1. Background
The adrenal glands are a pair of endocrine organs that produce several essential hormones, including catecholamines such as epinephrine and norepinephrine, as well as steroid hormones like aldosterone and cortisol. Each gland comprises two main parts: The cortex (outer layer) and the medulla (inner core), with the cortex being responsible for steroid hormone production (1).
The adrenal cortex consists of three distinct zones: The zona glomerulosa, zona fasciculata, and zona reticularis. These zones produce three major classes of steroid hormones — mineralocorticoids, glucocorticoids, and androgens, respectively (2, 3).
Each adrenal gland typically weighs about 5 grams. However, the average weight in adult humans ranges between 7 and 10 grams. The glands are approximately 5 cm in length, 3 cm in width, and about 1 cm in thickness (4, 5).
Numerous endocrine disorders are associated with adrenal dysfunction. Excessive cortisol production results in Cushing's syndrome, whereas insufficient cortisol secretion causes Addison's disease (6, 7). A genetic disorder known as congenital adrenal hyperplasia (CAH) results from disruptions in normal endocrine function. Additionally, adrenal tumors — benign or malignant — may be identified through medical imaging techniques such as computed tomography (CT) (8-10).
Each of these disorders can lead to structural changes, including alterations in the size and morphology of the adrenal glands. Indeed, diffuse adrenal enlargement is a commonly observed feature in CT reports of various pathological conditions (11, 12). Therefore, establishing normal size references — especially adrenal thickness — is crucial for accurate interpretation of imaging results and diagnosis (13, 14).
2. Objectives
Despite its importance, available data on the normal size of adrenal glands remain limited, and such information has not yet been studied specifically in the Iranian population. Accordingly, the aim of this study is to evaluate and establish the normal thickness of the adrenal glands using computed tomography in healthy Iranian adults.
3. Methods
This study, as a cross-sectional-analytical study, was conducted on healthy people in terms of adrenal glands. Based on this, patients who had undergone abdominal CT as their evaluation were considered as the study group. Cases with the stated exclusion criteria were excluded from the study.
CT studies included thin-slice images (slice thickness ≤ 2.5 mm). The indices evaluated in CT included maximum adrenal thickness and internal and external bases perpendicular to the axis, which were measured in both adrenal glands. Measurements were recorded in millimeters to the nearest decimal point in the checklist.
3.1. Inclusion and Exclusion Criteria
Inclusion criteria: (1) Age > 18; (2) Iranian nationality; (3) having a CT scan of the abdomen.
Exclusion criteria: (1) All patients with clinical, biochemical, or radiological evidence of adrenal disease; (2) patients who had a history of chronic steroid use; (3) incompleteness of file information.
3.2. Ethical Consideration
This study is approved under the ethical approval code IR.IUMS.FMD.REC.1401.163.
3.3. Statistical Evaluation
The information obtained from the evaluated samples was recorded in the checklist. Then, the obtained information was entered into SPSS version 24 software. Quantitative data were checked using mean and standard deviation, and qualitative data using percentage and frequency. Then, an independent sample t-test was used to compare between two sides and gender, and based on this, adrenal size and thickness were compared based on gender and the side of the glands.
4. Results
In this evaluation, 500 healthy cases who met the necessary inclusion criteria were selected, and then the cases were evaluated. Based on the evaluations performed on the population and in accordance with the study objectives, the information obtained regarding adrenal thickness in different parts of the right and left adrenals was assessed.
The mean and standard deviation of the thickness of the right adrenal gland was 6.40 ± 1.05, and that of the left adrenal was 6.21 ± 1.12. Based on the statistical evaluation and the independent t-test, there was a statistically significant difference between the two sides (P = 0.001). The size of the adrenal gland was larger on the right side than on the left. The mean and standard deviation of the thickness of the lateral limb of the right adrenal was 4.23 ± 0.87, and in the left adrenal was 3.61 ± 0.83. Based on the statistical evaluation, there was a statistically significant difference between the two sides (P = 0.001), and the size of the lateral limb on the right side was larger than the left. The thickness of the medial adrenal limb was 3.91 ± 0.85 on the right side and 3.68 ± 0.89 in the left adrenal. Based on the statistical evaluation, there was a statistically significant difference between the two sides (P = 0.001), and the size of the medial adrenal limb was also larger on the right side than on the left side (Table 1).
Table 1.Mean and Standard Deviation of Thickness in Right and Left Adrenal
| Variables | Values | P -Value | |
|---|---|---|---|
| Mean | SD | ||
| Body | 0.002 | ||
| Right | 6.40 | 1.05 | |
| Left | 6.21 | 1.12 | |
| Lateral Limb | 0.001 | ||
| Right | 4.23 | 0.87 | |
| Left | 3.61 | 0.83 | |
| Medial Limb | 0.001 | ||
| Right | 3.91 | 0.85 | |
| Left | 3.68 | 0.89 | |
Also, the mean and standard deviation of the size of the lateral limb in the right (P = 0.001) and left (P = 0.001) adrenals in males were significantly higher than in females. Additionally, the size of the medial limb in the right (P = 0.01) and left (P = 0.02) adrenals was significantly greater in males than in females. On the other hand, the size of the adrenal gland in both right (P = 0.04) and left (P = 0.03) adrenals was larger in males, and this difference was statistically significant (Table 2).
Table 2.Mean and SD of Adrenal Gland Thickness and Medial and Lateral Right and Left Limbs According to Gender
| Adrenal Sizes | Gender | P-Value | |
|---|---|---|---|
| Male | Female | ||
| Lateral Limb | |||
| Right | 0.84 ± 4.45 | 0.84 ± 3.87 | 0.001 |
| Left | 0.85 ± 3.95 | 0.79 ± 3.58 | 0.001 |
| Medial Limb | |||
| Right | 0.84 ± 4.12 | 0.79 ± 3.65 | 0.01 |
| Left | 0.75 ± 3.95 | 0.69 ± 3.55 | 0.02 |
| Body | |||
| Right | 1.09 ± 6.85 | 0.99 ± 6.38 | 0.04 |
| Left | 1.09 ± 6.45 | 1.10 ± 6.05 | 0.03 |
5. Discussion
Anatomically, adrenal glands are structures that are located bilaterally in the extraperitoneal space around the kidney. Each of these glands is surrounded by a fatty capsule and renal fascia. Functionally, despite their small size, the adrenal glands are vital endocrine glands. Determining adrenal volume has been possible in recent years. Adrenal thickness, rather than volume, is still considered a useful parameter for evaluating suspected adrenal pathology.
Based on the present study, the mean and standard deviation of the thickness of the right adrenal gland was 6.40 ± 1.05 and that of the left adrenal gland was 6.21 ± 1.12 (P = 0.001); the size of the right adrenal gland was larger than the left. The mean and standard deviation of the thickness of the lateral limb of the right adrenal was 4.23 ± 0.87 and that of the left adrenal was 3.61 ± 0.83 (P = 0.001), and the size of the lateral limb on the right side was significantly larger than the left. On the other hand, the mean and standard deviation of the thickness of the right medial adrenal limb was 3.91 ± 0.85 and that of the left adrenal was 3.68 ± 0.89 (P = 0.001), and the size of the medial adrenal limb was larger on the right side than the left. On the other hand, all measured items in the male gender were significantly larger than in the female gender.
Bagheri et al. also stated that visual scores for normal adrenal activity ranged from 0 to 3 and maximum SUVs ranged from 0.95 to 2.46. The visual score of adrenal activity was well correlated with average and maximum SUV (average SUV vs. visual score: 0.96, r = 0.88; maximum SUV vs. visual score: 0.99, r = 0.87) (15); however, these indices were not examined in the recent evaluation. Devakar et al. also stated that the mean maximum thickness of the right adrenal gland, medial base, and lateral side were 7.16 ± 1.67, 4.23 ± 1.45, and 4.45 mm. The difference in all measurements on the left was larger than the right, and this difference was statistically significant (P < 0.001) (16); however, in the recent evaluation, both right and left sides were compared.
Wang et al. evaluated the normal size of the adrenal gland in healthy cases and observed that the total volume of the left, right, and total size of adrenal glands was 4.23 ± 0.74 (range: 2.85 - 5.83), 0.86 ± 4.26 (6.56 - 2.59), and 8.50 ± 1.40 (5.80 - 11.39) cm3, respectively (17); however, some of these indicators have not been evaluated in the recent study, which justifies the difference observed between the two studies. Vincent et al. (1994) also evaluated the size of the normal adrenal gland in a study and observed that the average measurements for the right adrenal gland were: Maximum width 0.61 mm (SD = 0.2), inner base width 0.28 mm (SD = 0.08), and lateral base width 0.28 mm (SD = 0.06) (18); however, in the recent evaluation compared to Vincent et al.’s study, it has been observed that the values in the right adrenal gland were higher. Also, John et al., by evaluating the normal thickness of the adrenal gland, observed that the average lateral and medial side maximum thickness of the adrenal gland was 3, 4.1 ± 1.1, and 7.2 ± 1.8, respectively. They observed a statistically significant difference (P = 0.0001) (19), which, like the recent evaluation, showed that the thickness of the left adrenal gland was greater than the right, and this had a statistically significant difference. In these studies, adrenal thickness has been evaluated in different populations; based on this and according to these results, a resource can be designed to evaluate patients compared to healthy individuals.
5.1. Conclusions
Based on the results observed in this evaluation, the mean and standard deviation of the thickness of the right adrenal gland was 6.40 ± 1.05 and in the left adrenal gland was 6.21 ± 1.12 (P = 0.001). The mean and standard deviation of the thickness of the right adrenal gland lateral limb was 4.23 ± 0.87 and 3.61 ± 0.83 in the left adrenal gland (P = 0.001), and the size of the right adrenal gland was larger than the left. Also, the mean and standard deviation of the right medial adrenal gland thickness was 3.91 ± 0.85 and in the left adrenal gland was 3.68 ± 0.89 (P = 0.001). So, all values in the right adrenal were higher than in the left adrenal. Based on the results of the recent evaluation, the normal value of adrenal thickness in the right and left adrenal glands of adults has been determined, and based on this, it will be possible to compare it with patients.
