Added value of 3D-DRIVE and SWI Magnetic Resonance Imaging Sequences in Intraventricular Neurocysticercosis (IVNCC): An Institutional Experience from Northeast India

Background: Prompt diagnosis and early treatment institution are important in intraventricular neurocysticercosis (IVNCC) as compared to the parenchymal or racemose form because it is associated with a poorer patient prognosis. Intraventricular neurocysticercosis is often missed on CT scan or conventional cranial magnetic resonance imaging because of similar density or signal intensity of cysticercus lesion with cerebrospinal fluid.Thestudy aims to evaluate the added value of 3D-DRIVE and SWI MRI sequences in isolated intraventricular cysticercosis with acute neurological presentation. Methods and Materials: This retrospective study was carried out on diagnosed 10 patients with isolated intraventricular neurocysticercosis (IVNCC) presented to a tertiary care hospital with an acute onset of symptoms or acute neurological deficit between June 2019 to May 2021. Relevant neurological examination, CSF analysis, a serological test of neurocysticercosis and MRI scan of the brain were performed. Result: Tenpatients of isolated intraventricular neurocysticercosis (3 males and 7 females) having 3 pediatric and 7 adults were included in this study sample.The common neurological complications of the isolated intraventricular neurocysticercosis in this study are observed as obstructive hydrocephalus in 8(80%) patients and ependymitis in 7(70%) patients. IVNCC with distinctly visualized scolex (visibility score 2) identified in 2(20%) patients in T2WI, 8 (80%) patients in 3D-DRIVE and 3(30%) patients in SWI sequences. The cyst wall of IVNCC was distinctly visualized (visibility score 2) in 1(10%) patient in T2WI, 8(80%) patients in 3D-DRIVE and 6(60%) patients in SWI sequence. Conclusion: Heavily T2-weighted steady-state and SWI sequences should be added to routine MRI sequences that helps to identify IVNCC and should be used in patients with unexplained hydrocephalus, especially in endemic regions of Neurocysticercosis.

In intraventricular neurocysticercosis, the larvae of Taeniasolium reach the cerebral ventricles via the choroid plexus and causes symptoms from CSF flow obstruction toependymitis, ventriculitis, or both [1,2].
Most of the IVNCC is usually occult or missed on CT scan owing to attenuation characteristics of cysticercus cyst fluid equal to those of CSF. Neurocysticercus lesions in the CSF spaces are usually missed on conventional MRI sequences. Sometime post-gadolinium MRI images are not able to characterize the IVNCC because the signal intensity of the cyst is similar to that of CSF [8].
It has been shown that heavily T2-weighted high-resolution steady-state sequences like 3D-DRIVE/3D-CISS/FIESTA better delineates the cysticercus lesions in cisternal spaces, cerebral sulci or within the ventricle [9]. The 3D-DRIVE sequence is a 3D T2-weighted driven equilibrium radiofrequency reset pulse. CISS is a heavily T2W constructive interference in steady-state sequenceand FIESTA is a fast imaging employing steady-state acquisition.
These heavily T2-weighted images increase the conspicuity of the lesion within a CSF space. So it is able to identify the cyst wall or scolex, which are not otherwise seen on conventional MRI [10].
Susceptibility weighted imaging (SWI) sequence is a 3D gradient-echo sequence with both magnitude and phase information, it separately and in combination provides additional information in identifying the calcified scolex of intraventricular cysticercus lesion in comparison to the conventional MRI sequences [11,12].
Advanced MRI techniques can be able to identify the adherence of IVNCC into the wall of the ventricle or able to detect ventriculitis, ependymitis and obstructive hydrocephalus. Identification of adherent IVNCC is of utmost importancein MRI imaging, as even surgical resection sometimes fails to treat it, and in such situation it may need a CSF diversion with or without cyst excision [1,13].
Intraventricular Neurocysticercosis (IVNCC) had a poorer prognosis than other forms of Neurocysticercosis [14]. The active viable stage of Intraventricular Neurocysticercosis doesn't produce a reaction to the host, however, it may produce noncommunicating hydrocephalus.With the death of intraventricular larva, the host reaction is induced in the form of ependymitis, ventriculitis and meningoencephalitis.
The common alarming symptoms of IVNCC include acute onset of headache, vomiting, decreased visual acuity, altered mental status and even death [1,4,5]. Isolated intraventricular neurocysticercosis, especially in the fourth ventricle, can cause mechanical obstruction of CSF flow subsequently resulting in hydrocephalus [4,5]. The inflammatory process in IVNCC varies according to the location of the parasite [15]. MRI with newer advanced techniques is necessary to locate the IVNCC prior to surgery, as sometime IVNCC are mobile and migrated within the ventricular system.
The study aims to evaluate the added value of 3D-DRIVE and SWI MRI sequences in acute neurological complications of isolated intraventricular cysticercosis.

Methods and Materials
Patient selection: The case records of the 10 patients were retrospectively analyzed from June 2019 to May 2021. All patients of isolated intraventricular neurocysticercosis (IVNCC) presented with features of raised intracranial pressure with the onset of symptoms of headache, vomiting or acute neurological deficit. This retrospective study was approved by the institutional ethics review committee.
Inclusion criteria: 1. Only isolated intraventricular neurocysticercosis with acute clinical presentation.
Exclusion criteria: 1. Intraventricular neurocysticercosis along with a parenchymal or racemose form of neurocysticercosis.
MRI Protocol: All 10 patients underwent an MRI scan of the brain, using a 1.5 T MR scanner, Philips Ingenia (Philips Medical System, The Netherlands). MRI scans of the brain was done using a dedicated 32 channel head coil. Conventional MRI sequences include axial T1WI, T2WI, FLAIR (fluid-attenuated inversion recovery), DWI (diffusion-weighted imaging), sagittal T1WI and coronal T2WI. 3D-DRIVE (3D T2-weighted driven equilibrium radiofrequency reset pulse) and SWI (susceptibility-weighted imaging) sequences were obtained, followed by post-gadolinium T1WI sequences in all three planes. The parameters of the various MRI sequences used are shown in Table 1. .V. Gadolinium 1ml/kg bodyweight MRIEvaluation: MRI images were evaluated for the location and size of the intraventricular neurocysticercosis. The presence of a scolex was looked for in the T1WI, T2WI, 3D-DRIVE and SWI images. Presence of cyst wall or wall calcification was also looked for in SWI and 3D-DRIVE sequences. The maximum wall thickness of the intraventricular cyst was measured in the 3D-DRIVE sequence. The pattern of post-contrast enhancement of the IVNCC, associated ependymitis, meningitis, hydrocephalus and entrapment of ventricle were also observed.

Visibility score of Intraventricular neurocysticercosis (IVNCC):
The visibility of the wall and scolex of the intraventricular neurocysticercosis was categorized on a 3-point scale from 0 to 2. Score 0 means "notdetected", 1 means "probablyseen" and 2 means "distinctlyseen". To know the diagnostic performance of T2W, 3D-DRIVE and SWI sequences in the detection of intraventricular neurocysticercosis, this visibility score was calculated.

Neurological assessment of intraventricular neurocysticercosis(IVNCC): The details of clinical and neurological examinations performed in all patients.
Follow up and final diagnosis: Craniotomy with microsurgical cyst excision was done in 2 patients and neuroendoscopic cyst excision in another 4 patients, and histopathological confirmation of cysticercus lesions were confirmed. Three patients were confirmed having IVNCC on subsequent follow up MRI scans on basis of regression in size or complete healing of cysticercus lesion, with initial positive IgM antibodies against cysticercus antigens measured by ELISA technique both in CSF and Serum serology. Another 1 patient was diagnosed with IVNCC only basis of initial MRI imaging findings of intraventricular cyst with positive IgM antibodies against cysticercus antigens both in CSF and Serum.
All 10 patients received anticysticercal therapy with albendazole. Patients were followed up for a period of 6 months to 18 months.
Statistical analysis: All statistical analysis was performed using Statistical Package for Social Science (SPSS, version 16). Data were presented in terms of percentage and mean. A Chi-square test is done to find out the sensitivity and specificity of T2W, 3D-DRIVE and SWI sequences.
Four (40%) patients were treated conservatively with cysticidal drugs only and 6 (60%) patients were treated surgically followed by cysticidal drugs. Craniotomy with micro-surgical resection was done in 2 patients with 4 th ventricular neurocysticercosis and endoscopic approach in another 4 patients with lateral and 3 rd ventricular neurocysticercosis. On follow-up, 8(80%) patients show complete healing of the intraventricular neurocysticercosis, 1 (10%) patient showed disease recurrence and another 1 (10%) patient died.

Discussion
Acute onset of headache, vomiting, altered mental status and visual disturbance can occur in intraventricular neurocysticercosis (IVNCC) [16]. Acute onset of hydrocephalus can lead to sudden death due to brain stem herniation, displacement or distortion [17]. This sudden onset of symptoms is associated with changes in patient's head position, because acute ventricular obstruction can occur in Bruns' syndrome [18,19]. It occurs due to intermittent CSF flow obstruction by the ball-valve movement of intraventricular cysts. Intraventricular neurocysticercosis occurs in approximately 20% of patients of neurocysticercosis worldwide [20]. It carries high mortality rate due to acute onset of hydrocephalus and neurological detoriation. The viable intraventricular neurocysticercosis is often freely mobile and may lodge in ventricular foramina like foramen of Monroe, Luschka, Magendie or aqueduct of Sylvius, and lead to acute obstructive hydrocephalus [21]. Isolated fourth IVNCC is associated with ependymitis, arachnoiditis and ventriculitis [21].
CT scan fails to identify IVNCC that do not deform the ventricle because of same density of cyst with CSF, cyst wall and scolex not visible or cyst wall not shows any abnormal wall enhancement [22,23,20,21]. MRI can able to identify IVNCC in approximately 80% of cases [24] with a classical intraventricular cyst with scolex [25].
MRI appearance of an intraventricular cystic lesion with T1-weighted hyperintense or T2-weighted hypointense scolex within are considered as pathognomonic for intraventricular neurocysticercosis and these characteristics are usually not detected by CT scan. Conventional MRI sequences routinely fails to identify the scolex or cyst wall. Hence additional newer advanced MRI sequences like 3D-DRIVE and SWI act as a solving tool in the identification and characterization of intraventricular cystic lesions [10].
The common differential diagnosis of intraventricular NCC included colloid cyst, ependymal cyst, choroidal plexus cyst, intraventricular epidermoid and arachnoid cyst. And to differentiate these intraventricular cystic lesions newer advanced MRI techniques are necessary [ Table 3]. The colloid cyst typically showed T1-weighted hyperintensities and was classically located in the anterior third ventricle or foramen of Monroe region. CT scan shows hyperdensity within the colloid cyst. Ependymal cyst is difficult to differentiate from an adherent intraventricular NCC, but ependymal cyst wouldn't show scolex. The common location of ependymal cyst is in the frontal horn of lateral ventricle, where the cystis located near tothe foramen of Monroe region causing obstructive hydrocephalus. The choroid plexus cyst is usually asymptomatic and confines in the posterior body of the lateral ventricle. Intraventricular epidermoid cyst showed typical diffusion restriction without any scolex. Intraventricular arachnoid cyst suppressed signals on FLAIR images with an absence of scolex.
IVNCC withoutabnormal post-contrast enhancement should be treated surgically with either neuroendoscopic or open surgery for cyst excision. Those IVNCC that showa peripheral rim-like post-contrast enhancement with or without adjacent ependymitis should probably undergo the CSF flow diversion with VP shunt or partial cyst excision with the CSF diversion. IVNCC showing rimlike post-contrast enhancement denotes ependymitis;if it is surgically resected, patient is likely to develop hydrocephalus after surgery.
The surgical treatment options for intraventricular NCC depend on the clinical presentation, location and stage of IVNCC. Usual endoscopic or open microsurgical removal of intraventricular NCC should be considered if there is a CSF obstruction or mass effect, or fourth ventricular cyst.
Various recent literatures show application of various newer MRI sequences for identification and localization of IVNCC [26,27]. Conventional MRI sequences are lesssensitive for identificationof IVNCC, however the previous study of Singh et al. [26] identified scolex on FLAIR and T1W images in 3 out of 4 patients of IVNCC, and T2W fails to identify the same. Govindappa SS et al. [10] found more accuracy of 3D-CISS than of conventional MRI sequences for identification of IVNCC. However, Robbani I et al. [28] and Mont' Alverne Filho FE et al. [9] found more accuracy of 3D-SPGR (spoiled gradient recalled echo) overthat of conventional MRI sequences for identification of IVNCC. Table 4 shows few review literature of intraventricular neurocysticercosis. Limitation: Due to exclusion of patients with presence of intraventricular NCC along with the parenchymal form of NCC as well as IVNCC with racemose form of cysticercosis, the sample is limited to only isolated IVNCC in our study, and the sample size decreases. Still we tried to findout the visibility scores of T2W, 3D-DRIVE and SWI sequences for detection of wall and scolex of intraven-tricular NCC. Therefore, a larger study sample size is needed to confirm these added values of various MRI sequences in diagnosis, detection of cyst wall and scolex in isolated intraventricular NCC.

Conclusion
Newer heavily T2-weighted MRI sequences (like 3D-DRIVE/FIESTA/CISS) and SWI improve the sensitivity of detection and localization of intraventricular neurocysticercosis, and further aid in guiding the management and neuroendoscopic cyst excision and further improvement of patients suffering from this disease. In a patient with an unexplained obstructive hydrocephalus especially from endemic regions of neurocysticercosis these newer MRI sequences may be added to conventional MRI sequences