Introduction
Neurocysticercosis remains the most common parasitic infection of the central nervous system worldwide. Intraventricular neurocysticercosis (IVNCC) represents roughly 10–20% of cases and is one of the most dangerous phenotypes because obstruction may occur abruptly, intermittently and sometimes catastrophically (White et al., Reference White, Coyle, Rajshekhar, Singh, Hauser, Mohanty, Garcia and Nash2018; Takayanagui and Haidar, Reference Takayanagui and Haidar2022). Fourth ventricular involvement is the most frequent intraventricular location, followed by the third and lateral ventricles (Nash et al., Reference Nash, Ware and Mahanty2018; Mendieta-Barrera et al., Reference Mendieta-Barrera, Punukollu, Rios-hurtado, De Nigris Vasconcellos, Garcia-Torrico, Salolin-Vargas, Mamani-Julian, Valderrama, Rivera-Hurtado, Ballesteros-Herrera, Tripathi, Torres-Corzo and Ghaffari-Rafi2025).
Unlike many parenchymal and intraventricular lesions, a viable intraventricular cyst may remain non-adherent and behave as a mobile intraluminal body. This mobility explains why some patients present with episodic obstruction, transient hydrocephalus or Brun syndrome, a ball-valve phenomenon classically characterized by sudden headache, vomiting, vertigo and gait instability precipitated by head movement (Torres-Corzo et al., Reference Torres-Corzo, Rodriguez-della Vecchia and Rangel-Castilla2006; Shahani et al., Reference Shahani, Garnes and Mejia2015; Nash et al., Reference Nash, Ware and Mahanty2018; Baro et al., Reference Baro, Anglani, Martinolli, Landi, D’avella and Denaro2020; Chugh et al., Reference Chugh, Gotecha, Punia, Raghu, Patil and Kotecha2021). Migration documented on sequential neuroimaging is also recognized as a confirmatory neuroimaging feature in contemporary diagnostic criteria for neurocysticercosis (Del Brutto et al., Reference Del Brutto, Nash, White, Rajshekhar, Wilkins, Singh, Vasquez, Salgado, Gilman and Garcia2017).
Most discussions of IVNCC emphasize diagnosis and removal, but less attention has been paid to the mechanics and consequences of the wandering cyst. That gap matters clinically: once a cyst can migrate, it can change the obstructive point, alter the surgical corridor and make the anatomy shown on earlier imaging unreliable. An illustrative case of migrating IVNCC is presented together with a focused case-based review of published migrating ventricular cysts. The aim was not to estimate the incidence of migration after cerebrospinal fluid (CSF) diversion or to assign a single causal trigger to every event, but to clarify how mobile cysts behave during acute hydrocephalus, posture changes and CSF pressure perturbation, and to distil practical lessons for surgical planning.
Materials and methods
This study combines an illustrative case report with a focused migration-oriented review of the literature. Case data were obtained from the treating neurosurgical service and were reviewed chronologically using clinical records, serial neuroimaging, operative details and post-operative evolution. After peer review, additional outside-hospital imaging was obtained and reviewed with neuroradiological input. This modified the interpretation of the temporal relationship between cyst migration and external ventricular drainage (EVD) placement: the image sequence documented active cyst relocation during the acute hydrocephalus-CSF diversion interval but did not allow the exact initiating trigger to be assigned.
The original search was performed in PubMed/MEDLINE and supplemented with Embase and the Cochrane Library using terms related to neurocysticercosis, migration, mobility, wandering cysts, ventricular or adjacent CSF spaces, Brun syndrome, EVD, shunt and endoscopy. The review was intentionally designed as a narrative, descriptive case-based synthesis rather than a registered systematic review or meta-analysis, because the aim was to contextualize a rare migratory event and its practical imaging implications rather than to compare interventions or estimate procedural risk.
Reports were included in the pooled migration analysis when they described lesion relocation documented radiologically, inferred intraoperatively or strongly linked to abrupt change in ventricular target localization. Reports that described IVNCC, Brun syndrome, endoscopic outcomes or diagnostic workflows without extractable individual migration events were retained for contextual discussion but were not included in the pooled migration counts. Twenty-three reports were retained for migration-oriented pooled extraction. After reconciliation of probable overlapping institutional case descriptions, these reports yielded 29 unique published migration events with sufficient detail for pooled coding.
Migration events were classified as intervention-associated when they followed an intervention expected to alter CSF pressure gradients or ventricular hydrodynamics, including ventriculostomy, shunting, lumbar puncture, pneumoencephalography or intraoperative/endoscopic irrigation-manipulation. Events were classified as positional when they were clearly posture-dependent, spontaneous when no intervention or positional trigger was evident and unknown when the report described relocation without enough detail for a more confident attribution. Potentially overlapping reports were cross-checked by age, ventricular location, trigger, migration pathway and operative course so that only unique events were counted once.
Because the source literature consists mainly of case reports and small case series, the pooled proportions were treated strictly as descriptive counts within a selected published sample. They were not interpreted as epidemiological risk estimates and were not used to infer procedure-specific causality. The present case was not added to the intervention-associated or spontaneous published-case numerator. After review of the additional images – including a CT from April 2024 that showed interval displacement before any intervention – the case was classified as spontaneous-onset migration with peri-decompression progression/indeterminate. This classification acknowledges the documented spontaneous movement prior to CSF diversion, while also recognizing that the acute-phase sequence did not allow the exact role of pressure-related changes during the EVD period to be determined.
Results
Illustrative case
A 50-year-old woman with neurocysticercosis was followed by a neuroinfectious diseases team after control magnetic resonance imaging (MRI) demonstrated an intraventricular cystic lesion in 2011. In 2023, she was later referred to the Hydrodynamics Unit of the University of Sao Paulo Clinics Hospital after the worsening of ataxia symptoms. At presentation to Neurosurgery, she had epilepsy, an ataxic syndrome and cognitive complaints. MRI dated 10 January 2023 showed a cystic lesion in the body of the left lateral ventricle, and endoscopic excision was recommended. She performed a CT scan dated 30 April 2024, which first showed a subtle migration of the cyst that was initially unnoticed during outpatient follow-up (Figure 1A,B).
Initial location and earliest evidence of interval migration. MRI in 2023 (A) showed the cystic lesion in the body of the left lateral ventricle. CT in 2024 (B) was retrospectively identified as the first study suggesting migration from the original lateral ventricular position, a change that had not been recognized at the time.
Figure 1 Long description
Composite neuroimaging figure comparing the initial and earliest migrated positions. Panel A contains sagittal MRI sequences from January 2023 showing a cystic lesion in the body of the left lateral ventricle. Panel B contains axial CT images from April 2024. Retrospective comparison with the earlier MRI shows subtle displacement from the original lateral ventricular position, representing the first recognized evidence of interval migration.
Definitive surgery was temporarily deferred because adult neuroendoscopic equipment was unavailable at the treating service. She remained under outpatient follow-up with relative symptomatic stability until August 2025, when she developed sudden severe headache, nausea, vomiting and decreased level of consciousness. At an outside emergency hospital, she was diagnosed with acute hydrocephalus and underwent urgent EVD placement on 14 August 2025. Her neurological status improved, the drain was eventually removed after successful weaning, and she was discharged without a permanent shunt.
Initially, detailed interval imaging from that acute admission had not been available for review. After contacting an external radiology team, the outside-hospital image set was obtained. Review of these images with neuroradiological input suggested that the cyst had already begun to leave its original lateral ventricular location by the time of the acute hydrocephalic episode. Acute CT on 14 August 2025 confirmed obstructive hydrocephalus, with the cyst almost reaching the third ventricle. CT on 15 August 2025 showed the lesion at the foramen of Monro, partly related to the left lateral ventricle and the third ventricle, and imaging on 16 August 2025 was interpreted as consistent with further caudal progression (Figure 2). This sequence documents active peri-decompression migration during the acute hydrocephalus-EVD interval. Critically, retrospective review of a CT scan from April 2024 – obtained 16 months before the acute episode – showed that the cyst had already begun to leave its original lateral ventricular location before any CSF diversion or surgical intervention. This indicates that the migratory process had a spontaneous component that predated the acute decompressive event. However, the sequence during August 2025 does not establish whether the caudal progression was purely a continuation of this spontaneous movement or was modified by the pressure changes surrounding EVD placement. The clinically relevant point is that the cyst location changed during the critical interval between rescue treatment and definitive surgery.
Acute peri-decompression migration. Pre-EVD CT on 14 August 2025 (A) showed acute obstructive hydrocephalus and the cyst passing through the foramen of Monro. First post-EVD CT on 15 August 2025 (B) showed the cyst still crossing the foramen of Monro, partly related to the left lateral ventricle and third ventricle. CT on 16 August 2025 (C), the second post-operative day, showed completion of caudal migration, with the cyst located inferior to the foramen magnum. Together, these images document active migration during the acute hydrocephalus–decompression interval but do not assign a single causal trigger.
Figure 2 Long description
Composite CT figure documenting active migration during the acute hydrocephalus and decompression interval. Panel A shows pre-drain CT on 14 August 2025 with acute obstructive hydrocephalus and the cyst approaching or passing through the foramen of Monro. Panel B shows the first post-drain CT on 15 August, with the cyst at the foramen of Monro, partly related to the left lateral and third ventricles. Panel C shows CT on 16 August with further caudal progression toward the foramen magnum region. The sequence documents changing anatomy but does not assign a single causal trigger.
When she returned to our institution in November 2025, she had worsened gait, required support to ambulate and reported memory lapses. Outside hospital MRI dated 29 August 2025 and follow-up MRI dated 22 October 2025 no longer showed the original left lateral ventricular lesion. Instead, a cystic lesion with the same morphology and signal characteristics was seen at the foramen magnum region, in continuity with the caudal fourth ventricular outlet. Given the disappearance of the original lesion, the acute-phase evidence of transition at the foramen of Monro/third ventricle and the later appearance of an indistinguishable cyst in a caudal CSF space, the most plausible interpretation was transventricular migration through the foramen of Monro, third ventricle, aqueduct, fourth ventricle and fourth ventricular outlet (Figure 3).
Persistent caudal location after the acute episode. MRI on 29 August 2025 was the first MRI to show the cyst below the foramen magnum. Follow-up MRI in October 2025 showed persistence of the cyst in the same location, with obstruction of cerebrospinal fluid flow at the foramen magnum, defining the final posterior fossa surgical target.
Figure 3 Long description
Composite MRI figure comparing follow-up studies after the acute episode. The 29 August 2025 examination first demonstrates the cyst in the foramen magnum region, in continuity with the caudal fourth ventricular outlet. MRI on 22 October 2025 shows the lesion remaining in the same position, with persistent obstruction of cerebrospinal fluid flow. The stable caudal location defined the posterior fossa surgical target.
In January 2026, she underwent midline suboccipital craniotomy in the Concorde position for definitive removal. Shortly after dural opening, the cyst extruded spontaneously under pressure (Video 1, Figure 4). Although cyst rupture could not be completely avoided, the capsule was fully removed and brisk CSF egress was observed, suggesting restoration of the natural pathways. She was extubated in the operating room, transferred to the intensive care unit, stepped down to the ward on post-operative day 2 and discharged home on post-operative day 6. A post-operative CSF leak through the subgaleal drain resolved with conservative management over the following days. Her headache improved after surgery.
Post-operative views from the suboccipital approach demonstrating cyst extrusion/removal and decompression of the CSF pathways.
Figure 4 Long description
A group of postoperative or operative views from the midline suboccipital approach demonstrates extrusion and removal of the neurocysticercal cyst and decompression of the cerebrospinal fluid pathways at the foramen magnum region.
Pooled review findings
The pooled review identified 29 unique published migration events across 23 reports after duplicate reconciliation (Table 1). Intervention-associated perturbation of CSF dynamics accounted for 15 published events, positional mechanisms for 10, spontaneous mechanisms for 3 and 1 event remained indeterminate. The present case was not added to either the intervention-associated or spontaneous published-case numerator. Instead, it was classified separately as a spontaneous-onset migration with peri-decompression progression/indeterminate event because the acute images documented migration during the hydrocephalus-EVD interval, while a CT from April 2024 provided evidence of spontaneous movement before any intervention.
Migration-focused reports included in the literature review
Table 1 Long description
The table lists 23 migration-focused reports and the number of extractable migration cases contributed by each. Baro et al. 2020 contributed one case and a review describing aqueduct-to-third-ventricle migration after endoscopic CSF diversion. Zee et al. 1980 contributed five cases involving positional mobility, foramen of Monro obstruction and intervention-associated migration. Zee et al. 1984 contributed two cases involving ventriculostomy-related third-to-fourth migration and an empty operative target. Kim and Weinberg 1985 contributed one spinal subarachnoid comparator illustrating mobility in CSF spaces. Martinez et al. 1989 contributed two lateral ventricular position changes on serial MRI. Ginier and Poirier 1992 contributed one lateral-to-third-to-fourth migration. Kramer et al. 1992 contributed one transaqueductal migration after lumbar puncture and pressure change. Neal 1995 contributed one preoperative third-to-fourth migration that changed the surgical route. Bergsneider et al. 2000 contributed one retrograde shunt-associated migration. Wray et al. 2001 contributed one cyst that escaped the expected third-ventricular target. Thomas and Krishnamoorthy 2005 contributed one migration during MRI acquisition. Araujo et al. 2008 contributed one lateral-to-third-ventricular migration. Kotha 2013 contributed one post-ventriculostomy migration. Ghosh et al. 2014 contributed one paradoxical migration after external ventricular drainage. Khalid et al. 2016 contributed one retrograde migration after ventriculoperitoneal shunting. Shah et al. 2017 contributed one sequential Monro-to-third-to-fourth migration. Rana et al. 2018 contributed one intermittent Monro obstruction with spontaneous retreat. Chugh et al. 2021 contributed one Brun-syndrome case. Singh et al. 2023 contributed one intraoperative migration. Agallo-Martinez et al. 2025 contributed one third-to-fourth migration after shunting. Mader et al. 2025 contributed one rapid third-to-fourth migration after external ventricular drainage. Apuzzo et al. 1984 contributed one uniquely extractable mobile lateral-ventricular case; overlapping cases were not double counted. Chowdhary et al. 2010 contributed one posterior-to-anterior third-ventricular migration after external ventricular drainage.
CSF, cerebrospinal fluid; EVD, external ventricular drainage; IVNCC, intraventricular neurocysticercosis; LP, lumbar puncture; VP, ventriculoperitoneal. Newly identified cohort/Brun-syndrome reports without extractable individual migration events were retained for contextual discussion but were not added to this pooled migration table.
Operative escape, non-visualization or a surgically empty ventricle was reported in 10/23 (43.5%) cases with operative detail. Permanent shunt placement was reported in 7/24 (29.2%) cases with available shunt outcome data, while clinical resolution or improvement was reported in 20/22 (90.9%) follow-up cases (Table 2). The chronology of the present case is summarized in Table 3.
Summary of the pooled review of published migrating ventricular neurocysticercosis cases
Table 2 Long description
The pooled descriptive synthesis contained 29 published cases with extractable individual data. Fifteen of 29 events, 51.7%, were temporally associated with an intervention affecting cerebrospinal fluid dynamics. Ten of 29, 34.5%, were positional. Three of 29, 10.3%, were spontaneous, and one of 29, 3.4%, had an unknown trigger. Brun syndrome was explicitly reported in 6 of 29 cases, 20.7%. Operative escape, non-visualization or an empty target occurred in 10 of 23 cases with operative detail, 43.5%. Permanent shunting was required in 7 of 24 cases with reported shunt outcomes, 29.2%. Clinical resolution or improvement occurred in 20 of 22 cases with reported follow-up outcomes, 90.9%. The present case was excluded from the trigger proportions and classified separately as peri-decompression or indeterminate.
These counts are descriptive and should not be interpreted as incidence estimates or procedure-specific causal risk estimates. The present case was not included in the published trigger proportions. It was classified separately as peri-decompression/indeterminate because migration was documented during the acute hydrocephalus-EVD interval, but the exact causal trigger could not be assigned.
Chronology of the present case
Table 3 Long description
The chronology begins with neuroimaging follow-up in 2011. MRI on 10 January 2023 showed a cyst in the body of the left lateral ventricle and led to a recommendation for endoscopic removal. CT on 30 April 2024 first showed subtle displacement that was not recognized at the time. CT on 14 August 2025 showed acute obstructive hydrocephalus with the cyst approaching the third ventricle before external ventricular drainage. CT on 15 August showed the lesion at the foramen of Monro, partly related to the left lateral and third ventricles, and CT on 16 August showed further caudal progression. MRI on 29 August and 22 October 2025 showed the cyst at the foramen magnum region. In January 2026, a midline suboccipital craniotomy was performed and the cyst was removed. The patient was discharged on postoperative day 6 with improved headache.
CT, computed tomography; EVD, external ventricular drainage; ICU, intensive care unit; MRI, magnetic resonance imaging.
The Embase and Cochrane update identified additional relevant IVNCC and Brun-syndrome literature, including larger endoscopic cohorts and clinical review series (Torres-Corzo et al., Reference Torres-Corzo, Rodriguez-della Vecchia and Rangel-Castilla2006; Shahani et al., Reference Shahani, Garnes and Mejia2015; Konar et al., Reference Konar, Kandregula, Sashidhar, Prabhuraj, Saini, Shukla, Srinivas, Indira Devi, Somanna and Arimappamagan2020; Xu et al., Reference Xu, Zhang, Guo, Xiong, Lang, Gan and Chen2025). These publications strengthened the contextual discussion of mobile cysts, emergent decompression, preoperative imaging and endoscopic management, but they did not provide additional individual intercompartment migration events meeting the predefined pooled-analysis criteria.
Discussion
Published pattern of migration
The central revision of this manuscript is the distinction between temporal association and causality. The additional outside-hospital images show that the patient had acute obstructive hydrocephalus and that the cyst was actively crossing the foramen of Monro/third ventricular region during the period in which rescue CSF diversion was required. The retrospective identification of cyst displacement on a CT scan from April 2024 – well before any CSF diversion – provides evidence that migration had a spontaneous component in this patient. However, this does not exclude the possibility that the acute hydrodynamic changes associated with EVD placement influenced the timing or trajectory of the subsequent caudal progression. The images from August 2025 document active relocation during the peri-decompression period but lack the temporal resolution to determine the exact contribution of each factor. The most defensible interpretation is therefore peri-decompression migration: active anatomical instability during the acute hydrocephalus-EVD interval, with evidence of a spontaneous baseline that may have been modulated by acute pressure changes.
This interpretation preserves the main clinical lesson while avoiding an unsupported causal claim. Mobile IVNCC behaves as a dynamic obstructive lesion: it may move spontaneously, after posture changes, during imaging, around CSF diversion or during surgery. In the present patient, the exact trigger cannot be assigned with certainty, but the location changed during the clinically decisive interval between deterioration, decompression and definitive treatment. In the broader descriptive literature assembled from case reports, trigger categories cannot be converted into procedure-specific risk estimates. They can, however, identify recurrent patterns that matter to surgical planning.
Large series and recent reviews emphasize that unattached ventricular cysts may present with abrupt obstructive symptoms, transient deterioration or head-movement-dependent phenomena, and that surgical planning becomes more complex when cyst mobility is suspected (Apuzzo et al., Reference Apuzzo, Dobkin, Zee, Chan, Giannotta and Weiss1984; Nash et al., Reference Nash, Ware and Mahanty2018; Baro et al., Reference Baro, Anglani, Martinolli, Landi, D’avella and Denaro2020; Hamamoto Filho et al., Reference Hamamoto Filho, Norcia, Fleury and Zanini2024; Mendieta-Barrera et al., Reference Mendieta-Barrera, Punukollu, Rios-hurtado, De Nigris Vasconcellos, Garcia-Torrico, Salolin-Vargas, Mamani-Julian, Valderrama, Rivera-Hurtado, Ballesteros-Herrera, Tripathi, Torres-Corzo and Ghaffari-Rafi2025). Recent endoscopic cohorts also reinforce the importance of high-quality preoperative localization and systematic imaging, including 3D heavily T2-weighted sequences, when ventricular or subarachnoid cysts may be difficult to visualize on conventional imaging (Konar et al., Reference Konar, Kandregula, Sashidhar, Prabhuraj, Saini, Shukla, Srinivas, Indira Devi, Somanna and Arimappamagan2020; Xu et al., Reference Xu, Zhang, Guo, Xiong, Lang, Gan and Chen2025).
Dynamic obstruction and the Brun spectrum
The revised image sequence also strengthens, rather than weakens, the interpretation of a Brun-spectrum event. The acute hydrocephalus was plausibly caused by migration-driven obstruction at a narrow CSF pathway during a period of active cyst relocation. Classic Brun syndrome requires clear position-dependent symptoms, which were not formally documented during the outside-hospital deterioration. Even so, the clinical sequence – sudden decompensation, acute obstructive hydrocephalus, interval movement from the lateral ventricle to the foramen of Monro/third ventricle and later caudal relocation – is consistent with migration-driven ball-valve obstruction.
This is aligned with a series of patients with third- or fourth-ventricular cysts presenting with intermittent intracranial hypertension and Brun syndrome, in which mobile deformable lesions can obstruct CSF pathways abruptly and may require urgent neurosurgical treatment (Torres-Corzo et al., Reference Torres-Corzo, Rodriguez-della Vecchia and Rangel-Castilla2006; Shahani et al., Reference Shahani, Garnes and Mejia2015; Chugh et al., Reference Chugh, Gotecha, Punia, Raghu, Patil and Kotecha2021). Thus, the case should be read less as proof of an iatrogenic trigger and more as a warning that a viable ventricular cyst can make ventricular anatomy unstable over a short interval.
Pressure gradients versus gravity
Gravity undoubtedly contributes to some migrations. Many positional cases occur during imaging, head turning, prone positioning or progressive descent towards the fourth ventricle (Zee et al., Reference Zee, Segall, Miller, Tsai, Teal, Hieshima, Ahmadi and Halls1980; Kim and Weinberg, Reference Kim and Weinberg1985; Martinez et al., Reference Martinez, Rangel-Guerra, Elizondo, Gonzalez, Todd, Ancer and Prakash1989; Kramer et al., Reference Kramer, Carrazana, Cosgrove, Kleefield and Edelman1992; Thomas and Krishnamoorthy, Reference Thomas and Krishnamoorthy2005; Shah et al., Reference Shah, Vutha, Sankhe and Goel2017; Baro et al., Reference Baro, Anglani, Martinolli, Landi, D’avella and Denaro2020). However, gravity alone is insufficient to explain all reported movements. The literature includes paradoxical or retrograde displacement after shunting, ventriculostomy, lumbar puncture or intraoperative manipulation (Kramer et al., Reference Kramer, Carrazana, Cosgrove, Kleefield and Edelman1992; Bergsneider et al., Reference Bergsneider, Holly, Lee, King and Frazee2000; Ghosh et al., Reference Ghosh, Al-khalili, Liu and Slasky2014; Khalid et al., Reference Khalid, Obaid, Sharma, Mahmood and Narayanasamy2016).
For this reason, the revised interpretation is broader and stronger than either a purely iatrogenic or purely spontaneous explanation. The present case does not prove that CSF diversion caused migration, but it also illustrates why spontaneous descent alone may be an incomplete model for mobile ventricular cysts during acute obstruction and decompression. The literature shows that CSF-altering procedures can coincide with or precede cyst relocation in selected reports. Gravity, posture, obstruction, ventricular compliance, narrow anatomical corridors and pressure gradients may interact to reshape the path of least resistance. The relevant clinical risk is therefore not a single causal mechanism, but the possibility that the cyst’s location at definitive surgery may differ from the location shown on earlier imaging.
Surgical implications
The operative lesson remains direct: a mobile IVNCC lesion is a moving target. Once migration is part of the differential, the surgeon should localize the cyst as close as feasible to definitive treatment, particularly after acute deterioration, CSF diversion, failed endoscopy or clinical change. Historical and contemporary reports have repeatedly underscored this point by showing clinically relevant interval migration between diagnostic imaging and surgery (Zee et al., Reference Zee, Segall, Apuzzo, Ahmadi and Dobkin1984; Neal, Reference Neal1995; Wray et al., Reference Wray, Ellis and Bianco2001; Mader et al., Reference Mader, Zekavaty, Yang, Rossi, Thompson and Mahmoud2025). The present case now provides a more granular version of the same message, because acute-phase CT narrowed the migratory interval and showed that the obstructive anatomy had already changed during the rescue period.
Management decisions should also reflect ventricular level and accessibility. Current guidelines and contemporary reviews support neuroendoscopic removal as the preferred strategy for most lateral and third ventricular cysts and, in experienced hands, for selected fourth ventricular lesions as well (Apuzzo et al., Reference Apuzzo, Dobkin, Zee, Chan, Giannotta and Weiss1984; White et al., Reference White, Coyle, Rajshekhar, Singh, Hauser, Mohanty, Garcia and Nash2018; Hamamoto Filho et al., Reference Hamamoto Filho, Norcia, Fleury and Zanini2024; Mendieta-Barrera et al., Reference Mendieta-Barrera, Punukollu, Rios-hurtado, De Nigris Vasconcellos, Garcia-Torrico, Salolin-Vargas, Mamani-Julian, Valderrama, Rivera-Hurtado, Ballesteros-Herrera, Tripathi, Torres-Corzo and Ghaffari-Rafi2025; Xu et al., Reference Xu, Zhang, Guo, Xiong, Lang, Gan and Chen2025). Yet once a lesion has descended to the caudal fourth ventricle or foramen magnum region, the most rational corridor may shift to a posterior fossa approach. In the present case, suboccipital surgery was not a failure of endoscopy; it was an adaptation to anatomy that had already changed.
Temporary CSF diversion should not be withheld when acute hydrocephalus or impending herniation is present. Even if CSF diversion can contribute to cyst relocation in some circumstances, the immediate risk of untreated intracranial hypertension exceeds that theoretical or technical concern. Reports of emergent IVNCC and Brun syndrome similarly emphasize that ventricular drainage or shunting may be necessary to stabilize the patient before definitive treatment (Shahani et al., Reference Shahani, Garnes and Mejia2015). The practical recommendation is therefore not to avoid necessary diversion and not to change emergency conduct but to pair decompression with hydrodynamic surveillance: repeat CT or MRI should be considered between rescue decompression and definitive surgery whenever feasible, because the cyst may have moved before, during or after the decompressive step.
Resource availability must also be acknowledged. High-resolution MRI may not be available in every emergency setting, and cost-effectiveness has not been studied. In lower-resource environments, a pragmatic approach may be to obtain at least a repeat non-contrast CT immediately before definitive surgery when MRI is unavailable, particularly when symptoms, ventricular calibre or operative planning no longer match the original scan.
Limitations
This report has limitations. First, although the newly obtained acute-phase CT images substantially reduce temporal uncertainty, they still do not provide continuous frame-by-frame documentation of the entire migratory route. The route from lateral ventricle to foramen magnum remains reconstructed from serial imaging and anatomy rather than directly filmed or captured in every compartment.
Second, the review is a focused narrative case-based synthesis rather than a registered systematic review. A formal systematic review was not the aim because the manuscript describes and contextualizes a rare migratory event rather than comparing diagnostic or therapeutic strategies. Although the search was updated using PubMed/MEDLINE, Embase and the Cochrane Library, the evidence base consists mainly of case reports and small series. It is vulnerable to publication bias, selective reporting, heterogeneous terminology and retrospective trigger classification. Third, the pooled numbers should not be read as risk estimates: there is no denominator of all IVNCC patients treated with EVD, shunt, lumbar puncture or endoscopy, and no comparator group of patients without CSF diversion. Fourth, many reports come from tertiary centres with advanced imaging and endoscopic expertise, which may limit generalizability.
These limitations do not invalidate the practical observation, but they define its level of inference. The data do not prove that EVD causes migration, and the present case should not be used to claim a purely spontaneous mechanism either. The clinically useful conclusion is more precise: mobile IVNCC can change location during the same interval in which patients deteriorate, are decompressed and are prepared for definitive surgery. The exact trigger may remain uncertain, but the moving anatomy is the operative problem.
Conclusions
Mobile IVNCC should be conceptualized as a dynamic obstructive lesion rather than a static ventricular cyst. In the present case, a CT scan from April 2024 documented spontaneous migration before any intervention, and the newly reviewed outside-hospital images showed active cyst progression during the acute hydrocephalus-CSF diversion interval. EVD was a necessary life-saving response to hydrocephalus; although the April 2024 CT confirms a spontaneous onset, the limited temporal resolution of the acute images does not allow us to determine whether the EVD modified the trajectory or speed of the caudal progression. The broader lesson remains hydrodynamic and surgical: in mobile IVNCC, ventricular anatomy may change rapidly before, during or after decompression. Urgent CSF diversion remains indicated when hydrocephalus is present, and repeat interval imaging before definitive surgery should be strongly considered whenever feasible.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0031182026102649.
Data availability statement
All data supporting this manuscript are contained within the manuscript and tables derived from the reviewed reports.
Acknowledgements
The authors thank the clinical teams involved in the patient’s care. Special thanks to Luciana Xavier Silva, radiologist from Fundação Instituto de Pesquisa e Estudo de Diagnóstico por Imagem, who was essential to find the additional outside-hospital imaging.
Author contributions
C.A.M.: data analysis and interpretation; drafting of the manuscript. A.G.D.S.: conception and design; acquisition of additional outside-hospital imaging; drafting of the manuscript; critical revision. K.G.O.S.: data analysis and interpretation. P.R.A.: imaging analysis and interpretation. C.G.C.J.: critical revision of the manuscript. F.C.G.P.: conception and design; critical revision; final approval.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Competing interests
The authors declare none.
Ethical standards
Written informed consent for publication was obtained from the patient.
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