Isolated Mega Cisterna Magna: A Preliminary Study from Eastern Iran

Abstract

Background The clinical significance and incidence of isolated mega cisterna magna (MCM) have been thoroughly investigated. While MCM has been reported in association with psychiatric disorders in adults, current study sought to report its incidence and relationship with gender and age in a consecutive series of patients without psychiatric comorbidities.

Materials and Methods We retrospectively reviewed 1,016 consecutive computed tomography scans of patients between the age of 1 and 80 with a history of minor head trauma, headache, or vertigo from April to August 2023. Two perpendicular diameters inside the MCM were measured: the first diameter (D₁) was measured longitudinally on the midsagittal plane (anteroposterior diameter), whereas the second one (D₂) was measured transeversely (transverse diameter). An MCM with D₁> 20 mm was defined as “huge MCM.” The relationship between age, gender, and the two diameters were subsequently analyzed.

Results Over a course of 5 months, 92 cases with MCM, including 76 men, were evaluated. The mean age of MCM cases was 35.31 ± 26.14, with no significant relationship observed between age and MCM. No significant difference in D₁ was found between genders, while D₂ significantly differed between men and women (p < 0.029). “Huge MCM” was exclusively observed in 18 men (p < 0.035). There was also no significant correlation between D₁ and D₂.

Conclusion MCM appears to be a normal variation in the general population with no clinical significance. Despite the small sample size, the current study can provide a foundation for further studies to investigate the correlation of isolated MCM with different aspects of cognitive functions and its potential clinical relevance.

Keywords

computed tomography scan - mega cisterna magna - normal population - normal variation - preliminary study

Introduction

The cisterna magna refers to the subarachnoid space situated behind the medulla oblongata, beneath the cerebellum. This space facilitates to the transfer of cerebrospinal fluid (CSF) from the fourth ventricle to the foramina. Mega cisterna magna (MCM) is considered a cystic posterior fossa malformation characterized by enlarged cisterna magna (larger than 10 mm) on midsagittal images (anteroposterior view), an intact cerebellar vermis and hemispheres, and the absence of hydrocephalus.[1] [2] [3] Various entities such as persistent Blake's pouch cyst, Dandy–Walker spectrum, and posterior fossa cysts and neoplasia are considered to be the differential diagnoses of MCM.[4]

There is a paucity of information regarding the incidence and clinical importance of isolated MCM in individuals without psychiatric symptoms in the literature, as it is often an incidental radiographic finding on brain imaging (magnetic resonance imaging [MRI] or computed tomography [CT]) conducted for unrelated reasons.

Isolated MCM in adults was found to be associated with impairment of various parameters of memory and verbal functions. Although the cooccurrence of MCM and psychiatric disorders has been reported, albeit infrequently, the nature of their relationship remains largely unknown.[5] [6] [7]

To the best of our knowledge, no prior study has investigated the incidence of isolated MCM in a developing country, aiming to establish a foundation for future studies on some untouched aspects of MCM.

Materials and Methods

This cross-sectional study was conducted in accordance with the Helsinki Declaration and was approved by our institutional ethical committee. We retrospectively reviewed 1,016 consecutive brain CT scans obtained from April to August 2023. Individuals between the ages of 1 and 80 years old who underwent brain CT for headache, vertigo, or minor head trauma were included in our study. Patients with loss of consciousness and moderate or severe head trauma were excluded. For each brain CT scan, we measured two perpendicular diameters inside the cisterna magna. The first diameter (D₁) measured was the anteroposterior diameter, longitudinally on the midsagittal plane diameter, while the second diameter (D₂) was the transverse diameter. Based on pertinent literature,[8] MCM was diagnosed when the longitudinal diameter is more than 10 mm on midsagittal planes. In addition, we assigned the term “huge MCM” to those with a longitudinal diameter of > 20 mm ([Fig. 1]). The relationship between age, gender, and two diameters was analyzed thereafter.

Fig. 1 (A) Brain computed tomography (CT) of nonhuge isolated mega cisterna magna (MCM). (B) Brain CT of huge MCM.

Statistical Analysis

Statistical analysis involved independent two-sample t-tests to compare diameters between sexes and their relationship with age. Pearson's correlation analysis was also conducted to assess the strength of relationships between diameters and age. p-Values were calculated to determine significance, with a level of 0.05 used for evaluation. Data visualization was performed using with the Seaborn library (version 0.11.2) and Matplotlib (version 3.4.3) in Python.

Results

Over a 5-month period, 1,016 brain CT scans were assessed, with 555 (54.6%) of the subjects being male. MCM was identified in 92 cases (9.1%), demonstrating a significant male predilection (p < 0.0001), as 76 cases (82.6%) occurred in men. The mean age of individuals with MCM was 35.31 ± 26.14 years, and no significant relationship between MCM and age was observed (p = 0.296) ([Fig. 2]). The anteroposterior diameter (D₁) measured was 16.66 ± 4.99 mm in men and 15.78 ± 3.56 mm in women, with no significant difference between genders (p = 0.415). However, the transverse diameter (D₂) measured 18.64 ± 7.01 mm in men and 15.71 ± 4.05 mm in women, showing a significant difference between the two genders (p = 0.029) ([Fig. 2]). Additionally, cases with a D₁ greater than 20 mm, categorized as “huge MCM,” were observed exclusively in 18 men (p = 0.035) ([Fig. 2]).

Fig. 2 Distribution of mega cisterna magna (MCM) patients and comparison of anteroposterior diameter and transverse diameter across different sexes and ages.

No significant correlation was observed between the anteroposterior (D₁) and transverse (D₂) diameters (correlation coefficient = 0.54). The distributions of the anteroposterior (D₁) and transverse (D₂) diameters for both “huge” and “nonhuge” MCM are illustrated in [Fig. 3].

Fig. 3 Distribution and correlation of anteroposterior diameter and transverse diameter in huge mega cisterna magna (MCM) and not huge MCM.

Discussion

The cisterna magna is a subarachnoid space located under the inferior surface of the cerebellum at the rear of the medulla oblongata. CSF flows from the fourth ventricle through the foramen of Magendi by means of cisterna magna.[1]

The incidence of MCM, particularly in cases of isolated MCM, has not been thoroughly investigated in the general population due to the fact that brain imaging is typically only performed on individuals with specific concerns. Consequently, there is a lack of sufficient data on the overall incidence of MCM, making it a contentious topic in the medical community. It was found that MCM is associated with an increased incidence of psychiatric disorders.[6] [9] [10] [11] In this study, we conducted our research on a general population with no history or presence of psychiatric disorders.

In a study conducted by Bodensteiner et al,[12] 1,260 consecutive brain CT scans of individuals with ages ranging from 1 month to 19 years were assessed, identifying 14 cases of isolated MCM. Of them, eight cases (62%) exhibited signs of long-term neurological dysfunction. Pollak et al[13] reported seven cases with posterior fossa anomaly associated with neuropsychiatric disorders, including one of individual with schizoid personality traits and another one experiencing head and trunk tremors, both of which significantly impacted social and professional life.

Ek et al[14] conducted an extensive sonographic anatomical assessment of 11,145 fetuses at 21 weeks of gestation. Isolated MCM was identified in only three fetuses, all of whom demonstrated satisfactory neonatal outcomes. Similarly, Haimovici et al[15] reviewed 15 fetuses with sonographically confirmed diagnosis of isolated MCM. The phenotype of all the cases was entirely normal, with no signs of neurological disorder. Long-term follow-up, ranging from 2 to 89 months, was available in eight cases, none of which showed any evidence of developmental delay, neurological disorders, or abnormalities in the brain or posterior fossa.

In diagnosing and detecting isolated MCM, both MRI and CT are commonly utilized, each with distinct advantages and limitations.[16] CT is valuable for its high spatial resolution, enabling clear visualization of bony structures and gross brain anatomy. However, its capacity for soft tissue differentiation is limited compared with MRI, making CT less sensitive to the fine structural details and subtle variations within the posterior fossa.[17] Consequently, CT may miss certain characteristics of MCM, particularly when distinguishing it from other posterior fossa cystic lesions, such as arachnoid cysts or Dandy–Walker malformations. While CT can provide initial insight into the enlarged cisterna magna, it lacks the specificity required for a comprehensive evaluation of isolated MCM. MRI, by contrast, offers superior sensitivity and specificity for soft tissue differentiation and is the preferred imaging modality for assessing posterior fossa anomalies. Its high contrast resolution allows for detailed visualization of the cisterna magna and adjacent structures, enabling accurate identification of isolated MCM and distinguishing it from similar conditions. While MRI is the preferred choice for detailed evaluation of MCM, CT scans remain widely used in clinical settings due to their accessibility, speed, and effectiveness in visualizing osseous structures. CT imaging is often an essential tool for initial screenings and follow-ups, particularly in facilities where MRI may be less accessible.[18]

Zimmer et al[1] reviewed 19,301 consecutive brains MRI and CT scans and reported 49 cases of isolated MCM. Their study aimed to determine the cognitive profile of adults (aged 18 years and older) with isolated MCM. A battery of neuropsychological tests was administered to 18 adults with confirmed MCM and on 18 control cases with no brain abnormalities. The incidence of isolated MCM reported was 0.25% (2.5 per 1,000) in their cohorts. While the authors concluded that adults with isolated MCM generally exhibited normal cognitive functioning, some performed less well than the control group in specific memory and verbal fluency parameters.

After reviewing 9,400 CT scans, Kars et al[19] reported an incidence rate of 0.33% for MCM and identified a strong association between this anomaly and cerebral atrophy. In our study, we observed 92 cases (9.1%) of MCM, with a significant male predominance, after reviewing 1,016 brain CT scans over a 5-month period. The higher incidence in our study may be attributed to increased likelihood of misdiagnosed MCM cases on CT scans compared with MRI.[12] We measured two diameters of cisterna magna and found a significant gender difference in relation to anteroposterior diameter (D₁). Additionally, we introduced “huge MCM” for cases with a D₁ larger than 20 mm and identified 18 men with such cases, all occurring in males. The primary limitation of our study was the relatively small sample size. Unlike to Zimmer et al,[1] we did not perform cognitive assessments to evaluate the clinical significance of isolated MCM. Furthermore, by excluding cases with loss of consciousness, we were unable to fully mitigate the potential for selection bias. Other limitations include the exclusive use of CT scans. Future research could incorporate MRI and other modalities to explore their advantages and disadvantages.

Conclusion

It appears reasonable to infer that isolated MCM may be a normal anatomical variation in the general population with no clear clinical significance. Although our small sample size limits the strength of this conclusion, our findings provide a basis for future research to explore the potential correlation between isolated MCM and various cognitive functions, as well as its possible clinical implications.

Conflict of Interest

None declared.

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Publikationsverlauf

Artikel online veröffentlicht:
17. Januar 2025