A 49-year-old female patient presented with a 2-year history of progressive right lumbar pain radiating to her right lower extremity. The pain, which originated in the right buttock, extended down the posterior aspect of the right thigh and the calf to the ankle. She was operated on for the right ovarian hydatid cyst 16 years before. There was no history of prior trauma.

On admission, the neurological examination revealed hypoesthesia, a slight weakness and atrophy of the abductor and extensor of the hip and the flexor muscles of the knee, and areflexia and radicular pain of the right leg. Treatment that included anti-inflammatory drugs and exercise did not alleviate the pain. Therefore, a possibility of lower lumbar disc herniation was considered. An MRI examination that was intended to detect lumbar disc herniation was performed. The MRI of the lumbar spine showed no nerve-root compromise, but on the very right parasagittal images, a globular, septated cystic lesion in the right side of the pelvis was noticed (Fig. 1).

A review of the axial computed tomographic (CT) scan of the pelvis showed a multiloculated cystic mass located in the right presacral area (Fig. 2). According to the pelvic MRI, the multiloculated cystic lesion was located anterior to the right sacral foraminae. The lesion had low T1 and high T2 signal intensities, without contrast enhancement. Besides this right-sided cyst, there was another lesion with the same imaging characteristics in the posterior left side of the rectum (Fig. 3A). The right-sided lesion was in close proximity to the sacral nerve fibers. On the oblique coronal views, the displacement and compression of the lumbosacral nerve trunk could be well seen (Figs. 3B, C). There was no expansion or destruction in the bony structure of the foraminae.

Because of the previous history of the right-sided oophorectomy due to hydatid disease, the patient was operated on with the presumptive diagnosis of hydatid disease. The diagnosis of a hydatid cyst was confirmed histologically after surgical removal of the lesion. At the time of the operation, the sacral nerve trunk was found to be displaced and compressed by the right-sided presacral cyst. Mebendazole (100 mg twice daily for 4 months) was prescribed.

Hydatid disease (echinococcosis), is a parasitic infection that's caused by a cestode Echinococcus, mostly the form of E. granulosus (1). Hydatid cysts are noted throughout the world, but they are widespread in endemic regions. Echinococcal eggs of the adult worm are present in the small intestine of canine animals, and they are excreted with the feces. When ingested by intermediate hosts like sheep, cattle or humans, these eggs hatch in the intestine of these intermediate hosts. Then the eggs, in the form of oncospheres, penetrate through the mucosa of the intestine and diffuse into the blood and lymphatic circulation. They are transported by the circulation to the organs, mostly to the liver and lungs, where they grow and produce cysts. Hydatid cysts are seldom primary in other organs, and they are often part of generalized disease. Involvement of the pelvis in hydatid disease is reported to be ≤2% (2-5). In female, genital organs are reported to be the most affected areas in pelvis which can be attributed to their relatively ample bloodstream and true invasions from connective tissue of peritoneum of Douglas and suspensory ligaments (2, 6) Pelvic hydatid disease can be presented with vague abdominal pains due to irritation, swelling, menstrual irregularities, infertility and pressure symptoms involving the adjacent organs (bladder, ureters, rectum and vascular structures) (2, 4, 7-9). Symptoms indicative of compression of the lumbosacral plexus, as in our case, are really quite infrequent, and on very few occasions they have been reported (4-6). In the case of Martin-Serradilla et al. (4), a pelvic hydatid cyst compressing the lumbosacral nerve plexus and the gluteal veins was shown by CT. Hassan et al. (5) documented a pelvic hydatid cyst causing erosion in the roof of the sacral foramina, extending down to the coccygeal spine and causing swelling in the gluteal region, by CT.

The pelvic hydatid cyst in the case of Gupta et al. (6) was located in the right pelvis, and it extended through the greater sciatic notch into the gluteal region.

The recurrence incidence of hydatid disease after surgery is said to be 8-22% with recurrences most often noted within 2 years after the operation (2). Our patient was operated on 16 years ago. This shows that the hydatid cyst may recur many years after the operation.

It is not infrequent to confront with sciatica in daily practice of outcome patients in related departments. Lumbar disc herniation affecting the lower lumbar root nerves is usually the reason of sciatica (5). Adnexial masses like endometrioma, acetabular labral cysts, iliopsoas bursal cysts and pelvic hydatid cysts, as in our case, are other rare pathologies that may compress the lumbosacral plexus and cause sciatica (10-12).

In this patient, the hydatid cyst operation history was the main clue that helped make the correct diagnosis in a short time. Nevertheless, cyst formation may primarily take place in the pelvis, may be discovered incidentally, or cause irritation and compression symptoms and may cause diagnostic dilemma (2).

This case demonstrates two important points. First, pelvic masses that include hydatid cysts may cause sciatica; second, radiologist should be familiar with hydatid cyst imaging features and direct the surgeon, so that careful attempts be made during operation in order to prevent recurrences and choose the appropriate treatment options.

This parasite should be kept in mind and considered when making the differential diagnosis of pelvic cystic masses, in particularly if the patient is from an endemic area. Along with their diverse symptomatology, pelvic hydatid cysts may also cause sciatica.

In conclusion, if no pathology is evident for the lumbar discal structures, in connection with the cause of sciatica and lumbar back pains, then the pelvis should also be examined for the possible etiologies of compression of the lumbosacral nerve plexus. Whenever a multiseptated cyst is come across in a patient of an endemic origin with a positive history for hydatid disease like surgery, indicating recurrence, hydatid cyst is the most likely diagnosis.