Echinococcosis is a zoonotic disease caused by the larva of tapeworm Echinococcus. All four species of echinococcus documented in the literature are involved in the etiology of human infection namely—Echinococcus granulosus (cystic hydatid disease), Echinococcus multilocularis (alveolar hydatid disease), Echinococcus vogeli, and Echinococcus oligarthus . In their reproductive cycle, humans are an accidental intermediate host. Liver (59–75%) is the most common site involved. This is followed by lung (27%), kidney (3%), bone (1–4%), and brain (1–2%) which is a least affected organ. Various distant unusual anatomic locations like the heart, spleen, pancreas, ovaries, parametrium, pelvis, omentum, thyroid, orbit or retroperitoneum, and muscles are also seen to be involved . Definitive hosts are the carnivores, such as dogs or wolves where the adult worms inhabit in the proximal small intestine attached by the hooklets to the mucosa; whereas intermediate hosts are the herbivores such as sheep, cattle and goats housing cyst stage of the worm. Eggs of an adult tapeworm are passed in infected dog feces that is ingested by sheep while grazing. These cysts hatches into embryos in the intestine and penetrate the intestinal mucosal lining reaching the portal circulation. The embryos after reaching the host organ transform into larval echinococcal cysts in which numerous tapeworm heads (called protoscoleces) are produced via asexual reproduction. When dogs ingest the viscera containing echinococcal cysts the life cycle is completed. Humans are accidental intermediate hosts in the tapeworm life cycle . Primary multiple hydatid cysts of the brain are extremely rare. Intra-cranial hydatid cysts do not show symptoms till they attain a large size. Large cerebral hydatid cysts interfere with the cerebrospinal fluid flow resulting in obstructive hydrocephalus. Headache and vomiting are the most common symptoms, whereas motor weakness and seizures can also be seen . Computed tomography and magnetic resonance imaging shows well-defined smooth thin-walled spherical/oval cystic lesions with cystic component of fluid attenuation .
On MRI, T1-weighted and T2-weighted images show low signal intensity cyst wall. Wall calcification is rare and reported to be in < 1% of all cases. Cerebral abscesses and cystic tumors usually show surrounding oedema and peripheral rim enhancement. It is not seen in untreated or uncomplicated cases of cerebral hydatid cyst irrespective of mass effect . Magnetic resonance spectroscopy and diffusion weighted imaging are used to distinguish cerebral hydatid cysts from cerebral abscesses, necrotic brain tumors including cystic lesions . Generally, acetate and succinate metabolic end products are known for arising from microorganisms .
But, metabolic end products for hydatid cysts are non-specific and are similar as in case of abscesses and neurocysticercoses . Here, in our case the magnetic resonance spectroscopy of fluid filled cystic part of lesion shows elevated choline/NAA ratio with elevated choline and pyruvate levels and the peripheral solid part shows peak of lipids.
Intra-operative cyst rupture may occur in 28% of the cases. If it ruptures into subarachnoid space of the brain, it can cause severe anaphylactic reactions. Usually, albendazole is given in cases of recurrence, intraoperative rupture of the cysts, inoperable cases with widespread disease and is recommended before operation for intracranial tension reduction [12, 13].