Surgical Anatomy

The skull base is made up anteriorly of the posterior wall of the frontal sinus, which is thick frontal bone that extends posteriorly to form the roof of the ethmoid sinuses (fovea ethmoidalis) on either side of the cribriform plate that comprises part of the ethmoid bone (Fig. 15.2). The cribriform plate joins the fovea through the lateral lamella and this can be almost non-

Middle Turbinate Fovea Ethmoidalis
Fig. 15.2 A disarticulated ethmoid bone showing the cribriform plate with the crista galli above and the vertical plate of the ethmoid below.

Fig. 15.3 Arrow a indicates the roof of the ethmoid sinuses; arrow b indicates the lateral lamella, and arrow c indicates the medial aspect of the cribriform plate.

Cribriform Defect Csf Rhinorrhea

Fig. 15.5 Idiopathic CSF leak through the posterior wall of the sphenoid sinus near the midline.

Fig. 15.4 CSF leak due to a small encephalocele of the right cribriform plate.

Fig. 15.5 Idiopathic CSF leak through the posterior wall of the sphenoid sinus near the midline.

existent when the cribriform plate and fovea eth-moidalis are on the same plane, or it can form the thin vertical bone connecting them, depending on how far the cribriform plate dips into the nose (Fig. 15.3). Posteriorly, the sphenoid sinus and posterior ethmoidal air cells form the inferior relationship of the skull base.

The commonest site of a spontaneous CSF leak is the area of the cribriform plate where dura around the olfactory nerves appears to have extended through the cribriform plate and ruptured (Fig. 15.4). The next most common leak is from a very well-pneumatized sphenoid sinus (Fig. 15.5). A high-pressure system may be a contributing factor in these cases and a shunt or ventriculostomy may be required.

CSF leaks complicating intranasal surgery are often found around the lamina lateralis (the vertical

Lateral Lamella

Fig. 15.6 Postsurgical CSF leak of the lateral lamella (arrow). Fig. 15.7 CSF leak from a fracture of the lateral wall of the sphenoid sinus.

Fig. 15.6 Postsurgical CSF leak of the lateral lamella (arrow). Fig. 15.7 CSF leak from a fracture of the lateral wall of the sphenoid sinus.

Sphenoid Sagittal
Fig. 15.8 Sagittal CT scan showing a pneumocephalus (arrow) due to a CSF leak from the posterior wall of the sphenoid sinus after pituitary surgery.

thin bone joining the cribriform plate to the fovea ethmoidalis) near the anterior ethmoid artery (Fig. 15.6).

Posttraumatic CSF leaks commonly originate from the cribriform plate, the fovea ethmoidalis, and the posterior wall of the frontal sinus or sphenoid sinus (Fig. 15.7). Leaks of the anterior and middle cranial fossa occurring after neurosurgical procedures most commonly follow pituitary surgery (Fig. 15.8). Post-

neurosurgical leaks also come from the posterior wall of the frontal sinus when it has not been cranialized, and they are more likely if a pericranial flap has not been used to repair any dural defect.

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