What is the Difference Between Fossa and Foramen

The main difference between fossa and foramen is that the fossa is a shallow depression in the bone surface, whereas the foramen is a hole through which nerves and blood vessels pass.

Fossa and foramen are two common bone markings that are valuable for identifying individual bones. They are important for clinicians and surgeons.     

Key Areas Covered

1. What is Fossa
– Definition, Anatomy, Function
2. What is Foramen
– Definition, Anatomy, Function
3. Similarities Between Fossa and Foramen
– Outline of Common Features
4. Difference Between Fossa and Foramen
– Comparison of Key Differences

Key Terms 

Foramen, Fossa

What is Fossa

Fossa is a shallow depression occurring on the surface of the bone. Often, it receives another articulating bone. Sometimes, it supports the structures of the brain. Examples of the fossa are the trochlear fossa and the posterior, middle, and anterior cranial fossa. The trochlear fossa is a slight depression on the anteromedial orbital surface of the orbital plate of the frontal lobe in the human skull. The Trochlear is the muscle that attaches to the trochlear fossa. Also, it is a part of the superior oblique muscle. Other fossae in the skull include cranial fossa, hypophyseal fossa, temporal bone fossa, infratemporal fossa, etc.

Figure 1: Throchlea Fossa

Furthermore, the three types of cranial fossa include anterior cranial fossa, middle cranial fossa, and posterior cranial fossa. The floor of the cranial cavity forms the cranial fossa. The anterior cranial fossa houses the projecting frontal lobes of the brain. Also, the middle cranial fossa houses the temporal lobe. The clivus and the petrous crest separate it from the posterior cranial fossa. Meanwhile, the posterior cranial fossa houses the brainstem and cerebellum. It occurs between the foramen magnum and tentorium cerebelli. Apart from the skull, fossae also occur in other bones, including the mandible, torso, and upper and lower limbs. 

What is Foramen

Foramen is a hole in bones through which nerves and blood vessels pass. For example, the skull contains numerous foramina that transit blood vessels, cranial nerves, and other structures. Collectively, the foramina in the skull are called cranial foramina. They include the optic canal, superior orbital fissure, foramen rotundum, foramen ovale, internal acoustic meatus, jugular foramen, and hypoglossal canal -CN XII. Here, the optic canal allows the passage of the ophthalmic artery and optic nerve (CN II) into the bony orbit. It attaches medially to the body of the sphenoid and laterally to the lesser wing of the sphenoid bone. Also, the superior orbital fissure is an aperture that opens anteriorly into the orbit. It allows communication between the apex of the orbit and the cavernous sinus. Also, it transmits the lacrimal nerve, frontal nerve, superior ophthalmic nerve, trochlear nerve, etc.

Figure 2: Cranial Foramen

Moreover, the foramen rotundum occurs at the base of the greater wing of the sphenoid. Also, it occurs inferior to the superior orbital fissure. It passes the maxillary nerve, connecting the middle cranial fossa and the pterygopalatine fossa. Further, the foramen ovale passes the mandibular nerve and the accessory meningeal artery. However, internal acoustic meatus passes the vestibular ganglion, labyrinthine artery, and facial and vestibulocochlear nerves. In addition, the jugular foramen posteriorly transmits meningeal branches of occipital and ascending pharyngeal arteries. Also, it medially transmits the glossopharyngeal nerve, vagus nerve, and cranial part of the accessory nerve. On the other hand, the hypoglossal canal transmits the hypoglossal nerve (CN XII). 

Similarities Between Fossa and Foramen

• Fossa and foramen are two common bone markings.
• They are important for the identification of bones.
• Also they are used by clinicians and surgeons. 

Difference Between Fossa and Foramen

Definition

Fossa refers to an anatomical pit, groove, or depression. In contrast, foramen refers to an opening, hole, or passage, especially in a bone.

Type of Bone Mark

Fossa is a shallow depression in the bone surface, while the foramen is a hole through which nerves and blood vessels pass. 

Examples

Examples of fossa are trochlear fossa, posterior, middle, and anterior cranial fossa, while examples of foramen are supraorbital foramen, infraorbital foramen, and mental foramen on the cranium.

Conclusion

In brief, fossa and foramen are common bone markings on bones. They are important for the identification of individual bones. Fossa is a shallow depression on the surface of the bone. The trochlear fossa, posterior, middle, and anterior cranial fossa are examples of fossa. In comparison, the foramen is a hole. Nerves and blood vessels pass through it. Supraorbital foramen, infraorbital foramen, and mental foramen on the cranium are the examples of foramen. Therefore, the main difference between fossa and foramen is their structure. 

References:

1. Bandovic I, Holme MR, Black AC, et al. Anatomy, Bone Markings. [Updated 2022 Dec 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-

Image Courtesy:

1. “Slide10DEN” By Anatomist90 – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Slide6gre.” By Anatomist90 – Own Work (CC-BY SA 3.0) via Commons Wikimedia