Lesions and Pseudolesions of the Cavernous Sinus and Petrous Apex

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Endoscopic surgery using an expanded endonasal approach now allows surgical access to an increasing range of parasellar, suprasellar, clivus, and petrous apex lesions. Accurate preoperative planning requires proper interpretation of CT and MRI results. It is essential to identify important anatomic landmarks and to recognize the appearance of common lesions and pseudolesions. Postoperative imaging must evaluate for residual tumors and identify iatrogenic conditions.

Section snippets

Parasellar structures

The cavernous sinus consists of bilateral structures containing multiple small venous sinusoids [5]. Its floor rests on the intracranial surface of the sphenoid and temporal bones. A groove on the surface of the sphenoid bone is termed the carotid sulcus and marks the course of the horizontal segment of the intracavernous carotid. The medial wall of the cavernous sinus has a sellar portion (facing the pituitary and sella) and a sphenoidal portion (facing the body of the sphenoid). The lateral

Petrous apex anatomy

The petrous portion is the most medial aspect of the temporal bone. It is bounded medially by the petro-occipital synchondrosis (see Fig. 2), which contains embryonic rests capable of becoming chondroid neoplasms. In sagittal plane, the petrous bone has a triangular shape with anterior wall forming the posterior margin of the middle cranial fossa and the posterior wall forming the anterior margin of the posterior cranial fossa. The tentorium attaches to the apex of the triangle, with the

Imaging techniques

CT examination is best performed on a multislice scanner with axial images reconstructed at 1.25-mm or smaller intervals. Although direct coronal images were once performed, coronally oriented reformats are now technically excellent and minimize radiation dose to the patient. Both soft tissue and bone reconstructions should be performed; the latter can evaluate for subtle osseous erosion or remodeling.

Although MRI lacks the bony definition of CT, it is invaluable for demonstrating subtle soft

Parasellar lesions

Aneurysms of the cavernous carotid represent a small fraction of all cerebral aneurysms, but figure in the differential diagnosis of cranial nerve palsies. Although catheter angiography remains the gold standard for aneurysm imaging, this diagnosis should always be borne in mind when viewing CT and MRI scans of the skull base. On the most commonly used MRI sequences (spin echo), moving fluid appears as signal dropout (flow void). Unfortunately, any air-containing structure also shows signal

Petrous apex lesions

The petrous apex is pneumatized in approximately 33% of individuals. Pneumatization is asymmetric in many instances; this should be considered a normal variant and not a lesion. With the growing use of MRI as initial brain screening examination, marrow signal in the nonpneumatized apex can be misinterpreted as a mass (Fig. 12). Confirmation with noncontrasted CT examination demonstrates a nonexpansile area of fat attenuation similar to normal marrow elsewhere. Like the mastoid air cells and

Postprocedural findings

Cephaloceles result from defects in the floor of the cranium, either congenital or acquired. Iatrogenic defects are possible after surgery to either the central skull base or petrous region. Suspicion for iatrogenic dural defect should arise when pneumocephalus persists for more than a few days postoperatively. Congenital cephaloceles are much less common in the petrous apex region than in the frontonasal and ethmoidal regions, but do occur. Thin-section CT is most sensitive for bone defects,

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