Fig. 24.4  (Left) The whole extent of the 6-cm long cyst surrounding the popliteal artery

24.1  Commentary

Trauma has been ruled out overwhelmingly on the grounds that the disease would be seen predominantly in people engaged in competitive sports: this is not the case. All cases of adventitialcysticdiseasereportedintheliteraturehaveoccurredinnonaxialvesselsduring limb differentiation and development. It is therefore postulated that during limb bud development, cell rests derived from condensations of mesenchymal tissue destined to form the knee, hip, wrist or ankle joints are incorporated into the nearby and adjacent nonaxial vessels from vascular plexuses during the same stage of development, and in close proximity to the adjacent condensing joint structures.3 It is postulated further that these cell rests are then responsible for the formation of adventitial cystic disease in adult life, when mucoid material secreted results in a mass lesion within the arterial or venous wall.3 Figure 24.7 shows a row of cross-sections of a resected and totally occluded popliteal segment. In this

Fig. 24.5  (Right) The perivascular cyst being resected, with the artery remaining intact

case, the cyst is clearly in the midst of the arterial wall and does not appear to be located in the adventitia.

According to the hypothesis of Levien and Benn,3 popliteal adventitial cystic disease manifests itself in adults. Early cases manifest in the third decade, but most cases occur in the fourth and fifth decades; it occurs less frequently in later stages of life.4 The male: female ratio is about 5:1. In summary, there is little doubt that popliteal cystic disease is congenital. [Q1]

Popliteal adventitial cysts are located mostly in outer levels, i.e. in the adventitia of the popliteal artery, but they may also occur in the common femoral artery adjacent to the hip joint along the iliofemoral axis, in locations near the elbow or the wrist, and in veins.5 A total of 45 extrapopliteal localisations have been described. These extrapopliteal locations account for 20–25% of all cases of adventitial cystic disease. Carlsson et al.6 have also observed adventitial cystic disease in the common femoral artery.

[Q2: B, D, G]

Fig. 24.6  The wall of the cyst covered on the inside by a single interrupted or several layers of cuboid cells akin to synovial mesothelium

Fig. 24.7  Cross-section through an artery with a large adventitial cyst and compression of the arterial lumen of the resected popliteal artery

Because of the sometimes varying degree of intermittent claudication or occasional disappearance of symptoms, the disease can be mistaken for a popliteal entrapment syndrome. Noninvasive techniques have vastly improved diagnosis. Duplex coloured scanning followed by T2-weighted MRI now appear to be the best choice. Both methods are capable of visualisingthecystsurroundingthepoplitealarteryandrulingoutthepoplitealentrapmentsyndrome.4 Koppensteiner et al.7 have shown that intravascular ultrasound imaging can reliably identify

adventitial cystic disease as well. Digital subtraction angiography is necessary to define the degreeofstenosisorthelengthofocclusion.Stenoticlesionshaveanhourglassappearanceor present with a semilunar impression (the scimitar sign).4 [Q3: A, C, E, G, H]

The treatment options depend on the degree of stenosis and whether the popliteal artery is occluded. In the case of total occlusion, most authors have resorted to total resection of the affectedpoplitealarterialsegmentwithinterpositioneitherofautologousveinorring-enforced polytetrafluoroethylene (PTFE) grafts. The initial success rate is reportedly almost 90%.4

If the cyst lies within the adventitia and surrounds and compresses the artery without having given rise to total occlusion, as in our second case, then the artery does not have to be resected if the cyst can be removed entirely.1 Partial removal of the cyst is thought to bear the risk of recurrence.1 If a connecting stem usually accompanied by a small collateral artery is present, thenthis shouldberesectedat the level of the kneecapsule toavoidrecurrence.2 The initial success rate in 68 cases treated accordingly is 94%4; in our own experience, it was successful in case 2 described above.1

There is the possibility of resecting only part of the artery, e.g. the medial vascular aspect that bears the cyst, and then replacing the wall defect with a vein patch. This approach has been used in a small number of patients, with success in three of four cases.4 Percutaneous transluminal angioplasty (PTA) has been performed just once, and failed. PTA should therefore probably be discarded as an treatment option.

An interesting series of seven cases has been reported by Do et al.8 They forwarded a 14-gauge needle with real-time ultrasonic guidance transcutaneously directly into the cyst and aspirated its contents in cases presenting with stenosis only (but not in the presence of total occlusion). This was carried out on an outpatient basis, with a 100% success rate. Follow-up colour duplex sonography performed between 1 and 32 months after the procedure showed no recurrent stenosis.8

While the method of percutaneous aspiration of a popliteal cyst guided by ultra-sonog- raphy is appealing because it can be done on an outpatient basis and mini-invasively, the question of recurrence is not settled since the cyst remains in place; hence the capacity to form mucinous substance remains and with it the possibility of recurrence. Although Do et al. know of no recurrence in their cases followed up for 1–32 months, there is a definite need for a more systematic long-term follow-up, which should be conducted in all cases in which the cyst has not been removed by resection.

There is the occasional report of percutaneous clot lysis of occluded popliteal arteries followed by aspiration of the contents of the cysts. This method was reported by Samson and Willis9 to be successful, but its reliability has not been proven by others. There is hardly a valid contraindication against surgical removal of an occluded popliteal segment in the presence of occlusion, and this is probably the method of choice that offers the greatest chances for complete recovery.

Finally, there are reports of spontaneous resolution of the popliteal cysts.10, 11 It must be assumed, therefore, that occasionally cysts can burst or their contents escape into the periarticular space. This mechanism has been surmised by Soury et al.10

In conclusion, the treatment of choice remains surgical resection, either of the cyst alone if it surrounds the artery or of the occluded segment if total occlusion and appositional thrombosishasoccurred.Inthiscase,veingraftinterpositionshouldbeperformed.Inexpert hands, percutaneous transluminal aspiration has been shown to be efficacious. [Q4]