Introduction
The kidneys are a pair of excretory organs situated in the retroperitoneal area (the space in the abdominal cavity behind the peritoneum is called the retroperitoneal space). The kidneys are usually the size of one’s fists, and a male kidney is found to be larger than a female’s kidney. They are bean-shaped, with a concavity on one side and a convexity on the other. They are located between the twelfth thoracic and the third lumbar vertebrae. The functions of the kidney include the regulation of blood pressure, the production of hormones like calcitriol and erythropoietin, and maintaining the pH of the blood. They are considered to be the powerful chemical factories of the body.
What Is Hilum of Kidney?
The hilum of the kidney is a vertical aperture seen on the medial surface. It provides an opening for the nerves, lymphatics, blood vessels, and ureter to enter. A hilum is a general term meaning a depression that allows the passage of structures. The hilum of the kidney is covered by the thick lips of the renal parenchyma. It is lined by the renal capsule. The renal capsule is a tough connective tissue that covers the kidneys. The renal vessels, nerves, lymphatics, and the renal pelvis pass through the renal hilum. The hilum usually faces anteriorly at birth. The hilum rotates medially at a right angle as the kidney ascends from the pelvis anteriorly.
What Is the Anatomical Location of the Hilum of the Kidney?
The hilum of the kidney lies below the transpyloric plane on the right side. On the other hand, it lies just above the transpyloric lane. An imaginary horizontal plane midway between the lower border of the body of the sternum and the umbilicus is called the transpyloric plane (also called Addison’s plane). The hilum of the kidneys connects with the renal sinus inside the kidney. A hilum is a depression that allows the passage of various structures in general. The renal sinus is a protective layer of the kidney that protects the important parts of the kidney. It is usually made of fat.
What Are the Structures Leaving or Entering the Hilum of the Kidney?
The structure that enters or leaves the hilum of the kidney is the renal vein, the renal artery, and the renal pelvis (a large cavity that collects the urine that is produced is called the renal pelvis). A corresponding tributary of the renal vein, along with a branch of the renal artery usually passes behind the renal pelvis. Studies show that in about seventy percent of people, the kidney is supplied by one renal artery. However, in the rest of the population, one or more renal arteries may supply the kidney. Multiple arteries supplying the kidney may be present in a normally functioning kidney, though it is common in congenitally malformed or abnormally positioned kidneys. Accessory renal arteries also enter the kidney through the hilum. The renal arteries usually branch at the hilum. On the other hand, five to six tributaries of the renal vein unite at or near the hilum to form a single renal vein. The renal vein is drained into the inferior vena cava (the inferior vena cava carries deoxygenated blood from the lower body parts to the heart). Since the inferior vena cava is located more towards the right, the renal vein on the left side is usually longer than the right. The left renal vein may also divide into two- one passes anteriorly and the other posterior to reach the aorta, and eventually drain into the inferior vena cava. The posteriormost space is occupied by the renal pelvis.
The position of the renal pelvis may vary from person to person. For some people, it might be fully inside the renal sinus. On the other hand, some people might have split their ureter and pelvis. The early splitting of the ureteric bud during the embryonic stage is thought to be the reason behind this.
What Is the Clinical Significance of the Hilum of Kidney?
The knowledge of the anatomy of the hilum and the structures passing through it is important in doing various surgical procedures related to the kidney or urological procedures like laparoscopic nephrectomies, atrophic nephrolithotomy, or kidney transplantations. Clamping of the hilar vessels is important in such procedures. The knowledge of the branching patterns of the renal blood vessels in and around the hilum of the kidney, along with awareness of its variation is essential in performing surgical procedures related to the kidney. The awareness of the variations in anatomy is important in performing various invasive procedures and reducing vascular complications.
The variations in the branching pattern can be challenging for radiologists as well. This is especially true for radiologists who interpret renal angiograms. A renal angiogram is done to know about the blood vessels of the kidneys. This can also be a complicated scenario for urologists who perform laparoscopic surgeries. With an increase in kidney and related diseases, there has been an increased requirement for kidney transplantations. The variations in the branching patterns of the renal vessels play an important role in deciding a suitable graft.
Conclusion
The hilum of the kidneys is a slit found in the medial aspect of the kidney. It is covered by the renal capsule and provides an opening for the various structures entering and leaving the kidney. The kidneys are a paired organ, which helps in the excretory process. The hilum of the kidney is a small area, yet of profound importance, especially in the invasive procedures related to the organ. A profound and thorough knowledge of the anatomy of the hilum and the structures passing through it, along with the possible anatomic variations, is necessary to prevent any mishaps during a renal procedure. It is also important for determining the success rate of the procedure and preventing any complications. Another area where it might be useful is in reading a renal angiogram. A renal angiogram provides information on the blood vessels supplying the kidneys.
