internal echoes or sepatations	No recommendation
CE 1 (Active stage)	Uniformly anechoic cyst with fine internal echoes may only be visible after patient repositioning Internal echoes represent hydatid sand	< 5 cm: ABZ > 5 cm: PAIR + ABZ
CE 2 (Active stage)	Cyst with internal septation. Described as multivesicular, rosette, or honeycomb appearance	Other PT + ABZ
CE 3A (Transitional stage)	Daughter cysts have detached laminated membranes (water lily sign)	< 5 cm: ABZ > 5 cm: PAIR + ABZ
CE 3B (Transitional stage)	Daughter cysts within a solid matrix	Non-PAIR PT + ABZ
CE 4 (Inactive/Degeneration)	Absence of daughter cysts. Mixed hypoechoic and hyperechoic matrix. Resembling a ball of wool	Wait and watch
CE 5 (Inactive/Degeneration)	Arch-like, thick partially or completely calcified wall	Wait and watch

Abbreviations: ABZ, albendazole; CE, cystic echinococcosis; CL, cystic lesion; PAIR, puncture, aspiration, instillation, reaspiration; PT, percutaneous treatment.

• (1) Cysts exerting pressure on adjacent vital organs

• (2) Cysts communicating with biliary tree (alternative to percutaneous treatment [PT])

• (3) Large CE2-CE3B cysts with multiple daughter cysts

• (4) Large single superficial liver cyst that may rupture spontaneously (alternative to PT)

• (5) Infected cysts (alternative to PT)

WHO-IWGE recommended that for alveolar echinococcosis, early diagnosis and radical surgery should be done first, followed by prophylaxis with albendazole. If radical surgery cannot be done, then continuous medical treatment should be done with albendazole.

Conclusion

Familiarity with variable imaging appearances of HD is very helpful in making the diagnosis. This may also aid in diagnosis of difficult or atypical cases.

Conflict of Interest

None declared.

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Publication History

Article published online:
13 January 2025