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A sinus is a sac or cavity in any organ or tissue, or an abnormal cavity or passage. In common usage, "sinus" usually refers to the paranasal sinuses, which are air cavities in the cranial bones, especially those near the nose and connecting to it. Most individuals have four paired cavities located in the cranial bone or skull.
The dural venous sinuses (also called dural sinuses, cerebral sinuses, or cranial sinuses) are venous sinuses (channels) found between the periosteal and meningeal layers of dura mater in the brain. [ 1 ] [ 2 ] They receive blood from the cerebral veins , and cerebrospinal fluid (CSF) from the subarachnoid space via arachnoid granulations .
The skull is composed of three types of bone: cranial bones, facial bones and ossicles, which is made up of a number of fused flat and irregular bones. The cranial bones are joined at firm fibrous junctions called sutures and contains many foramina, fossae, processes, and sinuses.
The maxillary sinuses, the largest of the paranasal sinuses, are under the eyes, in the maxillary bones (open in the back of the semilunar hiatus of the nose). They are innervated by the maxillary nerve (CN V2). [2] The frontal sinuses, superior to the eyes, in the frontal bone, which forms the hard part of the forehead.
The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain.The skull is also known as the cranium. [1] The cranial cavity is formed by eight cranial bones known as the neurocranium that in humans includes the skull cap and forms the protective case around the brain.
The sphenoid bone [note 1] is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of the occipital bone. The sphenoid bone is one of the seven bones that articulate to form the orbit. Its shape somewhat resembles that of a butterfly, bat or wasp with its wings extended.
Frontal sinus. Each frontal sinus is situated between the external and internal plates of the frontal bone. [1] [2] Their average measurements are as follows: height 28 mm, breadth 24 mm, depth 20 mm, creating a space of 6-7 ml. [3]
The cavernous sinus receives blood from: [2] Superior and inferior ophthalmic veins [3]; Sphenoparietal sinus [3]; Superficial middle cerebral veins [3]; Inferior cerebral veins; Blood leaves the sinus via superior and inferior petrosal sinuses as well as via the emissary veins through the foramina of the skull (mostly through foramen ovale).