Sella Turcica: Structure, Function & Diseases

As part of the os sphenoidale, the sella turcica forms a bony structure at the base of the skull. Within the saddle-shaped depression sits the pituitary gland, which is connected to the thalamus via the pituitary stalk. Hormonal processes in the human body are controlled from here.

What is the sella turcica?

The term “sella turcica” is composed of the Latin words for “seat” and “Turkish”. In German, the term “Türkensattel” is also used synonymously. The sella turcica is a bony prominence of the os sphenoidale (sphenoid bone) at the inner base of the skull. It divides the middle cranial fossa in the medial plane into right and left halves. It was named after the Belgian anatomist and professor of anatomy and surgery Adriaan van den Spieghel (1578 – 1625). He compared the indentation of this bone structure to a saddle with a high back, such as the Turks used to use. The sella turcica is the only structure in the human body named after an entire people. Van den Spieghel first coined the term Turk’s saddle in his work “De humani corporis fabrica libri decem”, published in 1627. A detailed discussion of the term “sella turcica” can be found in the work of the Austrian anatomist Joseph Hyrtl (1810 – 1894). He discusses it in his works “Onomatologia Anatomica” and “The Arabic and Hebrew in Anatomy”.

Anatomy and structure

Anatomically, the sella turcica is assigned to the os sphenoidale. This cranial bone lies frontal to the ossa temporalia and the os occipitale at the base of the skull. It can be divided into a body (corpus ossis sphenoidalis) and two wings (alae majores and minores) and the posteriorly projecting processus pterygoidei. This bone is the most complex in the human body and is also called the wasp bone because of its shape. The sella turcica is located on the upper side of the os sphenoidale. On two sides, the elevations characteristic of the turcic saddle can be seen. Anteriorly, this is the tuberculum sellae (the saddle button) with two lateral bumps, the processus clinoidei anteriores. The dorsal border is formed by the dorsum sellae (the saddle bone) with the processus clinoidei posteriores. Between these two projections lies a pit open to the brain, the hypophysial fossa. This is where the pituitary gland (hypophysis) is located. The sella turcica is spanned by a portion of the dura mater called the diaphragma sellae. This separates the pituitary gland from the basal parts of the brain as well as the optic nerve junction.

Function and tasks

The sella turcica is a bony structure. As such, it is part of the passive musculoskeletal system, which includes approximately 200 bones. As part of the os sphenoidale, the sella turcica is an unpaired, irregular bone. Due to their complicated structure, these cannot be assigned to any other bone shapes. The human skull is the result of a long evolution, which shaped the body in an efficient way. As an irregular bone, the Os sphenoidale has a supporting and protective function. It is also involved in shaping the skull. Unlike most other bones of the human body, the Os sphenoidale does not form an origin or attachment point of one or more muscles. Like any bone, the Os sphenoidale contains marrow and thus has a metabolic function. Two types of bone marrow are distinguished: red and white. The function of the red bone marrow is to form undifferentiated stem cells. It is referred to as hematopoietic bone marrow. Erythrocytes, platelets and leukocytes are produced there. The white bone marrow, also known as fat marrow, serves as an energy store. When there is a large loss of blood, white bone marrow is converted into red bone marrow. This process is called hematopoiesis. In infants, red marrow is found in all the bones of the body; in adulthood, it is found only in the flat and short bones. The sella turcica, as part of the os sphenoidale, houses the pituitary gland. As the interface between the nervous system and hormonal balance, metabolism, growth, and the function of other endocrine organs are controlled here, among other things.

Diseases

The pituitary gland is protected by the bony structure of the sella turcica. Nevertheless, changes in the tissue or disease can occur at this site. Tumors in the area of the pituitary gland are often only detected after years.Among other things, those affected suffer from nausea, loss of performance, metabolic disorders or headaches. In addition, visual field defects may occur if the optic nerve is involved. In this case, an ophthalmologic examination of the visual field is necessary in addition to imaging diagnostics. Most pituitary tumors can be surgically removed through the nose. If the pituitary gland is not visible on computer or magnetic resonance imaging scans, an empty sella syndrome or syndrome is present. The reason is usually an outpouching of the meninges into the sella turcica. This protrusion presses the pituitary gland to the edge of the sella, giving the impression of an empty sella in imaging studies. Another cause may be damage to the pituitary tissue from infarcts, surgery, or radiation. If the affected individual shows no clinic, no further testing is necessary. Empty Sella Syndrome may manifest as headaches, constant runny nose, and visual disturbances, among other symptoms. More rarely, there is an overproduction of the neurotransmitter prolactin. This leads to a milky secretion from the breast, disturbances of the menstrual cycle, potency disorders and infertility. Symptoms can be treated surgically or with medication, depending on the cause.