174 CLINICAL APPLIED ANATOMY. 



Traumatic thrombosis is usually associated with fracture, and is 

 frequently inflammatory when it ranks with the next group. 

 Inflammatory thrombosis may be due to direct extension of 

 contiguous inflammation to the sinus walls, or the infection may 

 be carried to the sinus by veins which drain an inflammatory 

 focus. 



The lateral sinus is involved more frequently than any of the 

 others. Its intimate connection with the ear accounts for this, 

 an inflammatory process being set up by extension of caries 

 from the antrum or tympanum to the bony groove in which the 

 sinus lies. The sinus may also be infected by certain of the 

 tributary veins which it receives from the ear. The petro- 

 squamous vein, which receives radicles from the tympanum and 

 attic, joins the lateral sinus behind, and also communicates with 

 the middle meningeal vein in front. The blood from the laby- 

 rinth, and from the cochlea, is returned by the internal auditory 

 veins, which open into the inferior petrosal sinus, which is in 

 turn a tributary of the lateral sinus. 



Thrombosis of the lateral sinus may spread to the sinuses 

 which communicate with it, or to the opposite lateral sinus across 

 the torcular by venous communication. The right lateral sinus 

 usually communicates chiefly with the superior longitudinal 

 sinus, which drains the cortical regions of the brain, whilst the 

 left is continuous with the straight sinus which receives blood 

 from the ventricles and basal ganglia. Sometimes the throm- 

 bosis extends along the petrosal sinuses to the cavernous sinus 

 or to the veins of the hemisphere. 



The efferent veins of the lateral sinus are the internal jugular, 

 the mastoid, and the posterior condylar. Extension of the infec- 

 tion to the jugular vein gives rise to a tender cord-like swelling 

 under the sterno-mastoid ; the surrounding lymphatic glands are 

 also enlarged, and rarely the inflammation attacks the nerves 

 which pass out through the jugular foramen. The jugular blood 

 stream may also convey infection to the lungs, giving rise to infarc- 

 tions and abscesses. Theoretically it is possible for the jugular 

 bulb to be directly infected from the inner ear by means of the 



