Hydatid disease has a worldwide distribution and causes health problems in endemic countries, including china. The disease most often affects liver and lung. Only 0.5-2% is located in the skeletal system,and in approximately 50% of these cases the spinal column is involved [6, 7]. Spinal hydatid cysts are usually situated in the dorsal region and generate medullary or radicular symptoms according to their location [3, 8, 9]. Primary intraspinal extradural hydatid cysts are very rare.
Primary hydatid disease suggests that the parasite's embryo is possibly being carried through the porto-vertebral venous shunts. The growth of hydatid cyst occurs along the intratrabecular spaces with small diverticulated cysts that are formed by exogenous vesiculation [10]. Enlargement and spread of hydatid cyst may result in local erosion of bone. Finally, Pain, deformity, and weakness may result from either collapse of the spine or by extension of hydatid cysts into the spinal canal [6, 11]. Neurological deterioration is usually very slow, but will result in paraplegia in 25-50% of cases [12].
Spinal hydatid disease may easily be confused with tuberculous spondylitis in some areas where tuberculosis is endemic. A typical characteristic of tuberculous spondylitis is in paradiscal lesion with disc-space narrowing. Paraspinal extension is very common, with calcification in the mass being pathognomonic for tuberculous infection. Hydatid disease usually involved in the thoracic and lumbar regions where are also typical locations for tuberculous spondylitis. Therefore, the two entities may mimic each other, making differential diagnosis difficult.
MRI may show important differences and aid in early diagnosis and treatment. MRI imaging revealed precise anatomic localization and extension of the spinal hydatid disease. In this case, Cysts had thin walls and CSF-like signal intensity on MR images. On T2-weighted images, cyst scoleces appeared more hyperintense, whereas small vesicles and daughter cysts were visible in a bunch-of-grapes pattern. MRI showed the cysts had a liquid component tendency to invade anatomical cavities through the neural foramen. CT scanning may be more convenient and more advantageous in following the progress of bone lesions associated with this disease. Although plain radiographs can show in the advance stage the bone destruction, the radiological features are not pathognomonic [13]. This case suggested that the differential diagnosis may be preferred on MR images because of the multicystic nature of the disease. CT scanning provided a precise assessment of the osseous part of the lesion and the calcifications of the cyst. And MRI was the superior method in the diagnosis in involvement of neural structures, extension into the soft tissues. Consequently, CT and MRI may be complementary methods in the evaluation of primary intraspinal extradural hydatid disease.
Hydatid cyst can be diagnosed by means of the anamnesis if the patient originates from a region where the disease is endemic, or by serological tests. But it is known that the Casoni-Weinberg test is not very reliable [14]. In this present case, the serological tests were negative. Due to the stated clinical history (from Xinjiang province, epidemic area of China) and typical neuroradiological features, spinal hydatid cysts should be considered. The final diagnosis is also confirmed by histopathological examination.
Spinal hydatid disease should be carefully considered when planning a surgery especially in endemic countries. Treatment should be surgical removal without cyst rupture and medical therapy (mebendazole or albendazole) following the surgery. Generally, the major factor influencing the choice of surgical approach is the degree of neuro-foraminal and spinal canal involvement. Antihelminthic drugs should be given for longer periods up to 2 years after surgery [15]. In our case, an anterior approach was adequate for exposure and removal of the lesions. A posterior approach was not considered because we wanted to keep the posterior spinal column mechanically strong and reduced the risk of posterior spread of the infestation. Misdiagnosis of spinal hydatid cyst as tuberculous spondylitis could result in serious consequences. Recurrence (30% 100%) remains a major problem in spinal hydatid disease [16, 17]. Long-term hydatid disease caused persistent pain, significant persistent neurologic deficits and spinal instability and resulted in a high morbidity and mortality and poor prognosis. Albendazole treatment should be started in the postoperative stage, preventing late recurrences.