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BJR Case Rep
Oxford University Press
bjrcr
BJR | Case Reports
2055-7159
Oxford University Press

38352260
10.1093/bjrcr/uaae001
uaae001
Case Review
Case collection: Imaging infections and infectious diseases
Bjr/Neuro
AcademicSubjects/MED00870
Racemose neurocysticercosis: a case series
Sharma Srishti MD Department of Radiodiagnosis, All India Institute of Medical Sciences, Patna 801507, India

Singh Anuradha MD Department of Radiodiagnosis, SGPGIMS, Lucknow 226014, India

Mani Vinita Elizabeth DM Department of Neurology, SGPGIMS, Lucknow 226014, India

Mishra Sarvesh Chandra MD Department of Radiodiagnosis, SGPGIMS, Lucknow 226014, India

Chaturvedi Pragya MD Department of Radiodiagnosis, SGPGIMS, Lucknow 226014, India

Jain Shweta MD Department of Pathology, SGPGIMS, Lucknow 226014, India

Kumar Sunil MD Department of Radiology, Medanta Super Speciality Hospital, Lucknow 226030, India

https://orcid.org/0000-0002-7502-9751
Jain Neeraj DMRD, DNB Department of Radiodiagnosis, SGPGIMS, Lucknow 226014, India

Corresponding author: Neeraj Jain, DMRD, DNB, Department of Radiodiagnosis, SGPGIMS, Raebareli Road,  Lucknow 226014, India (neerajdmrd@gmail.com)
1 2024
19 1 2024
19 1 2024
10 1 uaae00102 6 2023
20 9 2023
13 1 2024
11 2 2024
© The Author(s) 2024. Published by Oxford University Press on behalf of the British Institute of Radiology.
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

Abstract

Neurocysticercosis (NCC) is a common parasitic condition of the central nervous system in certain parts of the world. The racemose variety of NCC is distinct from the commonly seen parenchymal form. It frequently infiltrates the basal cisterns and Sylvian fissures. Imaging plays a vital role in the diagnosis; however, as their signal intensity is similar to cerebrospinal fluid and due to the absence of enhancement in most cases, imaging diagnosis is often difficult on the conventional MRI sequences. Here, we present five cases of racemose NCC to emphasize the importance of a heavily T2-weighted sequence (Fast Imaging Employing Steady-state Acquisition) sequence in the diagnosing this entity.

neurocysticercosis
racemose NCC
FIESTA
MRI
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pmcIntroduction

Neurocysticercosis (NCC) is a common parasitic infection affecting the central nervous system (CNS) and constitutes a public health challenge for most developing countries.1 It is caused by the larval form of the pork tapeworm Taenia solium. Depending on the site of involvement, they are classified into intraparenchymal, extra parenchymal (subarachnoid-cisternal, meningeal, intraventricular) and mixed types.2 Among these, parenchymal involvement is the most common. As with other haematogenously transmitted diseases, it typically involves the grey-white matter junction, as parasites often lodge here due to the smaller calibre blood vessels.3 If larvae lodge in the meninges or choroid plexus, the infection may involve the ventricular system and subarachnoid space. The subarachnoid or racemose NCC are frequently large-sized lesions as the subarachnoid space provides ample space to grow compared to the parenchymal variety. Furthermore, unlike parenchymal NCC, racemose NCC clinical presentation is variable, making their diagnosis extremely challenging.

MRI plays a crucial role in the diagnosis; however, considering that the signal intensity of the lesion is similar to cerebrospinal fluid (CSF) signal intensity on all conventional sequences and the lack of enhancement in most cases makes their prospective diagnosis quite tricky. Herein, we present a case series depicting the MRI findings of racemose NCC. We emphasize the importance of a heavily T2-weighted sequence (FIESTA—Fast Imaging Employing Steady-state Acquisition) in their diagnosis (Table 1).

Table 1. The demographics, clinical manifestations, and MRI findings of these cases.

Patient	Age/gender	Type and duration of symptoms	Lesion location	Internal septations (on FIESTA)	Scolex	Enhancement	
1	52 years/F	Fever, headache, and vomiting—2 months	Prepontine cistern and the cisternal spaces along the midbrain	Present	Absent	None	
2	10 years/M	Headache and seizures—2 months	Pineal region	Present	Absent	Yes	
3	37 years/M	Headache and seizures—2 months	Under surface of the corpus callosum, roof of the third ventricle and basal cisterns	Present	Absent	Absent	
4	56 years/M	Seizure disorder and slowness of gait—5 years	Ambient cistern and Sylvian fissures	Present	Absent	Absent	
5	61 years/M	Headache and fever—2 days	Sylvian fissure	Present	Present	Present	

Case 1

A 52-year-old female patient presented with a history of fever, headache, and vomiting for 2 months. Based on her symptoms and background, an initial diagnosis of CNS tuberculosis (TB) was suspected. Subsequently, a gene expert test for TB was negative, and CSF analysis revealed normal protein, sugar, and lactate levels.

T2-weighted MRI imaging (T2WI) of the brain showed expansion of the left prepontine cistern with the subtle presence of fluid-signal intensity cystic lesions, which extended posterior to the midbrain and displaced it towards the contralateral side (Figure 1A and B). Moderate hydrocephalus was also noted. The lesions were better delineated on FIESTA images with thin septations as additional findings; these septations were not seen on T2 (Figure 1C and D). No scolex was identified, and there was no post-contrast enhancement. Based on imaging findings, a diagnosis of racemose NCC was made. The patient was put on conservative medications and is currently on follow-up.

Figure 1. Axial T2-weighted images showing a CSF signal intensity cystic lesion in the prepontine cistern (A) and in the cisternal space along the midbrain (B). Axial FIESTA—Fast Imaging Employing Steady-state Acquisition images (C, D) aid better visualization of the lesions with thin internal septations.

Case 2

A 10-year-old boy presented to our hospital with a history of frequent headaches and seizures for 3 months and visual disturbances for 4 days. MRI brain revealed a multiloculated cystic lesion in the pineal region extending into the third ventricle with resultant obstruction (Figure 2). It was hypointense on T1 (Figure 2A) with a thin rim of peripheral enhancement on the post-contrast study (Figure 2B). T2 and FIESTA images showed a characteristic multiloculated appearance (Figure 2C and D), classically called a “cluster of grapes” appearance. The lesion caused a mass effect on the tectum and thalami with the narrowing of the aqueduct of Sylvius.

Figure 2. Axial T1-weighted image (A) showing a multiloculated cystic lesion in the pineal region with peripheral enhancement on the post-contrast sagittal image. (B) Axial T2 and FIESTA—Fast Imaging Employing Steady-state Acquisition images show a multiloculated cystic lesion in the pineal region (arrow).

Case 3

A 37-year-old male patient has a history of frequent headaches and recurrent seizures for 2 months. MRI revealed dilatation of the extra-axial CSF spaces with septations along the inferior aspect of the corpus callosum. The third ventricle roof was displaced posteriorly into the basal cisterns (Figure 3A and B). Moderate non-communicating hydrocephalus was also noted with the normal-sized fourth ventricle. The FIESTA sequence could depict the multiseptated nature of the lesion more clearly. Contrast enhancement and diffusion restriction were absent. The patient improved on conservative management and is currently on follow-up.

Figure 3. Axial T2-weighted image (A) shows a multiloculated cystic lesion along the roof of the third ventricle with further extension along the undersurface of the corpus callosum. The axial FIESTA—Fast Imaging Employing Steady-state Acquisition (B) image shows a better definition with thin internal septations.

Case 4

A 56-year-old male patient came to our hospital with a history of seizures, gait impairment, incontinence, ataxia, and forgetfulness for 5 years. Based on the presence of hydrocephalus on the previous MRI, he was treated elsewhere on the line for CNS tuberculosis. However, despite 3 months of antitubercular treatment, he showed no signs of improvement.

A repeat MRI was done to look for an alternate diagnosis. It showed a dilated ambient cistern with indentation on the pons (Figure 4A). The lateral ventricles were markedly dilated along with dilatation of bilateral CSF spaces in the temporoparietal region with dominant involvement of Sylvian fissures (Figure 4B). On FIESTA MRI (Figure 4C and D), the lesion showed thin septations in the ambient cistern and Sylvian fissures, which strongly suggested the diagnosis of racemose NCC. Moderate hydrocephalus was also present. The patient was advised for VP shunt placement and is currently on follow-up.

Figure 4. Axial T2-weighted image (A) shows dilated ambient cistern with an indentation on the pons. Axial T2 image (B) shows dilated lateral ventricles with widened sulcal spaces in the temporoparietal region. Axial FIESTA—Fast Imaging Employing Steady-state Acquisition image (C) revealed a cystic lesion in the ambient cistern, causing indentation on the pons. In addition to the widening of sulcal spaces, the axial FIESTA—Fast Imaging Employing Steady-state Acquisition image (D) shows thin septations.

Case 5

A 61-year-old male complaining of headaches for 3 days and fever for 2 days came to our outpatient department. He had a history of a right middle cerebral artery territory infarct in January 2020. Clinical examination was unremarkable except for a poor swallowing reflex. On T2W MRI, a hyperintense multilobulated cystic lesion was detected in the right Sylvian fissure (Figure 5A and B). It showed smooth peripheral enhancement (Figure 5C). Eccentric blooming focus representing scolex was seen on susceptibility-weighted imaging (SWI, Figure 5D). Scolex represent armed rostellum and body of cysticercus, as larvae progress through different stages scolex undergoes sequential changes and finally becomes calcified in calcified nodular stage. In addition to showing cystic lesions, the FIESTA image showed multiple thin septations in the rest of the Sylvian fissure, suggesting a more extensive involvement (Figure 5D and E). Based on imaging findings, a diagnosis of racemose NCC was suspected. He showed improvement on conservative treatment and presently is on follow-up.

Figure 5. Axial T2-weighted images show a cystic lesion in the right Sylvian fissure (A) with asymmetric prominence of the right Sylvian fissure (B). Axial T1 image (C) showing smooth peripheral enhancement. The susceptibility-weighted image (D) shows a blooming focus in the cystic lesion, representing a scolex. Axial FIESTA—Fast Imaging Employing Steady-state Acquisition (E, F) images better visualize the cystic lesion and additionally demonstrate multiple thin septations in the widened right Sylvian fissure.

Discussion

Cysticercosis is considered one of the common helminthic infections of the brain and a leading cause of acquired epilepsy worldwide.4 Clinical manifestations of NCC are highly variable, with seizures being the most common presentation mode. There may be focal neurological deficits, intracranial hypertension, or cognitive decline. The onset of symptoms after the initial infection is variable, and it depends on the cysts’ number, size, location, and the host's immune response to the parasite.5

While the brain parenchyma is often considered the most common location for NCC, a few studies suggest that the subarachnoid-cisternal location may be more prevalent.6–9 These studies argue that parasites' “parenchymal” location, as described in cross-sectional imaging, may represent subarachnoid cysticercosis located in deep sulci or in perforating branches of perivascular spaces.10 Nonetheless, the distinction between parenchymal and extraparenchymal location has significant clinical and prognostic implications. The parenchymal forms behave differently clinically and are more responsive to anthelminthic medications than the subarachnoid forms.

Escobar classified the parenchymal NCC into four pathological stages: vesicular, colloidal vesicular, granular nodular, and calcified nodular.11 Imaging findings and clinical presentation at each stage reflect underlying changes in the disease process and host response.12 Patient presentation ranges from asymptomatic to encephalitis, depending on the disease stage.3,13–15 The importance of calcified granulomas with perilesional oedema as foci of seizures and epilepsy in populations where cysticercosis is endemic is newly recognized. It indicates that treatment with anti-inflammatory agents could control or prevent epilepsy in these patients.16

Conversely, racemose NCC develops due to the segmentation of cysticercosis cellulosae with the budding of new cysts in clusters. These cysts grow slowly and expand in CSF spaces such as ambient cistern, quadrigeminal cistern, and Sylvian fissure. They are significantly larger than the parenchymal forms owing to the ample availability of the CSF spaces (Figures 1-5). They lack the usual evolutionary stages of the parenchymal NCC. Scolex, which represents rostellum and body of a larvae, degenerates as cysts progress and finally becomes calcified in the calcified nodular stage. A scolex is considered as a hallmark feature of parenchymal NCC and is frequently absent in racemose NCC as it degenerates.17 Additionally, calcification, which is seen in the later stages of parenchymal NCC, and peripheral enhancement in vesicular and colloid vesicular stages of parenchymal NCC are also not seen in racemose NCC. However, sometimes, the racemose NCC can incite inflammation of surrounding tissues and may show enhancement (Figures 2 and 5). This inflammatory response can also cause vasculitis of the basal perforators, leading to infarcts.18,19

On conventional MRI, these lesions appear isointense to the CSF on all pulse sequences. Occasionally, they may show hyperintense signal on T1WI and FLAIR compared to the CSF due to their protein content.

When the ventricular system is involved, these cysts are frequently mobile and can cause acute obstructive hydrocephalus. Usually, they migrate from the lateral ventricle to the third ventricle and the fourth ventricle through the sylvius aqueduct.20 It often manifests as a solitary intraventricular cyst, the fourth ventricle being the most common location. The cyst wall may occasionally be seen as a thin linear structure on T2-weighted imaging or demonstrate contrast enhancement. They can cause ventricular deformity, enlargement, and hydrocephalus.

Serological tests (enzyme-linked immunoelectrotransfer blot assay, enzyme-linked immunosorbent assay) that detect anticysticercal antibodies in serum or CSF inherently lack specificity or sensitivity, thereby precluding their reliability in isolation.6 MRI is the primary diagnostic modality used for the detection of cysticercus lesions and their secondary complications.

A racemose NCC is more challenging to diagnose than a parenchymal NCC. These lesions are often missed on routine MRI of the brain owing to their signal, which is isointense to CSF and absence of contrast enhancement of the cyst wall.21 In the absence of a high index of suspicion, these lesions can be simply dismissed as communicating hydrocephalus (if intraventricular) or mistaken for other extraaxial cystic lesions (arachnoid cysts, epidermoid cysts, etc.) owing to their multicystic appearance.7,8 Hence, diagnosing an NCC, especially the racemose variant, is a multidisciplinary approach that involves the correct interpretation of the symptomatology, neuroimaging, and serology in the proper epidemiological context.

Fast Imaging Employing Steady-state Acquisition is a heavily 3D T2WI high-resolution gradient-echo sequence routinely used to evaluate the inner and middle ear's structures and cerebellopontine angle lesions. In this sequence, the residual transverse magnetization is refocussed to achieve a steady magnitude of transverse and longitudinal magnetization following a few repetition times (TRs). It significantly increases the conspicuity of lesions in cisterns, sulci, and intraventricular spaces. The millimetre-thin sections, short TE (limited signal loss resulting from magnetic susceptibility effects), and low flip angle (limited T1WI) allow superb spatial resolution and signal-to-noise ratio within a clinically feasible acquisition time.22 CISS (constructive interference in steady state) and DRIVE (Driven Equilibrium Radio Frequency Reset Pulse) are similar sequences used by other MRI manufactures.

As opposed to the T2W sequence, tissue contrast in FIESTA sequences is determined by the T2/T1 ratio of the tissues. It accentuates the contrast between the CSF and the surrounding structures, including the lesion. In comparison with conventional FLAIR or T2 sequences, this sequence is significantly better at detecting NCC lesions in intraventricular and extraventricular CSF spaces by allowing better visualization of the cyst wall, internal septations, and internal scolex.23

As previously discussed, scolex is frequently absent in racemose NCC. However, anecdotal case reports have described the presence of scolex on SWI sequences. This case series also shows the presence of scolex in one patient.21

The clinical presentation of racemose cysts is pleomorphic and quite different from parenchymal cysticercosis. Studies suggest that classification of the racemose NCC into meningeal, intraventricular, and cisternal forms can help us predict the clinical progression in these patients.10 The meningeal form refers to cases where the lesions are typically seen in the cerebral convexities. This form of racemose NCC results in raised intracranial pressure by causing meningitis and adhesions. It can also present with focal neurological deficit due to entrapment of the cranial nerves in the inflammatory exudate.14 The intraventricular form refers to cysticercus within the ventricular system. The cisternal form refers to racemose lesions within the basal cisterns. These forms can occlude the CSF pathway causing acute episodes of ventriculomegaly and a mass effect. They can also cause hydrocephalous as a sequalae of ependymitis resulting from the death of larvae.24 The blockage of CSF pathways resulting in raised intracranial tension and hydrocephalous is an important determinant in the prognosis of these patients. We propose the following imaging-based classification system to help prognosticate these patients and decide the management.

Type 1A—Meningeal form without hydrocephalous.

Type 1B—Meningeal form with hydrocephalous.

Type 2A—Intraventricular form without hydrocephalous

Type 2B—Intraventricular form with hydrocephalous.

Type 3A—Cisternal form without hydrocephalous.

Type 3B—Cisternal form with hydrocephalous.

Type 4A—Present in more than 1 location without hydrocephalous

Type 4B—Present in more than 1 location with hydrocephalous

The suffix + P to be used in the presence of associated parenchymal NCC.

The common differential diagnosis for subarachnoid NCC includes arachnoid cysts, neuroglial cysts, and epidermoid tumours. Like NCC, arachnoid cysts are located in the subarachnoid space. However, they are unilocular and devoid of septations and scolex. The neuroglial cyst can be intra- or intraparenchymal, with the former being more common. Like an arachnoid cyst, they lack septations. Ruptured hydatid cysts can also be a differential for racemose NCC, especially in areas with an endemic population. However, as hydatid cysts are primarily intraparenchymal before rupture, there may be some tell-tale evidence of their intraparenchymal location before they rupture into extraaxial CSF spaces. Moreover, positive hydatid serology will further be supporting evidence.7,8 However, for the detection of all of these cystic lesions in the CSF space, the FIESTA sequence is quite promising since it provides excellent contrast between the lesions and the CSF space.

Conclusion

Racemose NCC should be considered in the differential diagnosis of multiloculated, clustered cystic lesions involving extraaxial CSF spaces.

We recommend routine inclusion of the FIESTA sequence in the evaluation of cases of obstructive hydrocephalus or any cystic lesion involving the extraaxial CSF spaces in an endemic region. Not only can this sequence demonstrate septations within the lesion as involving the subarachnoid spaces, but it may also help in identification of the cyst in an intraventricular location that otherwise remains occult on other MRI sequences.

Learning points

Racemose NCC is distinct from parenchymal variant. It infiltrates CSF spaces like basal cistern, Sylvian fissure, and around brain stem.

It often lacks scolex and does not show enhancement.

It should be considered in the differential diagnosis of multiloculated cystic lesions in extraaxial CSF spaces

A heavily 3D T2WI high-resolution gradient-echo sequence accentuates the contrast between the CSF and the surrounding structures, thereby improving lesion visibility.

Funding

None declared.

Conflicts of interest

None declared

Informed consent statement

Written informed consent was obtained from the patients for publication of this case report, including accompanying images.
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