PRACTICAL CONSIDERATIONS : THE MIDDLE EAR. 1509 



squamous suture (causing a fluctuating adenomatous postauricular swelling, pushing 

 the pinna forward and making it unduly prominent). (5) Inward, either through 

 venules passing to the sigmoid sinus, or through caries of the wall of the sigmoid 

 groove (causing external pachymeningitis, or subdural abscess, or suppurative basal 

 meningitis, or cerebellar abscess — by way of the cerebellar veins emptying into the 

 lateral sinus — or, most frequently, sigmoid sinus thrombosis). 



The sigmoid sinus is usually about i cm. behind the suprameatal spine, but is 

 occasionally so far forward as to lie just beneath the external surface of the mastoid 

 process, and immediately behind the bony wall of the meatus. 



Owing to its close relation to the mastoid antrum and cells, no other cranial 

 sinus is so frequently the seat of infective inflammation. In infants, however, it is 

 seldom seen, owing to the following facts : First, the mastoid cells are not developed 

 in them, though the antrum exists ; secondly, the squamous covering of the antrum 

 is not yet soldered to the mastoid, and therefore, purulent matter finds a ready exit, 

 not being enclosed in a complete bony casing ; thirdly, more numerous exits for 

 the venous blood exist in infants than in adults ; and fourthly, the sigmoid sinus 

 rests on a flatter osseous surface than in adults, the bony gutter which imbeds the 

 adult sinus being not yet fully formed. In infants the internal ear is more exposed 

 than in adults to pathological encroachments from the middle ear, hence in them 

 leptomeningitis is apt to ensue, which frequently ends fatally, and that so rapidly as 

 to prevent the formation of sigmoid sinus thrombosis (Macewen). 



When the sigmoid sinus is infected, extension may occur to the venous channels 

 associated with it, especially to the internal jugular, anterior condylar, and deep veins 

 of the neck into which the anterior condylar empty themselves. Evidence of involve- 

 ment of these may be found in two areas, — along the internal jugular, and in the upper 

 third of the posterior cervical triangle. Pain on pressure over the inflamed veins may 

 be elicited even when the patient is deeply somnolent or semi-conscious. Thrombosis 

 of the internal jugular when marked, is very easy of detection, as it lies so super- 

 ficially. The finger perceives a cord-like formation to the inner side of the sterno- 

 mastoid on the outer side of the artery, though the latter is sometimes overlapped by 

 it. This may extend the whole length of the internal jugular, but it is frequently 

 confined to the upper third. The entire thrombus may be disintegrated and its par- 

 ticles carried by the current to the lung, where they may set up infective infarction. 

 They may be carried to the lungs by the veins passing into the posterior cervical 

 triangle which flow through the vertebral and other channels to the subclavian 

 (Macewen). 



The complication most to be feared in middle ear disease is the spread of the 

 infection to the interior of the cranium. This may occur by direct extension of 

 the carious process through the bone ; more rarely through the labyrinth and internal 

 auditory canal or the aqueducts ; or, still more rarely along the small blood-vessels 

 or connective tissue fibres which pass through the bone between the middle ear and 

 the dura. Very exceptionally the pus may find its way through the thin anterior 

 wall into the carotid canal and along this to the cranial cavity. 



Although otitis media appears to occur on both sides with equal frequency, the 

 right side of the head has been said to be more frequently affected by intracranial 

 sequelae. If so, this is probably due to the greater size of the lateral sinus and the 

 sigmoid sinus on the right side. Consequently the right sigmoid sinus encroaches 

 more upon the petrous and the mastoid portions of the temporal bone, especially at 

 the sigmoid knee, and the distance between the lower border of the tympanum and 

 the antrum on the one hand and the sigmoid sinus on the other, is less than between 

 the corresponding points on the left side (Macewen). 



Involvement of the internal ear from otitis media is comparatively rare. This 

 portion of the ear is developed independently of the rest, and, after necrosis, may be 

 extruded in sequestrae, in which may be recognized the structure of the labyrinth. 

 If the pus associated fails to escape externally, there is danger of its passing through 

 the internal auditory meatus and aquaeductus vestibuli to the brain. Affections of the 

 semi-circular canals produce disturbances of equilibrium. 



The sinus is in danger in operations on the antrum, the external opening for 

 which should be immediately behind the meatus, and the centre of the opening 2-3 



