Suprarenal (adrenal) gland

RIGHT SUPRARENAL GLAND

The right suprarenal gland lies posterior to the inferior vena cava, from which it is only separated by a thin layer of fascia and connective tissue. It lies posterior to the right lobe of the liver and anterior to the right crus of the diaphragm and superior pole of the right kidney (Fig. 72.2). Its inferior surface is referred to as the base and adjoins the anterosuperior aspect of the superior pole of the right kidney. It often overlaps the apex of the upper pole of the right kidney as the two lower projections (limbs) straddle the renal tissue. The anterior surface faces slightly laterally and possesses two distinct facets. The medial facet is somewhat narrow, runs vertically and lies posterior to the inferior vena cava. The lateral facet is triangular and lies in contact with the bare area of the liver. The lowest part of the anterior surface may be covered by peritoneum, reflected onto it from the inferior layer of the coronary ligament. At this point it may lie posterior to the lateral border of the second part of the duodenum. Below the apex, near the anterior border of the gland, the hilum lies in a short sulcus from which the right suprarenal vein emerges to join the inferior vena cava. This vein is particularly short, which makes surgical resection of the gland potentially hazardous, because ligation may be difficult. The vein may be avulsed from the inferior vena cava during surgery or occasionally by high-energy deceleration injuries. The posterior surface is divided into upper and lower areas by a curved transverse ridge. The large upper area is slightly convex and rests on the diaphragm. The small lower area is concave and lies in contact with the superior aspect of the upper pole of the right kidney. The medial border of the gland is thin and lies lateral to the right coeliac ganglion and the right inferior phrenic artery as the artery runs over the right crus of the diaphragm.

Fig. 72.2 A, Axial T1 weighted and B, Coronal T2 weighted MRI of the suprarenal glands. (Supplied by Dr Louise Moore, Chelsea & Westminster Hospital.)

LEFT SUPRARENAL GLAND

The left suprarenal gland lies closely applied to the left crus of the diaphragm and is separated from it only by a thin layer of fascia and connective tissue (Fig. 72.2). The medial aspect is convex whilst the lateral aspect is concave since it is shaped by the medial side of the superior pole of the left kidney. The superior border is sharply defined while the inferior surface is more rounded. The anterior surface has a large superior area covered by peritoneum on the posterior wall of the lesser sac, which separates it from the cardia of the stomach and sometimes from the posterior aspect of the spleen. The smaller inferior area is not covered by peritoneum and lies in contact with the pancreas and splenic artery. The hilum faces inferiorly from the medial aspect and is near the lower part of the anterior surface. The left suprarenal vein emerges from the hilum and runs inferomedially to join the left renal vein. The posterior surface is divided by a ridge into a lateral area adjoining the kidney and a smaller medial area which lies in contact with the left crus of the diaphragm. The convex medial border lies lateral to the left coeliac ganglion, and the left inferior phrenic and left gastric arteries, which ascend on the left crus of the diaphragm.

VASCULAR SUPPLY AND LYMPHATIC DRAINAGE

Arteries

The suprarenal glands have an extensive vascular supply in relation to their size. Each gland is supplied by superior, middle and inferior suprarenal arteries, whose main branches may be duplicated or even multiple (Fig. 72.3). They ramify over the capsule before entering the gland to form a subcapsular plexus, from which fenestrated sinusoids pass around clustered glomerulosal cells and between columns in the zona fasciculata to a deep plexus in the zona reticularis. Venules from this plexus pass between medullary chromaffin cells to medullary veins, which they enter between prominent bundles of smooth muscle fibres. Some relatively large arteries bypass this indirect route and pass directly to the medulla (Fig. 72.4). At operation the arteries are rarely obvious, but the veins deserve specific attention (see below).

Fig. 72.3 Arterial supply and venous drainage of the suprarenal glands.

(From Drake, Vogl and Mitchell 2005.)

Fig. 72.4 The gross sectional appearance, microstructure, vasculature and ultrastructure of the suprarenal gland. Brief functional summaries are included.

Superior suprarenal arteries

The superior suprarenal artery arises from the inferior phrenic artery, a branch of the abdominal aorta: it is often small and may be absent.

Middle suprarenal arteries

The middle suprarenal artery arises from the lateral aspect of the abdominal aorta at the level of the superior mesenteric artery. It ascends slightly and runs over the crura of the diaphragm to the suprarenal glands, where it anastomoses with the suprarenal branches of the inferior phrenic and renal arteries. The right middle suprarenal artery passes behind the inferior vena cava and near the right coeliac ganglion and is frequently multiple. The left middle suprarenal artery passes close to the left coeliac ganglion, splenic artery and the superior border of the pancreas.

Inferior suprarenal arteries

The inferior suprarenal arteries arise from the renal arteries, usually from the main renal artery but occasionally from its upper pole branches.

Veins

Medullary veins emerge from the hilum to form a suprarenal vein, which is usually single. The right vein is very short, passing directly and horizontally into the posterior aspect of the inferior vena cava. An accessory vein is occasionally present and runs from the hilum superomedially to join the inferior vena cava above the right suprarenal vein. Their short course renders both right vessels liable to injury or even avulsion from the inferior vena cava during surgery if undue traction is applied, producing a side hole in the cava. The left suprarenal vein descends medially, anterior and lateral to the left coeliac ganglion. It passes posterior to the pancreatic body and drains into the left renal vein. Since the venous drainage from each gland is usually via a single vein, infarction of that gland is more likely to be caused by damage to a suprarenal vein than to one of the suprarenal arteries.

Lymphatic drainage

Small lymphatic channels from both cortex and medulla drain to the hilum, from where larger calibre lymphatics emerge to drain directly into the lateral groups of para-aortic nodes.

INNERVATION: SUPRARENAL PLEXUS

The suprarenal gland, relative to its size, has a larger autonomic supply than any other organ. On each side, the suprarenal plexus lies between the medial aspect of the gland and the coeliac and aorticorenal ganglia. It contains mostly preganglionic sympathetic fibres, which originate in the lower thoracic spinal segments and which reach the plexus via branches from the coeliac ganglion and plexus, and via the greater splanchnic nerve. These fibres synapse, often in deep invaginations, on large medullary chromaffin cells, which may therefore be considered to be homologous with postganglionic sympathetic neurones. A preponderance of non-myelinated axons has been described in the human suprarenal plexus. Both cortex and medulla also contain acetylcholinesterase (AChE)-positive axons that presumably reach the gland from the coeliac plexus: some synapse with ganglion cells in the zonae fasciculata and reticularis.

MICROSTRUCTURE

In section, the suprarenal gland has an outer cortex, which is yellowish in colour and forms the main mass, and a thin medulla, forming about one-tenth of the gland, which is dark red or greyish, depending on its content of blood (see Figs 72.4, 72.5). The medulla is completely enclosed by cortex, except at the hilum. The gland has a thick collagenous capsule from which trabeculae extend deep into the cortex. The capsule contains a rich arterial plexus which supplies branches to the gland.

Fig. 72.5 Cross section through an adult suprarenal gland showing the zona granulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR), and the highly vascular medulla (M).

(By courtesy of Mr Peter Helliwell and Dr Joseph Mathew, Department of Histopathology, Royal Cornwall Hospitals Trust, UK.)

SUPRARENAL GLAND EXCISION

Removal of one or both suprarenal glands may be performed either through ‘open surgery’ or via a laparoscopic approach. There are essentially three ‘open surgical’ methods for removing the suprarenal glands. The posterior and lateral approaches involve removal of either the eleventh or twelfth ribs. The surgeon remains in the retroperitoneal plane and accesses the gland via the perirenal fat. This approach can be performed laparoscopically, but is difficult: landmarks are not easily identified because of the surrounding fat and the ‘workspace’ is frequently small. Not surprisingly, few surgeons employ this approach.

During laparoscopic surgery the anterior, transperitoneal approach is most commonly used. The patient is placed in the lateral decubitus position. On the left side, the splenic flexure is mobilized inferiorly, revealing the kidney. The lateral phrenicocolic ligament is then fully divided, which allows the spleen to be mobilized medially exposing the splenorenal ligament. Division of the splenorenal ligament (when the patient is in the lateral decubitus position) allows the spleen to ‘drop’ medially. This exposes the plane between the splenic hilum and medial border of the left kidney, and is where the pancreatic tail is identified as it runs to the hilum of the spleen. The renal fascia is divided to expose the suprarenal gland lying over the superomedial aspect of the upper pole of the kidney. On the right side, the right triangular ligament of the liver is divided, which allows the liver to be retracted caudally. In most individuals the inferior vena cava is easily identified behind the peritoneum lateral to the second part of the duodenum. The peritoneal reflection on the inferior border of the liver is divided from the inferior vena cava to the lateral border of the liver, exposing the suprarenal gland in the angle between the inferior vena cava and liver. The peritoneal reflection along the lateral aspect of the inferior vena cava is divided and the gland is then mobilized laterally exposing the suprarenal vein, which often emerges from the posterior aspect of the inferior vena cava. Once the suprarenal vein has been divided, the small middle suprarenal arteries, which run from the aorta to the gland behind the inferior vena cava, are easily identified. The gland is then usually mobilized very easily in a lateral direction. However, it can lie either behind the inferior vena cava or under the liver, in which case dissection at the junction of the liver and inferior vena cava often becomes very difficult.

In obese (or Cushingoid) patients, identification of a relatively normal sized suprarenal gland can be extremely difficult and time consuming. The suprarenal vein emerges from the lower medial border of the gland and it is often a very substantial structure. In contrast, the supplying arteries tend to be rather smaller in size and individual arteries are often difficult to identify during surgery.

The anterior open approach follows the procedure as described above through either a subcostal or a midline incision.