Surface anatomy of head and neck region

 Surface anatomy of head and neck region 

Skull : cranium with mandible is know as skull 

Cranium : skull without mandible is know as cranium 

Bony prominence of skull 

 The external occipital protuberance is a raised area on the midline of the occipital bone where the posterior wall meets the base of the skull. It is medial to the two superior nuchal lines. It is at the superior extent of the ligamentum nuchae that connects the cervical vertebrae to the skull

 

 

Inion: Is the highest point on the external occipital proturberance. Deep to it lies the confluence of the dural venous sinuses at the crux between the cerebral and cerebellar hemispheres.

Lambda: It corresponds to a slightly depressed area about 7 cm above and in front of the external occipital protuberance.

Bregma: It corresponds to the middle point of a line joining the external acoustic meatuses of the two sides across the vertex. It is the meeting point of the sagittal and coronal sutures of the skull.

Nasion:

It is a well marked depression at the root of the nose and is the meeting point of the fronto-nasal and internasal sutures.

Pterion:

This is a small circular area where the frontal, sphenoid, parietal and temporal sutures meet. Its centre can be located about 3.5 cm behind the frontozygomatic suture and 4 cm above the zygomatic arch. Its position can be roughly estimated by a shallow palpable hollow, about 3.5 cm above the centre of the zygomatic arch. Pterion marks the anterior branch of middle meningeal artery and the Sylvian point of the brain.

Asterion:

It corresponds to a point 4 cm behind the external acoustic meatus and 1.25 cm above a line joing the external acoustic meatus and the inion (meato-inionic line).

Gonion (angle of the mandible): 

It can be seen and palpated below and in front of the lobule of the ear

 

 Reid’s base line:

It is represented by a horizontal line which extends posteriorly from the lowest point of the infra-orbital margin through the centre of the external acoustic meatus.

The cerebrum lies entirely above this line, whereas the cerebellum occupies the area immediately below the posterior third of this line.

Horizontal views (sections) of C.T. scan or M.R.I. of the brain are made by superimposed lines parallel to the Reid’s base line to represent the levels of images.

Frankfurt’s plane : it is almost identical with Reid’s base line, except that the posterior point passes through the upper margin of the external acoustic meatus. This plane is accepted by the physical anthropologists as the standard orientation of the human skulls for the study of characteristics of different races.

 

Supra-meatal triangle:

It is a small trian­gular depression of temporal bone, bounded above by the supramastoid crest, in front by the postero- superior margin of external acoustic meatus, and behind by the posterior vertical tangent to the meatal margin.

This triangle represents the lateral wall of the mastoid (tympanic) antrum, which lies about 2 cm deep to the triangle in adult, but only 2 mm deep in the new-born.