Topography and macroscopic structure
The glands are located in the adrenal fossa and are surrounded on all sides by retroperitoneal adipose tissue (periadrenal fat). Externally, the organ is covered by a thin capsule containing lymphatic vessels (there are no lymphatic pathways within the gland parenchyma itself).
Anatomically and functionally, the adrenal gland is a complex of two neuroendocrine structures with fundamentally different origins:
- Adrenal cortex (cortex) — develops from the mesoderm.
- Adrenal medulla (medulla) — has a neuroectodermal origin.
Normally, the average dimensions of the gland are 5 × 3 × 1 cm, and its weight ranges from 4 to 6 g. It is important to note that prolonged exposure to stress can trigger processes of hypertrophy and hyperplasia, leading to an increase in the mass and volume of the organ.
Blood supply characteristics
Arterial inflow is characterized by multiple sources. In classical anatomy, the gland receives blood from three basins:
- The superior suprarenal artery arises from the inferior phrenic artery.
- The middle suprarenal artery arises directly from the abdominal aorta.
- The inferior suprarenal artery is a branch of the renal artery.
Venous drainage, conversely, is asymmetric. The short right suprarenal vein drains directly into the inferior vena cava (IVC). The longer left suprarenal vein empties into the left renal vein, and anatomical variations with its direct drainage into the IVC are rare.
Radiological semiotics: CT and MRI
On axial tomograms, the organ has a characteristic configuration. It consists of the body (body), as well as the medial and lateral limbs (limbs). The normal thickness of the limbs does not exceed 5 mm. The maximum size of the body for the right adrenal gland is $\le$ 10 mm, and for the left $\le$ 8 mm.
- CT findings: Unaltered glandular tissue demonstrates intense and uniform contrast enhancement in both the arterial and venous phases of scanning.
- MRI findings: T1-weighted images show a homogeneous intermediate signal, while T2-WI show a hypointense (low to intermediate) signal. Optimal visualization is achieved on T1-WI with fat suppression (fat saturation), as this "darkens" the surrounding retroperitoneal fat and clearly highlights the hyperintense gland.
Due to the widespread use of CT, incidental masses—incidentalomas—are frequently detected. They are found in 5% of routine abdominal scans and 2% of low-dose chest CT scans. Most of them are benign (myelolipomas, cysts, adenomas, hematomas), but malignant lesions (metastases, adrenocortical carcinoma, pheochromocytoma) also occur. The radiologist's task is to differentiate these conditions.
Physiology and histological structure of zones
The adrenal cortex synthesizes corticosteroids (cholesterol derivatives) and is divided into three layers from outside to inside:
- Zona glomerulosa (zona glomerulosa): produces mineralocorticoids (primarily aldosterone). The process is regulated predominantly by angiotensin II.
- Zona fasciculata (zona fasciculata): synthesizes glucocorticoids (primarily cortisol, which regulates carbohydrate, lipid, and protein metabolism). It is regulated by adrenocorticotropic hormone (ACTH).
- Zona reticularis (zona reticularis): is responsible for the secretion of androgens and estrogens. It is also regulated by ACTH.
The medulla consists of chromaffin cells. It synthesizes catecholamines (norepinephrine and epinephrine) in response to impulses from the sympathetic nervous system. The medulla is the main source of norepinephrine in the body alongside paraganglia, specifically the organ of Zuckerkandl, which is located near the bifurcation of the abdominal aorta.
Briefly: answers to topical questions
Which lymph nodes are regional for the adrenal glands?
Regional lymph nodes for the adrenal glands include the para-aortic lymph nodes, paracaval lymph nodes, and lumbar lymph nodes (nodi lymphoidei lumbales). The lumbar nodes form groups along major retroperitoneal vessels: the left lumbar nodes lie along the left side of the aorta, the right lumbar nodes along the inferior vena cava, and the intermediate lumbar nodes between the aorta and the inferior vena cava.
Which contrast-enhancement phases are used in adrenal CT for the differential diagnosis of adenomas?
For the differential diagnosis of adrenal lesions and the assessment of contrast washout, the following CT phases are used:
- Unenhanced phase (unenhanced) — measurement of lesion density before contrast administration.
- Contrast-enhanced CT (CECT) — measurement of density 60 seconds after the start of intravenous contrast administration.
- Delayed phase (delayed attenuation) — measurement of density 15 minutes after contrast administration to calculate absolute or relative contrast washout.
Which organs are in syntopic relation with the right adrenal gland?
The right adrenal gland has a pyramidal shape and is located in the adrenal fossa. Syntopic relations of the right adrenal gland include the following structures:
- Liver (hepar) — the extraperitoneal surface of the liver lies anteriorly.
- Inferior vena cava (vena cava inferior) — medially, the right adrenal gland is in contact with the inferior vena cava and runs along its medial border.
For quick memorization of adrenal shape: R-P and L-C. Right — Pyramidal, Left — Crescentic.
Class and exam questions
Can the cortex and medulla be visually separated on CT or MRI?
No, modern diagnostic imaging methods do not allow for visual differentiation of these zones.
What improves the visualization of the adrenal glands on MRI?
Through the use of fat-suppression sequences (Fat Saturation). This nullifies the signal from the periadrenal fat and highlights the gland itself.
What is the radiological differential diagnosis of incidentalomas?
The key task is to determine the nature of the incidental finding: to distinguish benign changes (adenomas, myelolipomas, cysts) from malignant ones (metastases, adrenocortical carcinoma).
What else to study on this topic
- Radiological patterns of benign lesions: adenomas and myelolipomas
- CT semiotics of malignant lesions and metastases
- CT protocols for assessing contrast washout
- Pheochromocytoma and paragangliomas: imaging features
- Adrenocortical carcinoma: radiological signs of malignancy
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