Diagnosis and Management Approaches for Cerebellar Hydatid Cysts: A Systematic Review of Cases

Cerebellar hydatid cysts are uncommon lesions, with limited cases reported in the literature. This systematic review aimed to summarize current diagnostic and management approaches, given the low suspicion index of hydatid cysts in the cerebellum. The review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) under registration number CRD42023437853. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA-P) reporting guidelines. Two independent researchers searched PubMed, Scopus, and Google Scholar databases on June 27, 2023. We included 15 studies published between 1965 and 2022, comprising 12 case reports and three case series. A pooled analysis of reported cases (nine females and seven males) with cerebellar hydatid cysts revealed a mean age of 24 ± 20 years. Most of the cases were reported in Turkish hospitals (n = 8). The prominent signs and symptoms observed were headaches (10, 62.5%), ataxic gait (9, 56.25%), and visual disturbances (9, 56.25%). The time from symptom onset to hospital visit varied, with most patients seeking medical attention within the first three months. The left cerebellar hemisphere was the most common location of the cysts (6, 37.5%), and compression of the fourth ventricle was frequently observed. Computed tomography (CT) and magnetic resonance imaging (MRI) were the primary diagnostic tools used in three-fourths of cases, and surgical intervention was the primary treatment approach. Albendazole and praziquantel were commonly prescribed postoperatively, and two patients underwent preoperative needle decompression. This systematic review contributes to a better understanding of cerebellar hydatid cysts and guides future research and clinical management of this entity.


Introduction And Background
The prevalence and incidence of hydatid cysts and echinococcosis among zoonoses is increasing worldwide.The incidence of the main genus Echinococcus granulosus ranges from 1 to 220 cases per 100,000 inhabitants in endemic areas [1].A high prevalence has been reported in the Mediterranean, Russian Federation, China, Africa (Northern and Eastern Regions), Australia, and South America.The main sites for primary hydatidosis are the lungs and liver, but they can occur in any organ, including the brain, in 1% to 2% of all hydatidosis cases [1].Children are affected by 50% to 75% of intracranial hydatid cysts.Most recorded cases of intracranial hydatid cysts are located in cortical areas, specifically the parietal lobe.The mainstay of management involves surgical removal using the water-jet dissection technique [2].However, posterior fossa lesions are rare, and there is a paucity of literature on this topic.These cases have a unique course and treatment because of their proximity to several neuronal structures, such as the brainstem [3].The number of reported cases of cerebellar hydatid cysts with varying management approaches and high misdiagnosis rates remains unknown.This study aimed to provide a comprehensive overview of the patient characteristics, including symptoms, signs, complications, and strategies to manage these cases.

Review Methodology
This review was registered at the International Prospective Register of Systematic Reviews (PROSPERO) under CRD42023437853.This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA-P) guidelines [4].

Search Strategy
Two independent researchers performed a search on June 27, 2023, using PubMed, Scopus, and Google Scholar.The search string used for each database included the Medical Subject Heading (MeSH) database or other subject terms, search filters, and synonyms to optimize the keyword selection.The search strategy was peer-reviewed according to the PRESS (Peer Review of Electronic Search Strategies) guidelines [5].
Furthermore, the reference lists of the included studies were manually checked, and backward citation analysis was conducted.In case of missing data or if the full text is unavailable, the author/s were contacted via email to seek further clarification.Additionally, PROSPERO was checked using the terms ("Cerebellum") AND ("Hydatid cyst") to identify any ongoing studies.No time restrictions were applied and only English articles were searched.

Study Selection Criteria
We identified original case reports and case series as eligible study designs for our systematic review while excluding editorials, review articles, and other publications that did not report any primary data.Participants of any age, sex, ethnicity, or comorbidity with hydatid cysts in the cerebellum or cerebellar region were considered relevant for this review.Eligible studies were limited to those published in English.

Screening and Data Extraction
Studies retrieved from all databases were exported to Rayyan.ai, an online tool to identify and eliminate duplicate records [6].Subsequently, two independent authors assessed the remaining publications' titles, abstracts, and keywords to determine their eligibility for inclusion in this review.Then, the full texts of the publications that met the initial screening criteria underwent a thorough review to confirm their eligibility for inclusion in the review.Discrepancies were resolved by consensus or consultation with a third reviewer.Data extraction was performed independently by the same two reviewers using a standardized spreadsheet.The extracted data included study characteristics (author, year, country, and study design), participant characteristics (sample size, age, sex, and comorbidities), intervention/exposure, outcomes, and relevant findings related to the factors and risks associated with developing cerebellar hydatid cysts.Considering the heterogeneity of the included studies, we performed a narrative synthesis of the findings.The extracted data are presented in a tabular format, summarizing the factors and risks associated with the development of cerebellar hydatid cysts.

Quality Assessment and Risk of Bias
We assessed the risk of bias in the included studies using The Joanna Briggs Institute Critical Appraisal tools (JBI) (Appendix B).JBI assesses the methodological quality of the included studies.Disagreements were resolved by consensus or consultation with a third reviewer.However, we did not consider the quality of the study to be an inclusion criterion, and we included all studies with diverse quality scores.

Statistical Analysis
Data management and cleaning were conducted for all patients across the 15 case reports and series.Pooled descriptive analyses using frequencies and proportions were performed using IBM SPSS Statistics for Windows, Version 28.0 (IBM Corp., Armonk, NY).

Characteristics of Included Studies
The literature search yielded 1,051 articles, of which 61 were duplicates and 13 were removed for other reasons.Accordingly, 977 articles were screened in their title/abstract form and 957 were excluded for being irrelevant (not meeting the inclusion criteria).The remaining 20 articles were tested against the inclusion criteria in their full-text form, and five articles were excluded because of the unavailability of the full text.Finally, 15 articles were included in this systematic review, 12 of which were case reports and 3 case series were published between 1965 and 2022.Figure 1 shows a flowchart of the selection process.Table 1 presents the characteristics of the included studies.

Pooled Analysis of Reported Cases
The study included a total of 16 patients (nine females and seven males) who had cerebellar hydatid cysts, with a mean age of 24.1 ± 20.0 years, with median (interquartile range or IQR) = 16 (11.5 -27.5).All were reported by hospitals, except for five cases, and most reported cases were from Turkey (n = 8).The most frequent signs and symptoms were headaches (10, 62.5%), ataxic gait (9, 56.25%), and visual disturbances (9, 56.25%).In addition, patients frequently experienced vomiting (6, 37.5%), cranial nerve palsies (6, 37.5%), and nausea (4, 25%).Other positive cerebellar signs, such as lethargy and depressed reflexes, were also reported (8, 50%) (Table 1).The period from the onset of symptoms to hospital intervention varied among participants, as most patients showed symptoms within the first three months (10, 62.5%), while others came within one year, except for one patient who had symptoms for 14 years before seeking intervention.
Most cysts were located in the left cerebellar hemisphere (6, 37.5%).In addition, compression was most frequently reported in the fourth ventricle, with only three cases of calcification.Medical history and comorbidities were reported in a limited number of cases.Previous liver and lung hydatid cysts were reported in three cases, suggesting the risk of cerebellar hydatid cysts in previously exposed individuals.
Cystic lymphangioma, cerebellar abscess, cerebellitis, metastatic cerebellar tumor, cystic cerebellar tumor, cerebellar tuberculoma, and encephalitis were the differential diagnoses in the reported cases.The first interactions for diagnosis were CT and MRI, both of which were used in 12 cases (75%), which were, in most cases, confirmed postoperatively with lab results.The investigations and laboratory findings were mostly consistent across the studies.Based on the reported data, surgical intervention was the main treatment model in all cases, with variable approaches according to the cyst site, frequent use of albendazole and praziquantel postoperatively, and only two cases reported preoperative needle decompression.The treatment combinations used are presented in Table 2. Follow-up was uneventful in most cases (14, 87.5%), except in two patients.The characteristics of the included studies are summarized in Table 1.

Discussion
We report the first systematic review to provide a comprehensive overview of the current diagnostic and management strategies for cerebellar hydatid cysts.Most cases of central nervous system (CNS) echinococcosis, which represent 2%-3% of all hydatid cysts worldwide, affect children.In our review, we found seven occurrences of this condition in children.According to a previous systematic review of CNS hydatid cysts.Males have a higher prevalence of hydatid cysts than females; this may be because men work more in agriculture, which helps the condition spread.Additionally, because of hunting activities, males appear to come into contact with canines, such as dogs, wolves, and foxes, which are the specific hosts for Echinococcus.In contrast, no sex predominance was observed among the cerebellar cysts.More than onethird of CNS hydatid cyst cases have been reported in Turkey, which is consistent with our review of eight cases from Turkey [21].

Diagnosis of Cerebellar Hydatid Cysts
Diagnosing hydatid cysts can be challenging due to the nonspecific nature of imaging findings and the high rate of misdiagnosis, particularly when differentiating them from arachnoid cysts and epidermoid tumors, which also commonly occur in the posterior fossa [19].Hydatid cysts typically exhibit a spherical, round shape and have content with an attenuation value consistent with cerebrospinal fluid (CSF) [19].Notably, there was no contrast enhancement of the cyst wall, and perilesional edema was absent.Over time, these cysts have been observed to grow, leading to the compression and displacement of the surrounding brain parenchyma and neighboring structures.Consequently, patients may present with focal signs and/or symptoms indicative of raised intracranial pressure [22].This highlights the importance of carefully evaluating imaging results and considering the clinical context to achieve an accurate and timely diagnosis.This ensures appropriate management and treatment for patients with cerebellar hydatid cysts.
There were six cases of misdiagnosis in the included cases.The main differential diagnosis was cerebellar tumors, followed by arachnoid cysts and inflammatory changes.Cerebellar tumors are rare in adults [23]; therefore, cerebellar hydatid cysts must be considered when diagnosing adults with a mass lesion in the cerebellum.However, the cerebellum is the most common site for tumors in children younger than 15 [23], so it might be difficult to suspect hydatid cyst lesions.Five patients were under 15 years of age, two were misdiagnosed with cerebellar tumors, and one had a cerebellar abscess with cerebellitis.

Management of Cerebellar Hydatid Cysts
Managing cerebellar hydatid cysts primarily involves complete surgical excision, which is curative for the condition [24][25][26].Furthermore, the success of the surgical procedure depends on preventing incomplete excision and rupture during surgery, as these are the most common causes of recurrence and poor outcomes.One widely used surgical technique for resection is Dowling's method [27], which is known for its effectiveness.This procedure involves a frontoparietotemporal inverted U-incision that provides wide exposure.The dura was opened, and cortical dissection was performed.Using hydrodissection with saline, the cyst was carefully separated from the adjacent brain parenchyma until it was entirely removed with an intact capsule.To maintain appropriate positioning, the patient is placed in the left lateral position, and the head of the operating table is slightly tilted downward.After cyst removal, the cavity was filled with isotonic saline, and duraplasty was performed to ensure proper closure and healing [27].Lastly, for cases in the cerebellopontine angle and Meckles' cave, it is recommended to perform preoperative needle aspiration along with microsurgical dissection of the cyst due to adhesion of the cyst to several neuronal structures, such as the brain stem and lower cranial nerve, which was performed in two cases in our review [3,17].All cases in our systematic review utilized surgical excision, with no reported surgical complications.

Limitations
The limitations of this systematic review include the potential for publication bias, language bias, and variation in the quality of the included studies.Additionally, the review may be limited by the availability and quality of published literature on cerebellar hydatid cysts.We could not retrieve five studies, which adds to the limitations of this study.Furthermore, we excluded retrospective studies due to insufficient data.As most case reports are likely to focus on specific populations or healthcare settings, the generalizability of the findings to broader contexts may be limited.Future research should encourage multicenter collaboration and longitudinal studies to overcome these limitations and enhance the understanding of cerebellar hydatid cysts.

Conclusions
This systematic review aimed to provide comprehensive insights into the factors and risks associated with cerebellar hydatid cyst development.Furthermore, we compared different treatments and diagnostic modalities.The findings of this review may contribute to a better understanding of the disease and guide future research, clinical practice, and public health strategies.

FIGURE 1 :
FIGURE 1: Summary of study selection following the PRISMA flowchart.

TABLE 4 : JBI quality assessment tool for case reports.
JBI, Joanna Briggs Institute Critical Appraisal