There can be no question that middle-ear disease is responsible for the very great majority of cases of lateral sinus thrombosis, and whether the infection takes place by extension of thrombus along the connecting veins (thrombo-phlebitis), or after destruction of the osseous barrier (osteo-thrombosis), the results are more or less identical.
Thrombosis first occurs in that part of the sinus which is in closest relation to the primary cause of the infection, the clot rapidly increasing in size until the lumen of the sinus is entirely obliterated. In its early stages the thrombus is of a chocolate colour, softening at a later date and breaking down into a purulent material. Many varieties of bacteria may be present though the infection is mainly dependent on the presence of the streptococcus pyogenes.
Two changes may now occur:—(1) the central portion of the thrombus, having softened into a purulent material, may be limited by the firmer thrombus in front and behind; and (2) the thrombus may extend into the neighbouring and connecting venous channels downwards along the course of the internal jugular vein, backwards along the course of the lateral sinus, inwards along the course of the superior petrosal sinus, outwards along the line of the mastoid emissary vein, downwards through the posterior condyloid foramen, and inwards along meningeal veins.
The symptomatology may be considered as follows:—
(1) Symptoms dependent on the extension of the thrombus to neighbouring venous and lymphatic channels.
(2) Symptoms resulting from toxic absorption or dependent on the transmission of infected material to other parts of the body.
1. Symptoms dependent on the extension of the thrombus to neighbouring venous and lymphatic channels. When the thrombus spreads downwards along the course of the internal jugular vein, there is swelling and tenderness along the line of the vein. The vessel, though thrombosed in its upper part—perhaps throughout its whole extent—is itself seldom palpable, the cervical swelling usually being dependent on associated lymphadenitis and lymphangitis. In those few cases where the thrombosed vein can be felt, resembling a ‘buried lead pencil’, the thrombus is sometimes of the non-infective type.
The combined venous and lymphatic involvement causes œdema of the tissues, pain, and rigidity on attempted movement. The anterior and external jugular veins may become engorged from the extra strain thrown upon them. Subsequently, the inflamed parts may break down and extensive cervical suppuration result.
When the thrombus spreads backwards along the course of the lateral sinus, the coagulation process may extend as far as the torcula and even further. Evidence as to the nature and extent of the process is not always apparent, though one expects to find some œdema of the overlying scalp tissues.
When the process spreads inwards along the course of the superior petrosal sinus there is considerable risk of involvement of the corresponding cavernous sinus, possibly of the opposite sinus also (see [p. 288]).