Cribriform plate

In mammalian anatomy, the cribriform plate, horizontal lamina or lamina cribrosa (from Latin "cribrum", "sieve" + -form) of the ethmoid bone is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities.
The cribriform plate is narrow with deep grooves supporting the olfactory bulb, and is perforated by olfactory foramina allowing the passage of the olfactory nerves. The foramina in the middle of the groove are small and allows the passing of the nerves to the roof of the nasal cavity. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha.
A fractured cribriform plate can result in olfactory dysfunction, septal hematoma, cerebrospinal fluid rhinorrhoea (CSF rhinorrhoea), and possibly infection which can lead to meningitis. CSF rhinorrhoea (clear fluid leaking from the nose) is very serious and considered a medical emergency. Aging can cause the openings in the cribriform plate to close, pinching olfactory nerve fibers. A reduction in olfactory receptors, loss of blood flow, and thick nasal mucus can also cause an impaired sense of smell.
Structure.
Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a rooster's comb.
The long thin posterior border of the crista galli serves for the attachment of the falx cerebri.
Its anterior border, short and thick, articulates with the frontal bone, and presents two small projecting "alae" (wings), which are received into corresponding depressions in the frontal bone and complete the foramen cecum.
Its sides are smooth, and sometimes bulging from presence of a small air sinus in the interior.
On either side of the crista galli, the cribriform plate is narrow and deeply grooved; it supports the olfactory bulb and is perforated by foramina for the passage of the olfactory nerves. The foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity; those at the medial and lateral parts of the groove are larger—the former transmit the nerves to the upper part of the nasal septum, the latter those to the superior nasal concha.
At the front part of the cribriform plate, on either side of the crista galli, is a small fissure that is occupied by a process of dura mater.
Lateral to this fissure is a notch or foramen which transmits the nasociliary nerve; from this notch a groove extends backward to the anterior ethmoidal foramen.
Clinical significance.
A fractured cribriform plate (anterior skull trauma) can result in leaking of cerebrospinal fluid into the nose and loss of sense of smell. The tiny apertures of the plate transmitting the olfactory nerve become the route of ascent for a pathogen, "Naegleria fowleri". This amoeba tends to destroy the olfactory bulb and the adjacent inferior surface of the frontal lobe of the brain. This surface initially becomes the site of proliferation of the trophozoites of "Naegleria fowleri" and their subsequent spread to the rest of the brain and CSF. Because of its initial involvement and trophozoite presence in early phases of "Naegleria fowleri" infection, flushing of this region with saline using a device, to obtain "Naegleria fowleri" for diagnostic PCR and microscopic viewing, has been proposed for patients affected by naegleriasis, by (Baig AM., "et al") in a recent publication. Researchers have suggested the same route to administer drugs at an early phase of infection by using a "Transcribrial Device" that has been proposed to kill this pathogen at the place of its maximum proliferation. In 2017 the inventor of this device suggested that after slight modifications this method could be effective in delivery of stem cells to the brain as well. A recent Australian study has shown that the bacterium causing the tropical disease melioidosis, "Burkholderia pseudomallei," can also invade the brain via the olfactory nerve within 24 h by traversing the cribriform plate.
Keros classification.
The Keros classification is a method of classifying the depth of the olfactory fossa.
The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate. Keros in 1962, classified the depth into three categories.