Skeletal Radiol (1993) 22:511-514

Skeletal Radiology

Hydatid disease of the soft tissues of the lower limb: findings in three cases Julio Martin, M.D. l, Vicente Marco, M.D. 3, Ahmed Zidan, M.D. 1, Constancio Marco, M.D. 2

1 Unitat de Diagn6stic per la Imatge d'Alta Tecnologia (UDIAT), Sabadell, Barcelona, Spain 2 Department of Orthopedic Surgery, Instituto Policlinico, Barcelona, and Department of Pathology, 3 Hospital General de Catalunya, Barcelona, Spain

Abstract. Three cases of hydat id disease are reported, all presenting as soft tissue lesions in the lower extremities. All three cases were studied with u l t rasound (US), two with compu ted t o m o g r a p h y (CT), and two with magnet ic resonance (MR) imaging techniques. Two patients pre- sented with multivesicular lesions which were considered diagnostic of hydat id disease. The third patient showed a lesion with a p redominan t ly solid pattern, closely mim- icking a soft-tissue neoplasm. US was not diagnostic, but M R outlined vesicular structures and a fibrous pericyst. Hyda t id disease presenting in the soft tissues can there- fore be diagnosed with confidence when it shows multi- vesicular lesions but M R m a y be the mos t useful imaging technique when a complex or solid pat tern is present.

Key words: Echinococcosis - Soft tissues, computed to- m o g r a p h y - Soft tissues, magnet ic resonance - Soft tis- sues, u l t rasound - hydat id disease

Case reports

Case 1

A 39-year-old man presented with a large mass on the inner aspect of the left thigh. The mass had increased in size over the last 3 months. Past history and laboratory tests were unremarkable. On physical examination the mass was soft and non-tender, it ex- tended from the groin to the middle third of the left thigh. Ultra- sonography, with a 7.5-MHz transducer, showed a large, well-de- lineated mass, with multiple small, round, anechoic cysts through- out (Fig. I a). Enhanced CT examination disclosed a large, hypo- dense, bilobulated mass involving the soft tissues of the proximal and medial aspects of the left thigh, with small, rounded, slightly unenhanced zones (Fig. 1 b). Serology was positive for echinococ- cosis.

At surgery, a large multilobated mass measuring 18 x 14 x 7 cm was excised. The outer surface showed a fibrous capsule. On section it showed multiple vesicles, floating on clear fluid. The pathological diagnosis was intramuscular hydatid disease with foreign body type granulomas.

Hyda t id disease is c o m m o n in m a n y parts o f the world. Two forms o f Echinococcus t apeworm produce disease in humans , E. granulosus, and, less frequently, E. multi- locularis. E. granulosus is c o m m o n in East Africa, in the Medi te r ranean countries, in Russia, and in some parts o f South America. A n y viscus can be involved, the liver and the lung being the mos t f requent sites. Hy- dat id disease o f the soft tissues is u n c o m m o n and in- volves p redominan t ly the skeletal muscles [4, 10, 13]. U l t r a s o n o g r a p h y (US), c o m p u t e d t o m o g r a p h y (CT), and magnet ic resonance (MR) images m a y provide use- ful diagnostic and topograph ic informat ion.

In this repor t we describe the imaging and pathologi- cal findings in three cases o f hydat id disease, presenting in the soft tissues.

Correspondence to: Julio Martin, UDIAT, Parc Tauli s/n. 08208, Sabadell, Barcelona, Spain

Case 2

A previously healthy 40-year-old woman presented with severe pain and swelling of the left thigh. Physical examination showed a soft, tender mass in the posterior aspect of the left thigh.

Routine laboratory tests had normal findings. US with a 7.5- MHz transducer revealed a large cystic lesion, within which were innumerable small rounded cysts, mixed with scanty echogenic ma- terial. Serology was positive for E. granulosus. CT examination showed a round, hypodense lesion displacing the muscles of the posterior compartment of the left thigh, with multiple small rounded hypodensities occupying most of the lesion (Fig. 2 a). MR imaging at 0.5 T in axial, sagittal, and coronal planes was per- formed. Tl-weighted images (500/14) showed a multivesicular cyst in the posterior compartment of the left thigh, with a multitude of small rounded daughter vesicles of very low signal filling the entire cyst (Fig. 2b). T2-weighted images (2000/60) showed high signal daughter cysts. A capsule or pericystic membrane was not seen (Fig. 2c).

Treatment with mebendazole (1500 mg/daily) did not alter the size of the lesion, and surgical excision was performed.

At surgery, a large mass was found in the posterior aspect of the thigh, compressing the semitendinosus muscle, and the biceps femoris. The cystic mass was loosely attached to the femur. Patho- logic examination revealed an encapsulated cystic mass measuring

�9 1993 InternationaI Skeletal Society

512 J. Mart in et al. : Hydatid disease of the soft tissues of the lower limb

Fig. 1A, B. Case 1. A Longitudinal ultrasonog- raphy of the left thigh with a 7.5-MHz trans- ducer shows multiple rounded, anechoic, septat- ed cysts occupying the entire lesion. B Enhanced computed tomographic (CT) examination shows a large, bilobulated mass of reduced attenuation involving the medial compartment of the left thigh. Other rounded zones are seen within the mass (arrow) Fig. 2A-D. Case 2. A Unenhanced CT examina- tion shows a multivesicular cyst displacing the muscles of the posterior compartment of the thigh with multiple low-attenuation daughter cysts. B Coronal Tl-weighted magnetic reso- nance (MR) image (500/14) shows multiple, hy- pointense daughter cysts occupying the entire mother cyst. No capsule surrounds the cyst. C Coronal T2-weighted MR image (2000/60) shows a daughter cyst of high signal intensity, but lower than the mother cyst content. D Hy- datid cyst showing externally a thin, partially folded pericyst (arrow). The cyst contains nu- merous vesicles, with translucent membrane (ar- rowheads)

19 x 9 cm. On section, a cystic cavity was found containing yellow, creamy material, admixed with countless hydatid vesicles, which contained clear fluid (Fig. 2d).

Case 3

A 70-year-old man presented with a painless mass that had been present in the right calf for several years. Past history was unre- markable and routine laboratory tests had normal results.

US with a 7.5-MHz transducer showed a well-defined solid mass with a complex echo structure affecting the deep compart- ment of the right calf. M R images at 0.5 T showed a signal of intermediate intensity in a mass in the right calf on Tl-weighted images (460/25). The mass was encapsulated with an incomplete rim of low-signal intensity with a central septum. Small areas of subtle heterogeneity were present (Fig. 3 a). On T2-weighted images (1800/80) the mass showed a significant increase in signal intensity. Small areas of low signal were present (Fig. 3 b).

At surgery, a well-encapsulated mass was identified, located deep to the medial head of the gastrocnemius compressing the muscles and loosely attached to the fascia.

Grossly, the mass measured 6 x 5 cm. It showed a thick fibrous capsule. On section, the cystic cavity was divided by a fibrous septum. It contained thick, ropy, yellowish material with poorly preserved vesicles. Microscopically, the presence of nonviable echinococcal cysts was confirmed.

Serological study for echinococcal disease undertaken postoper- atively was negative.

Discussion

H y d a t i d d i s e a s e c a u s e d b y Echinococcus granulosus m o s t f r e q u e n t l y a f f ec t s t h e l ive r a n d t h e l ung . O n l y 10 % - 1 5 % o f t h e a f f e c t e d p a t i e n t s p r e s e n t l e s i o n s in o t h e r o r g a n s [1]. H y d a t i d d i s e a s e p r e s e n t i n g in t h e s o f t t i s sues h a s

J. Martin et al. : Hydatid disease of the soft tissues of the lower limb 513

Fig. 3A-D. Case 3. A Coronal Tl-weighted MR image (460/25) shows a well-defined mass of intermediate sig- nal intensity, with central septum (arrowhead), occupy- ing the posterior and medial compartments of the right calf. Small, round, low-signal areas can be seen within the mass (small arrow). A low-signal rim is observed (arrow). B Axial T2-weighted MR image (1800/80) shows bright lobulated mass with a low-signal septum and other small areas of reduced signal intensity. C Cross section of the cyst shows a bilocular cavity, di- vided by a fibrous septum (arrowhead). The wall of the cyst shows a thick, fibrous pericystic membrane (arrow). D The contents of the cyst are a thick, yellowish mate- rial with collapsed vesicles (arrows)

been reported to occur in 0.5 %-4.7 % of those affected [41.

The mechanism of cyst formation is well established. Once the embryos reach an organ, they transform into small cysts. The host reacts against the parasites, form- ing a pericyst or adventitia, which consists of fibrous connective tissue containing blood vessels. The cyst wall is a laminated membrane lined by a germinal layer. Daughter cysts arise from the germinal layer, probably by endoproliferation.

The clinical manifestations of hydatid disease are caused by compression of the involved organ. In the soft tissues a palpable mass is the most constant finding and there is a striking predilection for the lower extremi- ties.

The radiologic findings have been well described in the literature. US and CT have been used for the diagno- sis and topographic assessment [3, 8, 11, 12]. Several patterns of disease have been recognized using these techniques, mostly described in the liver; these include the unilocular cyst, the multivesicular lesion and the atypical complex or solid lesion [9]. The multivesicular

lesion is characteristic of hydatid disease, and it presents multiple daughter cysts occupying the mother cyst. The presence of abundant intracystic debris and inflammato- ry changes may alter the typical cystic morphology, transforming it into a complex or solid lesion mimicking a tumor.

In our experience, the radiologic findings in the soft tissues are similar to those described in the liver. Two of our cases showed the characteristic multivesicular ap- pearance, and the third one showed the solid or complex pattern.

Recently published reports indicate that MR imaging may be valuable in the diagnosis of echinococcosis [14, 16]. However the MR features of hydatid disease in the soft tissues have not been reported previously. New signs, such as the " r im sign" or the "serpent sign," can be useful to differentiate hydatid cysts from other lesions [14]. The " r im sign" consists of a low signal intensity rim surrounding the cyst; it represents the peri- cyst. This sign is not specific to hydatid disease - it can be present in other lesions that contain a fibrous capsule or a calcific rim [2, 5-7]. The " r im sign" was

514 J. Martin et al. : Hydatid disease of the soft tissues of the lower limb

not present in our case 2, but an incomplete rim was observed in case 3, probably due to the presence of a thick collagenous pericyst.

The signal intensity of the daughter cysts depends upon their contents, and it may also vary depending on whether the cysts are dead or alive. When the scolices and the embryos die they disintegrate. The cuticles and matrix persist, but the production of hydatid fluid ceases [15]. Two of our cases studied with MR showed daughter cysts which were hypointense on Tl-weighted images and slightly less hyperintense than the matrix of the mother cysts on T2-weighted images.

US and CT were diagnostic in our two patients with multivesicular lesions. These images were similar to those described in the liver and in other viscera. How- ever, MR was superior to US in the diagnosis of the solid lesion, because it outlined the poorly preserved ve- sicular structures.

In conclusion, hydatid disease involving the soft tis- sues shows variable appearances. The multivesicular cysts are similar to those described in the liver. Compli- cated or old cysts may show solid or complex patterns, mimicking a soft-tissue tumor. In these cases MR may be the most reliable diagnostic imaging technique.

Acknowledgment. We thank Marta Sire6 for manuscript prepara- tion.

References

1. Beggs I (1987) The radiology of hydatid disease. AJR 145:639 2. Case records of the Massachusetts General Hospital (1992)

Case 32-1992. N Engl J Med 327:412

3. De Diego J, Lecumberri FJ, Franquet T, Ostiz S (1982) Com- puted tomography in hepatic echinococcosis. A JR 139:699

4. Di Gesu G, Picone A, La Bianca A, Massaro M, Vetri G (1987) Muscular and subcutaneous hydatidosis. Minerva Med 78 : 835

5. Ebara M, Ohto M, Watanabe Yet al. (1986) Diagnosis of small hepatocellular carcinoma: correlation of MR imaging and tu- mor histologic studies. Radiology 159: 371

6. Elizondo G, Weissleder R, Stark DD, Todd GM, Comptom C, Wittemberg J, Ferrucci JT (1987) Amebic liver abscess: diag- nosis and treatment evaluation with MR imaging. Radiology 165:795

7. Hoff FL, Alsen AM, Walden ME, Glazer GM (1987) MR imag- ing in hydatid disease of the liver. Gastrointest Radiol 12:39

8. Lewall DB, McCorkell SJ (1985) Hepatic echinococcal cyst: sonographic appearance and classification. Radiology 155:773

9. Niron EA, Ozer H (1981) Ultrasound appearances of liver hy- datid disease. Br J Radiol 54:335

10. Petrillo G, Mitone P, Barretta S, Loreto C, Beritelli F, Mag- nano DS (1982) Muscular echinococcosis. J Comput Assist To- mogr 6:1197

11. Ramos L, Marcos J, Illanas M (1979) Radiologic aspects of echinococcosis. Radiology 130:21

12. Saksouk FA, Fahl MH, Rizk GHK (1986) Computed tomogra- phy of pulmonary hydatid disease. J Comput Assist Tomogr 10:226

13. Vietri F, Illuminati G, Palumbo P, Gugliemi R (1988) Recur- rent primary hydatidosis of sartorius muscle. Case report. Acta Chir Scand 154: 535

14. Von Sinner WN (1991) New diagnostic signs in hydatid disease; radiography, ultrasound, CT and MR correlated to pathology. Eur J Radiol 12:150

15. Von Sinner WN, Rifal A, Strake L, Sieck J (1990) Magnetic resonance imaging of thoracic hydatid disease: correlation with clinical findings, radiography, ultrasonography, CT and pathol- ogy. Acta Radiol 31:59

16. Von Sinner WN, Strake L, Clark D, Sharif H (1991) MR imag- ing in hydatid disease. AJR 157:741