Variants and anomalies of cranial bone development

Variants and anomalies in the development of the bones of the skull are quite common.

Frontal bone. In about 10% of cases, the frontal bone consists of two parts, with the frontal suture (sutura frontalis, s. sutura metopica) remaining between them. The size of the frontal sinus varies, and the sinus is very rarely absent.

Sphenoid bone. Non-union of the anterior and posterior halves of the body of the sphenoid bone leads to the formation of a narrow, so-called craniopharyngeal canal in the center of the sella turcica. The oval and spinous openings sometimes merge into one common opening; the spinous opening may be absent.

Occipital bone. The upper part of the occipital squama can be separated entirely or partially from the rest of the occipital bone by a transverse suture. As a result, a special triangular bone is distinguished - the interparietal bone (os interparietale). Assimilation of the atlas, i.e. complete or partial fusion of the occipital condyles with the first cervical vertebra, is rare. Near the occipital bone there are often additional bones (bones of the sutures, ossa suturalia). Sometimes the external occipital protuberance reaches significant dimensions. There is also a third occipital condyle, located at the anterior edge of the large (occipital) foramen. It articulates with the anterior arch of the atlas by means of an additional joint.

Ethmoid bone. The shape and size of the ethmoid bone cells are very variable. The highest nasal concha (concha nasdlis suprema) is often found.

Parietal bone. Because the ossification points do not fuse, each parietal bone may consist of an upper and lower half.

Temporal bone. The jugular notch of the temporal bone can be divided into two parts by the interjugular process. If there is a similar process in the jugular notch of the occipital bone, a double jugular opening is formed. The styloid process of the temporal bone may be absent, but is often long, and can even reach the hyoid bone with ossification of the stylohyoid ligament.

Upper jaw. The number and shape of dental alveoli are different and often there is an unpaired incisor bone, which is typical for mammals. On the lower surface of the bony palate, a ridge is sometimes formed along the midline. The incisive canal and sinuses of the upper jaw can vary in size and shape. The most severe malformation of the upper jaw is a cleft hard palate - "cleft palate", or more precisely, a failure to fuse the palatine processes of the maxillary bones and the horizontal plates of the palatine bones.

Zygomatic bone. A horizontal suture may divide the bone in half. A variable number of canals penetrating the bone are also observed.

Nasal bone. The shape and size are individual, sometimes the bone is absent, being replaced by the frontal process of the upper jaw. Often the nasal bones are located asymmetrically or grow together and form one common nasal bone.

Lacrimal bone. The size and shape of this bone are variable. Sometimes the absence of the lacrimal bone is compensated by an enlarged frontal process of the maxilla or the orbital plate of the ethmoid bone.

Inferior nasal concha. The bone often varies in shape and size, especially its processes.

Ploughshare. Can be curved to the right or left.

Lower jaw. The right and left halves of the body are often asymmetrical. The dimensions of the angle between the body of the lower jaw and its branch are individual. There is a duplication of the mental opening and the opening of the lower jaw, as well as the canal of the lower jaw.

Hyoid bone. The size of the body of the hyoid bone, the greater and lesser horns is not constant.