Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5776_Библиотеки_им_академика_М_И_Перельмана

is usually more diffi cult (for further reading on proximal VA stenosis, see Case 45). The detectable V1- and V2-VA segments revealed a mild poststenotic fl ow pattern, indi- rectly suggestive of a hemodynamically relevant proximal stenosis. When in doubt, extracranial continuous-wave Doppler sonography may depict the VA off shoot signal as the small Doppler probe facilitates signal detection be­hind the clavicle. However, our patient’s concomitant bi­lateral ICA and contralateral VA occlusion made it unclear whether part of the poststenotic appearance was related to hyperperfusion in the single remaining brain-supplying artery. Finally, MRA clearly disclosed a high-grade stenosis, leading to readjusted evaluation of ultrasound fi ndings.

distal collateral activation. The VA has numerous extrac­ranial anastomoses at all levels of its extracranial course which can potentially serve as collaterals and prevent occlusion over its entire length. These are anastomoses from the thyrocervical trunk and muscular rami of ECA branches, especially from the occipital artery. Spinal rami of the contralateral VA can also participate in collat­eral blood supply. During a proximal VA occlusion, these collaterals, depending on their quantity and quality, may cause a secondary VA fi lling with “postocclusional” VA fl ow of varying magnitude detectable in the distal VA segments (see Fig. A5.77, Fig. A5.78, A5.79). Complete occlusion of the entire extracranial VA is rare. In the pres­ence of two equivalent VAs, the above-mentioned collat­eral pathways are rarely of importance as the contralat­eral VA will provide the blood supply to the posterior circulation and also retrograde via a vertebro-vertebral overfl ow toward the PICA of the aff ected VA. However, if contralateral VA hypoplasia or PICA termination is pres­ent, the extracranial anastomoses become relevant. In these instances, the distal VA fl ow is usually antegrade with a typical poststenotic fl ow pattern. Although the term “poststenotic” seems slightly inaccurate in a vessel segment distal to an occlusion, we would suggest its use nevertheless, as it clearly illustrates the common prob­lem of hemodynamic impairment in stenoses and oc­clusions. A distal extracranial VA occlusion, in contrast, may cause a stump signal (as seen in our patient), a high pulsatile fl ow signal with absent end-diastolic fl ow, or a biphasic or triphasic waveform comparable to an ECA branch, as its communication to these vessels usually re­mains open (see Fig. A5.80). For example, one study that included 10 distal VA occlusions (proximal to the origin of the PICA), reported that all subjects had zero diastolic fl ow (Saito et al 2004). From both radiologic and clin­ical viewpoints, it has to be emphasized that the term “VA occlusion” alone is not suffi cient. Ideally, it should be complemented by the exact location of the occlusion and information regarding possible secondary VA fi lling by collaterals distal to the occlusion. For further reading, see also Case 19 and Case 45.

Cerebral CT (CCT) scan on the day of admission revealed ischemic infarction in the anterior and posterior territo­ries of the right middle cerebral artery (MCA). MRI was not performed (Fig. B13.1).