Kenneth

C. Wright,

PhD

Percutaneous

I

a continuing

N

matters,”

Transcatheter

effort

cessfully

to improve

Dr Charles

T. Dotter

in the

vasculatune

(1). His

sure

should

that “what operative (1). This was the stent placement

be”

evaluated

work

based on the premise accomplished without

was

can be expobirth as we

of transcatheter know it today. Despite Dotter’s early studies, his technique was not used clinically because of significant luminal narrowing that

occurred

Fourteen

within

years

the

passed

stents

cation of another article intraluminal scaffolding

veins,

bile

main-stem

results

with better

and

have

of the

bron-

been

ing suit

longitudinal in easier

and

and

flexibility should more successful

possibly

better

en-

experi-

stents during general pninci-

their use have emerged. risks associated with

of an endoprosthesis must against those associated available corrective mea-

sures. This usually means, do the risks associated with the stenting procedure and permanent stent placement out-

stent. First, it is imperative to accurately locate the lesion fluoroscopically to ensure proper positioning of the endoprosthesis. Bony landmarks, external markers, and radiographs obtained during intraluminal contrast material injection have all been used singly or in combination for this purpose. Second, the stent must be placed so that it bridges the affected segment completely. In short strictures, the stent should

be centered support longer

and to prevent lesions, the stent

Developed as an adjunct to balloon dilation, stents are mechanical devices placed within the lumen of tubular structures to maintain patency by pro-

before,

should

extend

viding mural support. Although prostheses differ in construction,

the

been

additional

configurations

have

described.

basic mechamemory, deformation.

Since Dotter’s have effectively

report, stenoses

by disease, fibrosis, or torsion vided mural support in cases or dysplasia. They have been

during,

and proof malacia used suc-

has

stent

lesion

have ence

stents caused

and

placement

Before

these they

all possess one of three nisms of action: thermal spring action, or plastic

original dilated

stent ed.

tumors between stenosis

terms:

Blood

9.722,

vae,

grafts

vae,

interventional

nae

and

cavae,

vessels,

9*782

stenosis

prostheses,

#{149}

982.1299

procedure,

stenosis

on ob-

Venae

#{149} Editorials

#{149} Venae

982.1299

on obstruction,

caCa-

#{149} Ve-

982.72,

982.78

Radiology

1990;

176:620-621

‘From the Department of Diagnostic Radiology, University of Texas M.D. Anderson Cancer Center, Box 057, 1515 Holcombe Blvd. Houston, TX 77030. Received and accepted May 18, 1990. Address reprint requests to the author. 2

9*

indicates

generalized

volvement. RSNA, 1990 See also the article by Furui 670)

620

in

this

issue.

vein

and

et a! (pp

artery

665-

in-

time

after

recommend-

the cause

be determined.

not functioned of intraluminal

of

well in the presneoplasia. Since

overcome

this limitation,

nal

Most

stents

for maximum migration. or stents

the entire

the normal

surface.

dependent

length

In

of the

Accurate

and

stented

stent

on operator

lumi-

placement

experience

is

and

sufficient stent opacity for easy fluoroscopic visualization in the area of deployment. Finally, the stent should not

covered

stents are currently being developed and evaluated (3,4). In addition, the sion must be negotiable and amenable

on the lesion

stricture so that some overlap onto healthy tissue occurs at each end. In this way, there is a smooth transition

between

Stents

can grow through the spaces the struts of the stent, luminal and occlusion will recur. To

to dilation.

Index

been

placement,

must

such that they are possible to retrieve struction,

for some

long-

Three general principles are involved in the actual placement of a

sible complication is infection of the stented area. Because of this, administration of a broad-spectrum antibiotic

quently,

re-

term results. Also, the size of the introducing system and the stent wire may restrict the use of a specific endoprosthesis in lumens of small diameter.

weigh the risks associated with general anesthesia and major surgery? One pos-

known as stents. Then, between 1983 and 1987, nine different stent designs were discussed in the literature. Subse-

Placement’

placement

esophagus,

not

extensive

ence with transcatheter the past 7 years, certain

placement be weighed with other

the publi-

dealing devices,

and

in the ureter

but, to date, couraging. As a result

ples governing Initially, the

(2).

before

and

the trachea

chi, and the male urethra. Endoprostheses have also been experimentally

ceived, developed, and evaluated a method for percutaneous introduction and placement of tubular endoprostheses

in arteries

ducts,

con-

Stent

le-

are designed

difficult if not imonce they are released. Therefore, if they fail to adequately dilate the stenosis and cannot be removed, significant complications may occur. Although a second stent can be placed within the first to increase the expansion force, the strength of the stricture can easily be evaluated by balloon dilation before initial stent placement. However, in at least one case, stent placement has successfully reconstituted the lumen of a structure after balloon dilation failed to expand the stenosis (5). When selecting a stent design, one must take into account the approach to and location of the lesion. If the approach is tortuous or if the narrowing lies within a curved segment of the structure, selection of a stent possess-

“overdilate” ed diameter

the structure. The expandof the prosthesis should

not be more times greater

than approximately than the diameter

normal

lumen.

Overdilation

can result

in mural necrosis, perforation, inflammation, and subsequent ing due to cellular proliferation.

Once

in place,

stents

1.2 of the

should

fibrosis, thicken-

be radio-

graphed in at least the anteropostenior and lateral projections. Since it is possible for a prosthesis to open elliptically, adequate evaluation of expansion can be accomplished only by viewing the implant in two planes. In addition to the aforementioned general principles involved in the use of transcatheter stents, certain fundamentals exist governing their use in

the vasculature. Intravascular stent placement has been developed for improved patency of both arteries and veins. In atheromatous lesions, stents have been used after angioplasty to prevent elastic recoil of the artery and to correct longitudinal

dissection of the intima. These devices have been suggested for the correction of dissecting aneurysms, and covered

is still

stents

branches. Three additional patients with BuddChiari syndrome resulting from recurrent idiopathic obstruction or severe stenosis of the hepatic IVC were successfully treated with stent placement.

are

treatment eurysms in the

being

evaluated

for saccular (6). Stents management

fusiform

have also been of hemodialysis

anused

and portosystemic shunts. In addition, endovascular prostheses have proved useful in maintaining the luminal diameter of vessels narrowed by fibrosis, including

scarring

from

This

inflammation,

projections

been

Volume

reported

176

showed that by the stents similar results for

other

#{149} Number

stent

and

3

first

ostia

such

of large

reported

re-

of placing collateral

use

of

stented.

The

prostheses

over

a 7-10-

period, although intiwas observed within

Neointimal covering of the is important, since it reduces of thrombosis, infection,

migration.

However,

in some

to come into direct contact with the adjacent cells. In addition, stent design may affect the intimal response. Placement of balloon-expanded stents has been shown to produce histopathologic changes in the vascular wall that resemble those associated with angio-

plasty,

whereas

placement

of thermal

memory and spring action stents has not. Although excessive neointimal hyperplasia can be removed (8), studies are being conducted to determine

whether the process can be controlled. To date, both steroid and anticoagulant therapies have been unsuccessful. Another concern unique to vascular stent placement is excessive clot forma-

the hepatwere pahave it

gulability, it should be corrected stent placement. Finally, if poor

to or outflow ists,

tion on the stent wire. This can result in stenosis, occlusion, and embolization. If clot is present, it should be lysed, if possible, before stent placement. If the patient exhibits hypercoa-

the

from

chance

before inflow

the stented

of stent

area

ex-

thrombosis

is

increased. In conclusion, percutaneous transcatheter stent placement will never replace the use of balloon dilation catheters, lasers, atherectomy devices, or tissue welding systems. Instead, it will be used in conjunction with these modalities to help overcome certain limitations. The clinical applicability of stents will continue to expand as new

and

innovative

tions

are

designs

developed

and

and

modifica-

refined.

U

References 1.

in-

stances, excessive neointimal proiiferation within a stent has resulted in significant luminal narrowing. The actions of plateletand endothelialderived growth factors on the cells of the intima have been implicated in this process. Angioplasty may play a role, since balloon dilation often produces intimal tears that allow these mediators

evaluate

designs,

conclusions

risks

recurrence

the stents. stent wire the chance

the degree of stent expansion. Autopsies performed at 3 and 7 weeks after

stent placement ic veins bridged tent. Although

the

month follow-up mal thickening

in at least

to adequately

is the

prevented

pansion of the prostheses could have been attempted or additional stents could have been positioned within the previously placed implants to increase the expansion force. In four of the six patients, the IVC was dilated ellipitically, which emphasizes the need for two

across

subsequently

sue of Radiology, Furui et al (7) describe the use of Gianturco expandable metallic stents in the hepatic segment of the inferior vena cava (IVC) for correction of extrinsic tumor compression as well as idiopathic obstruction accompanied by Budd-Chiani syndrome. In six patients with hepatic tumor compression of the IVC, stents were placed without prior balloon dilation. In every case, the prostheses dilated the IVC and the debilitating edema of the lower body disappeared. Had the stents failed to dilate the compressed segment, two options were available. Since this stent is not retrievable, balloon ex-

radiographs

to draw

transcatheter stents. In each case, the lesion was first balloon dilated and

radiation therapy, and surgery for tumon resection, organ transplantation, and vascular graft implantation. Vascular stents have also been used successfully to open vessels compressed by extrinsic tumors. In this is-

postplacement

early

the long-term

stents

as a possible

and

too

garding

Dotter

CT.

spring

endartenial

patency 2.

3.

tube

in canine

Radio!

1969;

Dotter

CT,

coil-

grafts:

popliteal

long-term artery.

Invest

4:329-332. Buschmann

RW,

McKinney

MK,

Rosch J. Translumina! expandable nitinol coil stent grafting: preliminary report. Radiology 1983; 147:259-260. Alvarado R, Pa!maz JC, Garcia OJ, ho FO, Rees CR. Evaluation of polymer-coated balloon-expandable stents in bile ducts. Radiology

4.

Tnanslumina!ly-p!aced

1989;

170:975-978.

George PJM, Irving JD, Mantel! BS, Rudd RM. Covered expandable metal stent for recurrent tracheal obstruction. Lancet 1990; 335:582-584.

5.

6.

7.

8.

Irving JD, Adam A, Dick R, Dondelingen RF, Lundenquist A, Roche A. Giantunco expandable metallic biliary stents: results of a European clinical trial. Radiology 1989; 172:321-326. Minich D, Wright KC, Wallace 5, et al. Percutaneously placed endovasculan grafts for aortic aneurysms: feasibility study. Radio!ogy 1989; 170:1033-1037. Furui 5, Sawada 5, Inie T, et a!. Hepatic inferior vena cava obstruction: treatment of two types with Gianturco expandable metallic stents. Radiology 1990; 176:665-670. Vonwenk

D, Guenther

tima! hyperplasia ses

AJR

by

RW.

athenectomy

1990;

Removal

of

in-

in vascular endopnostheand

balloon

dilatation.

154:617-619.

Radiology

#{149} 621