Epileptogenic Cerebral Hydatid Cyst Masquerading as a Low-Grade Glioma: Importance of an Advanced MRI Pulse Sequence
Year: 2025
Type: article
Study design: Case Report
Abstract: Sir, Intracranial hydatid cyst often presents as a well-defined solitary, nonenhancing cystic lesion generally in the middle cerebral artery territory without surrounding edema or mass effect; however, they can cause significant mass effect and hydrocephalus.[1] Uncommonly intracranial hydatid cyst may present as a multicystic lesion, with associated mass effect and edema, that might leads to difficulty in distinguishing from similar-looking neoplastic lesions such as astrocytoma or infective lesions. We present a case of cerebral hydatid in a young patient who presented with a long history of seizure, and we will also discuss various MRI findings with the importance of advanced MRI sequences. A 19-year-old male patient presented to our hospital with a 4-year history of seizures since then he has been treated conservatively with antiepileptics medications. There was no history of trauma, fever, and focal neurological deficit. MRI brain was done with clinical suspicion of low-grade glioma and revealed a well-defined T1 hypo and T2 hyperintense lesion in the right parietal lobe in subcortical location. The lesion shows a double-layered rim on both T1 and T2 with no enhancement [Figures 1]. FLAIR images show signal suppression of the central part with peripheral hyperintense rim [Figure 2]. No significant surrounding edema, blood products, or calcification noted. The mass effect is minimal as compared to the size of the lesion. Heavily T2-weighted sequence (CISS – constructive interference in steady state) showed multiple well-defined internal cysts that were not visible on other sequences [Figure 3]. MRS from the center of the lesion showed a pyruvate peak at 2.3 ppm. The most interesting observation was the presence of multiple daughter cysts visible only on the CISS sequence, and we called it “Bubbly CISS Sign.” USG abdomen and chest X-ray were normal. Based on characteristic MRI findings and positive hydatid serology, the diagnosis of intracranial hydatid cyst was made.Figure 1: Axial T1-weighted image (a) shows a hypointense lesion with no enhancing component in right parietal lobe. Axial T2 image shows a well-defined hyperintense lesion in the right parietal lobe with some fine septations. No significant surrounding edema or mass effect on adjacent sulciFigure 2: Axial FLAIR images (a and b) show suppression of the central fluid signal. A peripheral hyperintense halo (a) is present. Multiple septations with a multilocular appearance (b) can be seen in the inferior and posterior aspect of the lesionFigure 3: Constructive interference is steady state (CISS) (heavily T2-weighted sequence) images. (a-c) show multiple daughter cysts (Bubbly CISS Sign). MRS (d) shows pyruvate peak at 2.3 ppmThe incidence of intracranial hydatid in India is around 0.2%.[2] Echinococcus granulosus, a tapeworm, is the causative organism and transmitted by the ingestion of food or milk contaminated by dog feces containing ova of the parasite or by direct contact with dogs. The occurrence of multiple cysts also reported in the literature, which occurred either spontaneously, after trauma, or postoperative complications.[1-3] They are slow-growing lesions, with a variable growth rate between 1.5 and 10 cm/year.[4,5] The patients usually present with features of raised intracranial pressure and focal neurological deficit; however, studies have documented seizure as a presenting complaint.[6] Intracranial hydatid cysts are classified as primary or secondary types depending on whether other organs have not/have involved. The supratentorial brain parenchyma is commonly affected; however, S Bhaskar et al. have reported the infratentorial cerebellar hydatid cyst.[6,7] Secondary hydatid cysts are more common and developed spontaneously or after seeding from the rupture of a primary cyst.[5] Skull vault, extradural space, intraventricular region, meningeal surface, and brainstem are the other intracranial involvements.[3] The cyst wall contains an outer chitinous layer and an inner germinal layer. The germinal layer may develop internal protrusions and eventually form daughter cysts within the original cyst. The majority are unilocular, CSF density (on CT), or intensity (on MRI) lesions with a thin fibrous wall, which on T2-weighted MRI appears as hypointense rim; this appearance is considered diagnostic. This peripheral T2/FLAIR hyperintense rim has been described in cerebral hydatid disease, as seen in our case. Both hypointense thin rim and T2/FLAIR hyperintense rim are equivalent to pericyst. Calcification is infrequent and reported in less than 1% of cases.[8] The CT shows calcification better than MRI. The cyst usually lies just a few millimeters below the cortex and can also protrude and adhere to the meninges, calvaria, and erode the vault. Surrounding bony sclerosis may be present as well at the periphery. DWI MRI shows increase diffusivity, while SWI images show no overt hemorrhage and calcification. The hydatid may show the presence of internal separations or internal smaller cysts knowns as daughter cysts. The presence of daughter cysts is considered pathognomonic.[7,9] Daughter cysts have similar imaging features as the mother cyst though they are less hyperintense on T2W MR. Edema and enhancement is not a feature of intracranial hydatid. When present, it indicates ongoing inflammation and cyst rupture. Such cases are challenging to differentiate from other cystic lesions that show peripheral enhancement with surrounding edemata such as abscesses, giant granulomas, giant neurocysticercosis (NCC), or cystic gliomas. CISS is a gradient echo MRI sequences. It has various intracranial applications such as visualization of cranial nerves, inner ear structures, scolex in NCC.[10] Our case showed its usefulness in showing daughter cysts, which conventional MRI sequences failed to demonstrate. MR spectroscopy (MRS) may help as a problem-solving tool in doubtful cases. Kohli et al. performed in vivo MRS in patients of intracranial hydatid cyst and found, besides the presence of lactate, alanine, and acetate metabolites, a considerable resonance for pyruvate at 2.3 ppm. The MRS pattern appeared different from the other cystic lesions of the brain, and they have suggested MRS as an adjunct to imaging in the differential diagnosis of intracranial hydatids.[11] Cerebral alveolar hydatid cyst is a rare type of hydatid cyst and caused by Echinococcus multilocularis. These lesions present as a firm masses full of connective tissue and produce perilesional edema, although they are well demarcated. The solid enhancing areas and calcification are also often present. We consider the possibility of giant NCC; however, in most cases, NCC is unilocular and shows the presence of scolex and does not show smaller internal cysts or septations. Besides, NCC also shows peripheral enhancement in colloid vesicular and granular nodular stage.[12-14] Other differential diagnoses include pyogenic abscess and cystic or necrotic tumors. Bacterial abscess shows marked rim enhancement, perilesional edema, and central restriction on diffusion-weighted MR images. Dysembryoplastic neuroepithelial tumor is a cystic tumor and is present with a history of seizure; however, it is a cortical-based lesion and is commonly involves the temporal lobe. Ganglioglioma is another cystic tumor present with a history of seizure; however, ganglioglioma shows mural enhancing nodule besides cystic lesion. Cystic granulomas, arachnoid cysts, epidermoid, and porencephalic cysts are other less common differentials. The previously believed more frequent presence of the unilocular nature of the cerebral hydatid cysts may not be valid with advanced imaging techniques like CISS, which may reveal the multilocular honeycomb appearance of daughter cysts, which we labeled as “Bubbly CISS sign,” which along with MRS may help in their diagnosis. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: Neurology India
Authors: Tameem Bhat, Pragya Chaturvedi, Shweta Jain, Neeraj Jain, Sunil Kumar
Language: English
Subfield: Pathology and Forensic Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
OpenAlex ID: W4409498315