Table 2.
Landmarks, lines and measurements
| Measurement | Notation | Description |
|---|---|---|
| Landmarks | ||
| Orbital inferior | Oi | point of orbital margin closest to the toothrow |
| Orbital superior | Os | point of the orbital margin furthest from the toothrow |
| Orbital medial | Om | point on the orbital margin closest to the junction between the frontonasal and internasal sutures |
| Orbital lateral | Ol | point on the orbital margin furthest from the junction between the frontonasal and internasal sutures |
| Optic canal | Oc | point marking the centre of the opening of the optic canal into the orbit |
| Anterior lateral canal | LSCa | centre of lumen of the anterior limb of the lateral canal at its widest point |
| Posterior lateral canal | LSCp | centre of lumen of the posterior limb of the lateral canal at its widest point |
| Basion | Ba | The midline point on the anterior margin of the foramen magnum |
| Foramen caecum | Fc | The midline point marking the pit between the fetal crista galli and the endocranial wall of the frontal bone |
| Pituitary point | Pp | The midline point on the raised tuberculum sella of the body of the sphenoid. |
| Anterior nasal margin | ANM | The midline point marking the intersect between the rostral most tip of the nasal septum and the surface of the maxilla |
| Posterior nasal spine | PNS | The midline point on the tip of the posterior nasal spine |
| Hormion | H | The posterior-most midline point on the junction between the ventral surface of the sphenoid and the vomeral root |
| Pterygomaxillare | Ptm | the junction between the medial and lateral pteryoids and maxilla |
| Lines | ||
| Midsagittal line | MSP | Line passing through Fc, Pp and Ba and projected onto the transverse plane of the skull |
| Lateral canal line | LCP | Line passing through the anterior and posterior limbs of the lateral semicircular canal (LSCa-LSCp) and projected onto the sagittal plane of the skull |
| Angles (°) | ||
| Angle of orbital margin convergence | AOMc | Angle of a line passing through the medial most (Om) and lateral-most (Ol) margins of the orbit against the midsagittal plane |
| Angle of orbital axis convergence | AOAc | Angle of a line passing through the centroid of all orbital margin landmarks (Os, Oi, Ol and Om) and the optic canal (OC) against the midsagittal plane |
| Angle of orbital margin frontation | AOMf | Angle of a line passing through the inferior-most (Oi) and superior-most (Os) margins of the orbit against the lateral canal plane |
| Angle of orbital axis frontation | AOAf | Angle of a line passing through the centroid of all orbital margin landmarks (Os, Oi, Ol and Om) and the optic canal (OC) against the lateral canal plane |
| Angle of facial projection | AFP | Angle of a line passing through the foramen caecum (Fc) and the anterior nasal margin (ANM) against the lateral canal plane |
| Cranial base angle | CBA | Angle between lines passing through foramen caecum (Fc), pituitary point (Pp) and basion (Ba) |
| Lengths, areas and volumes | ||
| Skull height | Sh | Maximum distance in the midline from the base of the basisphenoid to the top of the cranial vault |
| Skull width | Sw | Distance marking the widest distance in the axial plane. |
| Skull length | Sl | Maximum distance in the midline from nasion to opisthocranion |
| Cranial base length (mm) | TBL | Total distance from foramen caecum (Fc) to pituitary point (Pp) to basion (Ba) |
| Anterior base length (mm) | ABL | Distance from foramen caecum (Fc) to pituitary point (Pp) |
| Posterior base length (mm) | PBL | Distance from pituitary point (Pp) to basion (Ba) |
| Skull volume (mm3) | SKV | Multiple of skull height, width and length |
| Nasal septum area (mm2) | NSA | Area of the cartilaginous mesethmoid (nasal septum plus perpendicular plate of ethmoid) taken from the midsagittal slice. |
| Eye ball volume (mm3) | EBV | Summated outlined areas of both eyeballs taken in transverse slices |
| Endocranial volume (mm3) | EV | Summated outlined areas of the endocranial cavity taken in sagittal slices |
| Supratentorial volume (mm3) | SV | Summated outlined areas of the endocranial cavity above the tentorium cerebelli taken in sagittal slices |
| Infratentorial volume (mm3) | IV | Summated outlined areas of the endocranial cavity below the tentorium cerebelli taken in sagittal slices |
| Relative sizes | ||
| Index of relative endocranial volume | IRE | Cube root of endocranial volume (EV) divided by the length of the cranial base (TBL) |
| Index of relative supratentorial volume | RSE | Cube root of the supratentorial volume (SV) divided by the length of the anterior cranial base (ABL) |
| Index of relative infratentorial volume | RIE | Cube root of the infratentorial volume (IV) divided by the length of the posterior cranial base (PBL) |
| Index of relative eye volume | IRO | Eye volume (EBV) divided by skull volume (SKV) |
| Index of relative endocranial and eye volume i | IREOi | Cube root of eye (EBV) plus cube root endocranial volume (EV) divided by cube root skull volume (SKV) |
| Index of relative endocranial and eye volume ii | IREOii | Cube root of eye (EBV) plus cube root endocranial volume (EV) divided by cranial base length (TBL) |
| Index of relative nasal septal size I | IRNi | Square root of nasal septum area (NSA) divided by cube root skull volume (SKV) |
| Index of relative nasal septal size ii | IRNii | Square root of nasal septum area (NSA) divided by cranial base length (TBL) |
| Index of relative nasal septal size iii | IRNiii | Square root of nasal septum area (NSA) divided by anterior cranial base length (ABL) |
| Index of relative soft-tissue size I | IRSTi | cube root of endocranial volume (EC) plus cube root of eye volume (EBV) plus sqaure root of septum area (NSA) divided by cube root skull volume (SKV) |
| Index of relative soft-tissue size ii | IRSTii | cube root of endocranial volume (EC) plus cube root of eye volume (EBV) plus sqaure root of septum area (NSA) divided by cranial base length (TBL) |