It is a closed sac having two layers: the visceral layer (epicardium), immediately surrounding the heart, and the outer parietal layer, forming the sac, composed of strong fibrous tissue, the fibrous pericardium, lined with a serous membrane, the serous pericardium. Synonym(s): heart sac, theca cordis.
The right and left cavernous sinuses are interconnected by the anterior and posterior intercavernous sinuses. Tributaries of the cavernous sinus include the superior ophthalmic, superficial middle cerebral, and inferior cerebral veins and the sphenoparietal sinus.
When we evaluate the sinuses for sinusitis, we look for thickening of the lining of the sinus. Note on the patient's left side (your right) at the + sign, there is a very sharp distinct border between the black air in the maxillary sinus and the white bone.nother important structure is the  ostiomeatal unit  which is the outflow tract from the sinuses and includes the ostium of each sinus as well as the meati. When blocked, the ostiomeatal unit can cause obstruction of the sinuses, analogous to putting a plug in a bathtub.