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PERIPHERAL VASCULAR ULTRASOUND
Figure 14.19 A transverse color flow image of a vein graft demonstrating an arteriovenous fistula (arrow). The Doppler waveform displays low-resistance, high-volume flow across the fistula.
mark the level of the defect using duplex so that the surgeon can easily locate the fistula.
SEROMAS, FLUID COLLECTIONS AND
GRAFT INFECTIONS
Seromas are fluid-filled collections that are occa- sionally seen adjacent to vein grafts, particularly at the level of the groin. They can be mistaken for false aneurysms on B-mode imaging, but color flow imaging will demonstrate an absence of flow (Fig. 14.20). Fluid collections around synthetic grafts can be due to local reaction of the sur- rounding tissues, but they can also be due to graft infection. Graft infections are a serious complica- tion and are more frequently associated with syn- thetic grafts. The outcome for patients with synthetic graft infections is often poor (Mertens et al 1995). Infections at the level of the groin are common due to the rich source of bacteria in this region, and aortobifemoral, iliofemoral and axillobifemoral grafts are especially at risk. Complications of infec- tion can lead to the disintegration of a graft anas- tomosis, resulting in severe hemorrhage. Failure of wound healing is also a frequent complication. Ultrasound imaging can be useful for investigating wound infections, as the B-mode image can show whether the graft is in direct contact with sus- pected areas of infection, especially if the suspected region tracks to discharging wounds or openings
Figure 14.20
vein graft (VG).
A fluid-filled seroma (S) adjacent to a
S
VG
on the skin surface (Fig. 14.21). It is essential to image any suspected area of graft infection in cross- section to see how it relates to the graft and surrounding structures. It can be difficult to differ- entiate areas of infection from simple hematomas, and bacterial cultures are often required to isolate infective organisms. Ultrasound can be used to guide the needle puncture during the sampling of fluid collections to avoid accidentally puncturing the graft. CT and MRI are also commonly used for investigating graft infections, especially in the abdomen. Methicillin-resistant Staphylococcus aureus (MRSA) is now endemic in most hospitals. Graft infections caused by MRSA are difficult to treat, requiring prolonged use of powerful antibiotics. In some cases, graft removal is necessary to remove the focus of infection, but this may lead to inevitable amputation of the limb, owing to poor blood flow. In extreme situations, the patient may be over- whelmed by the infection and die.
REPORTING
The easiest method of reporting the scan results is by the use of diagrams. The graft position can be drawn onto the diagram with velocity measure- ments and other relevant information recorded (Fig. 14.22). It is also useful to keep a file for each patient in the graft surveillance program in the