In 2022, the Decree of the Government of the Russian Federation No. 565 “About approval of the Regulations on military-medical examination” dated 04.07.2013 was amended [1]. According to the document, brain MRI during the medical flight expert commission (VLEK) has first become mandatory for the citizens studying at the military educational institutions responsible for training of flight personnel of the state aircraft.

The analysis of the air force cadets’ first quantitative brain MRI results revealed high prevalence of various cerebrospinal fluid system alterations [2] representing the criterion for being unfit for flight training based on VLEK [1]. The data on the prevalence of alterations in the cerebrospinal fluid system of the brain among cadets were acquired during the study. That is why VLEK was given a task to determine the cadet’s category of fitness for further flight training.

All the non-neoplastic abnormalities and/or variants of the central nervous system (CNS) development showing no clinical manifestations or functional impairment represent the criterion of unfitness for flying duties used when conducting VLEK, regardless of the type of aircraft [1].

The study was aimed to assess the impact of retrocerebellar cysts in the brain on the pilot’s performance based on the comparative analysis of the brain MRI data of first-year air force cadets and air force pilots, who had successfully finished their flight duties.

METHODS

We used brain MRI data to assess the prevalence of retrocerebellar cysts among 348 (100%) first-year cadets studying at the Krasnodar Higher Military Aviation School of Pilots named after Hero of the Soviet Union A.K. Serov (median age was 19.0 years) during their first VLEK conducted at the 419th Military Hospital

(Krasnodar) between October 2022 and February 2023. Inclusion criteria: the first-year cadets admitted to the aviation school in 2022–2023 were included in the study. During the period when the cadets underwent MRI (October 2022 to February 2023), MRI was also performed in the retired air force pilots having no neurological complaints, who contacted the 419^th Military Hospital for outpatient care. We compared retrocerebellar cysts of the cadets and five military pilots in the reserve (median age 42.8 years), who had successfully finished their flight duties and undergone brain MRI. The clinical trial was conducted in accordance with the principles of the Declaration of Helsinki.

Brain structures were assessed using the open MRIAMICO300 scanner (AMICO; Russia) with the induction of 0.3 T. The standard brain MRI protocol was used [3]. All the acquired MRI scans (100%) were processed using the Machaon DICOM software tool.

Academic performance was assessed in accordance with the qualification requirements for professional military training of graduates.

Individual assessment of the cadets’ physical fitness was performed in accordance with the thematic plan of the Department of Physical Training of the aviation school. The following parameters of physical development were distinguished: speed (100 m race), strength (pull-ups), endurance (1 or 3 km race), and agility (shuttle run 10 × 10 m).

The results of professional psychological selection (PPS) conducted at admission to the military school were used to estimate the cadets’ professionally significant personality and intellectual qualities [4].

All the first-year cadets (n = 348) underwent brain MRI, no contrast agent was administered [3]. After selection, 100% of the cadets included in the study were divided into two groups based on the presence or absence of brain alterations in MRI. The group of patients having structural brain alterations consisted of 41 individuals; all the alterations found in the imaging region were assessed in order to find the most representative element that would be later defined as the object of research by the authors (retrocerebellar cysts found in 28 cadets).

Two groups of cadets were compared based on the following:

• estimates obtained when entering the aviation school and during the period of professional development (main academic disciplines and physical training);
• categories of professional psychological selection assigned when entering the aviation school;

“Adaptability” multilevel personality questionnaire designed to study adaptive capacity based on the assessment of certain psychophysiological and socio-psychological characteristics reflecting the integral features of the cadet’s mental and social development.

The non-contrast-enhanced brain MRI was also performed in five patients in the group of individuals in the reserve, among them two patients underwent assessment in other medical institutions. The remoteness of assessment did not exceed two weeks from the date of assessing the main population.

RESULTS

The diagnostic tests performed as part of VLEK in 348 firstyear cadets showed that the most prevalent cerebrospinal fluid system alterations were as follows: retrocerebellar cysts — 28 (8.2%), enlarged cerebrospinal fluid spaces — 3 (0.9%), asymmetry of the lateral ventricles — 3 (0.9%), septum pellucidum cyst — 3 (0.9%), internal hydrocephalus — 2 (0.6%), and temporal arachnoid cysts — 2 (0.6%). In the total sample of cadets, retrocerebellar cysts were found in 28 cases, the average cyst size was 9.5 mm (fig. 1).

At the same time, the routine examination of five military pilots in the reserve included in the total sample revealed retrocerebellar cysts in two cases, the average cyst size was 8.1 mm. Thus, an asymptomatic retrocerebellar cyst sized 9 × 11 mm was found in patient S. aged 42 years (total flight experience exceeding 1500 h, including 800 h on the Su-24 fighter) (fig. 2).

Comparison with the PPS data obtained at admission to the aviation school (tab. 1), academic performance scores for the main disciplines and physical performance obtained throughout the entire training period (tab. 2) was conducted in order to assess the CNS functional state in the cadets showing no MRI alterations (group 1) and cadets showing MRI alterations (retrocerebellar cysts) (group 2).

Pilots of group 1 were assigned PPS category 1 in 2% of cases, category 2 in 89% of cases, and category 3 in 9% of cases. Pilots of group 2 were assigned PPS category 2 in 100% of cases, which suggested functional adaptability of the cadets of group 2 (tab. 1).

The average scores for the main disciplines and physical training showed no significant differences between two groups of pilots (tab. 2).

The reasons for the first-year cadets’ expulsion from the higher aviation school were assessed in both groups in order to compare the cadets’ success (tab. 3).

There were 4 cadets (10%) discharged for health reasons (due to retrocerebellar cysts) after VLEK. Twice more first-year cadets of group 2 (with retrocerebellar cysts in MRI) resigned due to personal reasons after MRI compared to cadets showing no MRI alterations (tab. 3). This was due to high psychoemotional stress and concerns for further flight career among cadets of group 2, who had undergone brain MRI.

DISCUSSION

The data on the CNS functional state (brain MRI) and personal adaptive capacity assessed during the study showed that 100% of surveyed cadets had good performance and showed no significant differences, which suggests overestimation of the impact of retrocerebellar cysts on the category of fitness for flight duties [5].

The data provided are in line with the data of the other study [6] showing excessive demands on the presence of retrocerebellar cysts and no need for mandatory dismissal from flight duties based on VLEK.

The available literature provides wide coverage of the results [7] suggesting that the size and localization of masses in the retrocerebellar region  (retrocerebellar cysts) have no significant effect on the cerebrospinal fluid dynamics, and their clinical significance is poorly understood, which is in line with the data provided.

It should be noted that the presence of accidentally discovered cysts in two pilots in the reserve having a decent history of service, long flight experience on various types of aircraft and discharged from military service not for health reasons confirms the hypothesis about the negligible impact of retrocerebellar cysts found in pilots on their performance and professional longevity.

CONCLUSIONS

The findings undoubtedly require further research. However, the patterns revealed raise additional issues related to prediction of the impact of retrocerebellar cysts on the pilot’s category of fitness determined during VLEK.

It is necessary to continue the research in order to gain the body of evidence and provide the possibility to predict the effects of retrocerebellar cyst in the brain on the cadets’ performance and professional longevity.