Where is the glabella located and what are its boundaries?
The glabella (glabella) is located on the external surface of the skull (facies externa) in the midline, directly above the root of the nose.
- The inferior boundary of the external surface in this area is the supraorbital margin (margo supraorbitalis).
- Adjacent structures: closer to the glabella in the medial half of the supraorbital margin, the frontal notch or supraorbital foramen (incisura frontalis / foramen frontale) may be present. The supratrochlear vessels and nerve (a., v. et n. supratrochlearis) pass through them.
- Venous system: a single or double frontal vein is located in the midline superior to the glabella. Arteries typically do not pass here, and the veins of the cranial vault lack valves.
Furthermore, the glabella, together with the supraorbital margin of the frontal bone, serves as the anterior boundary of the frontoparietooccipital region, which combines the first three unpaired regions of the cranial vault.
What is its role in craniocerebral topography?
The glabella is used as a landmark when constructing the craniocerebral topography diagram (Krölein's scheme), which allows the projection of the main cerebral sulci and the course of the middle meningeal artery onto the skull.
- Median sagittal line: constructed by drawing a line from the glabella (glabella) to the external occipital protuberance (protuberantia occipitalis externa).
- Projection of the dura mater: the superior edge of the falx cerebri (falx cerebri) — a fold of the dura mater separating the cerebral hemispheres — is projected onto this same sagittal line. The dura mater folds act as shock absorbers protecting the brain from concussions and injuries.
What is its clinical significance in obstetrics?
In obstetrics, the glabella is the leading point in brow presentation of the fetal head. Extension presentations occur with a frequency of 0.5–1%.
- Leading point: glabella is the leading point in brow presentation.
- Biomechanism: in this presentation, the fetal head passes through the pelvic planes with its largest dimension — the mentookcipital diameter (long oblique diameter). Its diameter is 13.5 cm, and its circumference is 41–42 cm. Extension of the head occurs in the plane of the pelvic inlet, and internal rotation with the formation of a persistent occipito-posterior position occurs in the broad part of the pelvic cavity.
- Prognosis: brow presentation is considered the most unfavorable option. It leads to significant labor dystocia, and vaginal delivery is possible only with a very low fetal birth weight.
- Dynamics: the presentation is unstable. With further extension during labor, a brow presentation may convert to a face presentation, where the chin becomes the leading point. Persistent extension presentations are rare and associated with pathologies such as a large goiter or extensive cystic hygroma of the fetal neck, or large submucosal uterine myomas in the mother.
Class and exam questions
What runs near the glabella?
Closer to the glabella in the medial part of the supraorbital margin is the frontal notch or foramen, through which the supratrochlear nerve and vessels pass. Superior to the glabella itself in the midline runs the frontal vein.
Which line uses the glabella for its construction in Krölein's scheme?
The glabella serves as the starting point for constructing the median sagittal line, which terminates at the external occipital protuberance. The superior edge of the falx cerebri is projected onto it.
What are the risks of fetal brow presentation?
In brow presentation, where the glabella is the leading point, the head passes through the pelvic planes with its largest dimension — the long oblique diameter — measuring 13.5 cm. Brow presentation leads to significant labor dystocia, and vaginal delivery is possible only with a very low fetal birth weight.
What else to study on this topic
- Frontal bone and supraorbital margin
- Krönlein's craniometric scheme
- Extension presentations of the fetal head
- Frontoparietooccipital region
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