Indications. (i) In doubtful cases to decide whether thrombosis exists or not.
(ii) As a preliminary to opening the sinus with or without ligature of the jugular vein.
Operation. The first step is to perform the complete mastoid operation, except in the case of acute inflammation of the mastoid process, when Schwartze’s operation will be sufficient.
To expose the field of operation more freely, an incision an inch or more in length is made horizontally backwards, beginning at the mid-point of the posterior margin of the primary incision ([Fig. 216]), the soft parts being reflected upwards and downwards from the bone, and the flaps so formed being then retracted. Above, the bone should be exposed beyond the level of Reid’s base-line, which roughly corresponds to the line of the transverse sinus; below, the tip of the mastoid should be cleared until the mastoid vein is reached. If it be thrombosed it may be assumed that the lower part of the lateral sinus is also thrombosed. Bleeding from the bone at this point may be arrested by temporarily plugging the foramen with a fragment of sterilized wax.
The condition found on opening the mastoid process varies considerably. If the result of acute inflammation of the mastoid process, the mastoid cells surrounding the sigmoid sinus usually contain pus or granulations, on removal of which a fistula may be seen to communicate with the outer wall of the sinus; or the bone around the sigmoid groove may already be destroyed, with free exposure of the sinus within the wound. With this there is frequently an extra-dural abscess. In other cases, if the infective process has been very virulent, evil-smelling pus, sometimes intermixed with bubbles of gas, may escape on chiselling through the mastoid cortex. This is a sure sign of extensive disease, the sinus wall often being gangrenous and the bone surrounding it necrosed and discoloured.
If occurring in the course of a chronic middle-ear suppuration, very little disease of the mastoid process may be found except along the path by which the infection has spread.
After the sinus wall has been reached, sufficient bone should be removed to expose its outer surface for at least half an inch above and below the supposed infected area.
The decision as to whether thrombosis exists or not may have to be made during the operation itself, and is based partly on the appearance of the sinus wall and partly on the symptoms, the relative value of each varying in each individual case.
Normally the sinus pulsates and is of a bluish-grey colour. If thrombosed, the wall of the sinus may be of a yellow or dark colour and may not pulsate, but neither discoloration nor the absence of pulsation is an absolutely reliable sign of thrombosis. Again, if the sinus be covered with granulations or purulent lymph, it is sometimes impossible to say whether it is thrombosed or not, especially if the clot is limited and parietal. Further, the thrombus may be situated low down towards the jugular bulb, so that if it has not extended very far upwards the exposed portion of the lateral sinus may still be normal in appearance. Palpation of the sinus with the finger or aspiration with a hollow needle is sometimes advised as an aid to diagnosis. These procedures, however, are extremely unwise, owing to the risk of dislodging a small fragment of the infected clot, which may easily occur if the latter does not obliterate the sinus completely. As a means of diagnosis the withdrawal of blood by the aspirating needle is of no value, as it does not negative the presence of a parietal thrombus, owing to the possibility of the needle passing through it into the free lumen of the sinus.