There are a variety of pathologic conditions that can affect CS. These conditions include neoplasms, inflammatory and infectious diseases and vascular pathologies. Tumor involvement of the cavernous sinuses may be due to direct invasion of nearby lesions, being the most common pituitary macroadenomas and meningiomas. The lesions of vascular etiology, being the most common cause aneurysms, are another entity to be considered in front of a CS syndrome of uncertain etiology.
The technique of choice for study is MRI that can identify primary tumors and can evaluate the spread of the non-neoplastic process affecting CS, although CT can help recognize and identify some anomalies, such as bone involvement.
The systematic analysis of the CS is first based on the analysis of its volume and then on the analysis of its signal, the morphology and the enhancement of the ICA, the lateral wall and the posterior edge. Moreover, the skull foramina, the neighboring regions (orbit, sella turcica, sphenoid sinus, nasopahrynx) and the brain should be studied.
We describe and illustrate the most common radiological patterns of lesions that could affect the CS.
1.Tumors
Pituitary adenoma
The pituitary adenomas represent the most frequent lesions invading the CS. This tumor is developed into the sella turcica and extends laterally to the CS, in opposition to other diseases originating from the CS. Macroadenomas (>1 cm) appear hypointense on T1-wi and hyperintense on T2- wi. They enhance less than normal pituitary tissue after contrast agent administration. Invasion may be more extended laterally after perforation of the lateral wall of the CS, displacing the ICA without narrowing (Fig.4).
Meningioma
It arises from the arachnoid cells of the dural wall surrounding the CS. On MRI, the meningioma appears isointense to gray matter on T1 wi, and with a variable signal on T2-wi. It may contain calcifications (hypointense dots on T1 and T2-wi), and it is characterized by its strong enhancement after contrast administration. It is distinguished from pituitary adenoma by the presence of a large dural base and the constriction of the intracavernous ICA lumen (Fig.5).
Schwannoma
Within the CS, intracranial schawannomas arise from cranial nerves III and V. Schwannoma is a well delimited mass appearing iso to hypointense comparing to the gray matter on T1-wi, hyperintense on T2-wi and enhances after contrast. Schwannoma may have a typical dumbbell-shape especially for trigeminal nerve within the Meckel’s cave and cavernous sinus (Fig.6).
Chondrosarcoma
CS may be invaded by a chondrosarcoma, arising from the petroclival synchondrosis. The tumor shows a characteristic high T2-wi signal and heterogeneous T1-wi signal due to hemorrhage or mucin. An important feature is the presence of calcifications that may be speckled and/or amorphous on CT.
Chordoma
It is a rare malignant tumor usually developed close to the spheno-occipital synchondrosis and may invade the CS. It appears as a soft tissue mass, hypo to isointense on T1-wi and hyperintense on T2-wi. It shows heterogeneous and important enhancement. CT images show bone destruction and intratumoral calcifications
Cavernous sinus metastasis
Metastases are rare and secondary to perineural or hematogeneous extension. By hematogenous route, metastases are seen frequently with lung and breast carcinoma followed by renal, thyroid and gastric carcinoma. CS appears enlarged by an enhanced tissular mass. By perineural spread, head and neck tumors can invade the CS. This invasion is commonly seen in adenoid cystic carcinoma and squamous cell carcinoma, lymphoma, melanoma, basal cell carcinoma, nasopharyngeal angiofibroma, and rhabdomyosarcoma. MR imaging is particularly useful in detecting perineural spread. The perineural spread is depicted by an enlarged and enhanced nerve associated with an enlargement of its foramina.
2.Vascular lesions of cavernous sinus
Intracavernous aneurysm
Intracavernous aneurysms can be secondary to trauma or septic thrombophlebitis. They appear with T2 hypointensities related to flow voids. The signal may be heterogeneous in voluminous aneurysms due to calcifications and intracellular deoxy or methemoglobin. T1 hyperintensities are caused by subacute thrombosis(Fig.7). Vascular sequences (such as 3D-TOF) are mandatory to evaluate the aneurysms.
Carotid-cavernous fistula (CCF)
CCF is an abnormal communication between the cavernous sinus and the ICA or the meningeal arterial branches of CS. It may be spontaneous or secondary to a traumatism. On enhanced CT, an enlarged cavernous sinus associated with a dilated superior ophthalmic vein and uni or bilateral exophtalmos can be seen (Fig.8). The MR findings suggesting the diagnosis are flow voids within the cavernous sinus and hyperintensity on arterial 3D TOF.
Cavernous sinus thrombosis
CS thrombosis may be idiopathic or secondary to spread of infection from the sino-nasal cavities and the orbits. Highsignal intensity on T1 and T2-wi appears in sub-acute thrombus. Diagnosis in acute stage may be difficult as thrombosis appears isointense on T1 and T2-wi. Contrast-enhanced images help the diagnosis by showing a filling defect with surrounding rim enhancement. Other imaging findings include enlargement of the CS, dilated superior ophthalmic vein, proptosis and increased enhancement of the ipsilateral tentorium.
3.Infections of CS
CS infectious involvement is usually secondary to direct extension from adjacent sino-nasal infections, including commonly Staphylococcus aureus. Patients present with cavernous sinus thrombophlebitis and local signs of the primary infection. MR findings include enlargement of CS and the change of its signal intensity, features of CS thrombosis and adjacent inflammation. Diffusion-weighted MRI helps to detect small lesions. It may show restriction of diffusion at the site of infection. Reversible ICA stenosis may occur, and it disappears after treatment.