The disease is endemic in many parts of the world but it is important to be aware of the condition even in non endemic parts of the world, where only occasional cases are encountered, because of the rapid movement of large human groups from endemic to non endemic areas [1]. Radiologists must be familiar with hydatid disease findings.
Cerebral hydatidosis accounts for approximately 1–3% of all cases of hydatid disease [2]. Primary multiple cysts of the brain result from arterial embolism secondary to ingestion of multiple larvae and without any radiological or clinical evidence of hydatid disease elsewhere in the body [3].
It is most commonly seen in children and young adults in approximately 50-70% of cases [3]. Intracranial hypertension and motor weakness due to increased intracranial pressure are the most common clinical manifestations of hydatid disease. Because of their indolent nature, hydatid cysts may not cause focal neurological signs until they are very large [2,3].
Most commonly, cerebral hydatid cysts are single lesions and locate anywhere within the brain, but are especially located in the middle cerebral artery territory. The parietal lobe is the most frequently involved region [1,2].
Hydatid cysts of the brain are usually single, spherical, unilocular, and may be large; in rare instances, they can be multiple and embolic [3].
Both CT and MRI demonstrate a spherical and well-defined, smooth, thin walled, homogeneous cystic lesion with fluid density similar to the cerebrospinal fluid, with or without septations or calcification. The cyst wall usually showed a rim of low signal intensity on both T1- and T2-weighted images. Compression of the midline structures and ventricles are seen in most of the cases, however surrounding oedema and rim enhancement are usually absent in untreated or uncomplicated cases [4].
The differential diagnosis of intracerebral hydatid cysts includes cystic lesions such as porencephalic cyst, arachnoid cyst, cystic tumor of the brain and pyogenic abscess [1]. The hydatid cyst is usually hypointense in diffusion weighted images and Proton MR Spectroscopy demonstrate lactate, alanine and pyruvate within the lesion. Pyruvate is very characteristic of hydatid cyst. This metabolite may be a marker of parasitic etiology and perhaps that of viability of such intracranial cysts [4].
CT scan and MRI are excellent techniques to diagnose and localize the lesions [3]. The serologic tests are of little practical value in confirming the diagnosis of cerebral echinococcal disease [2].
Surgery is the standard and most effective treatment for intracranial hydatid cysts. The preoperative diagnosis is very important both in planning the surgery and taking the measures against spillage of daughter cysts and scolices at surgery. Rupture is associated with the well-recognized problems of anaphylaxis, meningitis, or local recurrence from spillage of the cyst contents [3].
Nevertheless, hydatid cyst is a benign lesion, appropriate and timely diagnosis and management are mandatory for reducing mortality and morbidity [3,4].