Location of the Foramen Ovale
The foramen ovale is located on the internal skull base, specifically within the middle cranial fossa (fossa cranii media). Topographically, it belongs to the greater wing of the sphenoid bone.
The foramen serves as an important passageway, connecting the cranial cavity to the external skull base (basis cranii externa). The external skull base leads directly into the infratemporal fossa (fossa infratemporalis). Spatially, on the external skull base, it lies posterior to the lateral plate of the pterygoid process of the sphenoid bone.
Contents of the Foramen Ovale
Structures of the trigeminal nerve (CN V) exit the cranial cavity through this foramen:
- Mandibular nerve (n. mandibularis) — the third division of the trigeminal nerve. It is a mixed nerve trunk containing sensory and motor fibers, with sensory branches making up the majority of the nerve.
- Motor root of the trigeminal nerve (portio minor) — exits the skull alongside the mandibular nerve. It originates from the motor nucleus in the pontine tegmentum and provides innervation to the muscles of mastication (masseter, temporalis, medial and lateral pterygoids), as well as the mylohyoid, anterior belly of the digastric, and tensor tympani muscles.
Clinical Significance: Regional Anesthesia
In dental and maxillofacial surgery, the foramen ovale serves as a landmark for regional nerve blocks of the mandibular nerve. This type of anesthesia is indicated for extensive surgical procedures requiring pain control across the entire lower jaw.
According to classical anatomical landmarks (such as Weissblatt's technique), the primary bony reference point is the lateral plate of the pterygoid process. The foramen ovale lies in the same plane as this plate, but is positioned posterior to it. A 7–8 cm needle is typically utilized for this nerve block approach.
Distinction: Foramen Ovale of the Heart
In anatomy, the term foramen ovale cordis is also used to describe a structure in the fetal cardiovascular system.
- Prenatal period: This is a valved opening in the interatrial septum (septum interatriale). It functions as a right-to-left shunt, directing oxygenated blood from the inferior vena cava through the right atrium into the left atrium, bypassing the pulmonary circulation.
- After birth: Left atrial pressure exceeds right atrial pressure by 6–8 times. The valve flap closes, preventing left-to-right blood flow. Closure typically occurs within the first 3 months of life, occasionally taking 1–2 years. The remnant on the septum forms the fossa ovalis.
- Pathology: If the opening remains inappropriately large (patent foramen ovale or septal defect), the flap fails to prevent shunting. This results in an acyanotic congenital heart defect with left-to-right blood flow, leading to right heart enlargement and pulmonary artery dilation, while the left ventricle remains unaffected.