The cranial fossa media is the middle cranial fossa that contains the temporal or temporal lobe of the cerebrum. Its shape resembles that of a butterfly. The cranial fossa media also has several openings through which cranial nerves and blood vessels access the brain.
What is the cranial fossa media?
The human brain lies within a bony cranial cavity that provides protection and a dimensionally stable shell for the delicate organ. The cranial fossa media corresponds to the middle cranial fossa. It is located between the anterior cranial fossa, which lies beneath the frontal lobe of the brain, and the posterior cranial fossa, which is the rearmost of the three cranial fossae. All three belong to the base of the skull (basis cranii), which, together with the skullcap (calvaria), forms the cranium. Viewed from above, the shape of the fossa cranii media is reminiscent of a butterfly symmetrically mirrored along the long axis of the skull. The middle cranial fossa supports the temporal lobe or temporal lobe of the cerebrum (lobus temporalis). Its convolutions (gyri) and folds (sulci) map the cranial bones as impressiones digitatae and juga cerebralia.
Anatomy and structure
At the boundary between the middle and anterior cranial fossae is the lesser sphenoid wing (ala minor ossis sphenoidalis), which encloses the fossa cranii media in a convex arch. Posteriorly, the middle cranial fossa terminates at an edge of the petrous bone (pars petrosa ossis temporalis). The “floor” of the middle cranial fossa is composed of several cranial bones: the greater sphenoid wing (Ala major ossis sphenoidalis), the parietal bone (Os parietale), the temporal bone scale (Pars squamosa ossis temporalis or Squamosa temporalis), and the surface of the petrous bone. There are several openings in and between the bones. These include the superior orbital fissure (fissura orbitalis superior), which connects to the orbit. Also leading to the orbit is the optic canal (canalis opticus), which is 5-10 mm long. With a size of 20 x 6 mm, the opening is relatively large. The foramen ovale in the sphenoid bone has a regular roundish shape and is slightly smaller at 4-5 x 7-8 mm. In contrast, the foramen lacerum has irregular margins and lies between the sphenoid bone, temporal bone, and occipital bone. The foramen spinosum and the foramen rotundum represent other penetration sites in the fossa cranii media and have a round shape.
Function and Tasks
The function of the cranial fossa media is to provide protection to the portion of the brain that overlies it. Part of the temporal lobe is represented by the hippocampus, which plays an important role in memory. Other structures in the temporal lobe, such as the entorhinal cortex and the parahippocampal and perirhinal areas, are also critical for memory. The Wernicke center is part of the language center and is used for language comprehension. It corresponds to Brodman area A 22. In addition, the temporal lobe houses the primary auditory cortex, which processes auditory percepts and delivers nerve fibers to the internal capsula. The so-called neocortical associative areas in the temporal lobe deal with complex auditory, but also visual information. Parts of the temporal lobe can also be grouped into the limbic system. This is a system of various brain structures that are involved in the development of emotions, memory functions and sexual functions, among other things. The limbic system is considered to be very old in terms of developmental history. It includes the hippocampus, the amygdala (corpus amygdaloideum or amygdala nucleus), the mammillary body (corpus mamillare), the cingulate gyrus and the parahippocampal gyrus. These anatomical units are closely connected by neural pathways. Amygdala activity is particularly important for the emotion fear and for conditional learning.
Diseases
Various cranial nerves and blood vessels pass through the openings in the cranial fossa media. Lesions in these areas can therefore lead to failure of certain nervous functions. Hemorrhages are also potentially capable of damaging tissues. In addition, they can result in supply disruptions. Lesions on cranial nerves are also possible due to injuries, inflammations and tumors. For example, nasopharyngeal carcinoma can spread via the lacerated foramen to the cavernous sinus, which drains venous blood from the brain.There, the cancer is capable of damaging cranial nerves in some cases. As part of the diagnosis of nasopharyngeal carcinoma, doctors therefore often also check the function of cranial nerves III, V, VI, IX and X. The temporal lobe of the cerebrum is located in the cranial fossa media. In temporal lobe epilepsy, affected individuals suffer from seizures, which in most cases begin between the ages of 5 and 10. Medical science distinguishes temporal lobe epilepsy between a lateral/neocortical variant on the one hand and a mesial form on the other. The temporal lobe also contains the entorhinal cortex, which is affected by neuronal atrophy in Alzheimer’s dementia. Damage to the temporal lobe or surgical removal of tissue can also lead to memory impairment in other contexts. One example is anterograde amnesia, in which affected individuals have limited ability to acquire new declarative knowledge, episodic memories, and other memory content. The clinical picture became known through Henry Gustav Molaison, who had large parts of the temporal lobe removed by a surgeon in order to treat his epilepsy. As “Patient H. M.”, his severe memory disorder caused a sensation and was extensively studied. The causes of Wernicke’s aphasia also lie in the temporal lobe. The language disorder manifests as an impairment of speech comprehension and is also known as sensory aphasia. In bilateral temporal lobe syndrome or Klüver-Bucy syndrome, patients show limited ability to perceive emotions. Increased sexual behavior (hypersexuality) is possible. In addition, other symptoms such as abnormalities in visual processing may occur.
