Annals of Vascular Surgery
Volume 24, Issue 8 , Pages 1135.e13-1135.e18, November 2010

Massive Aneurysm in a Persistent Sciatic Artery

  • Benjamin Charles Knight

      Affiliations

    • Corresponding Author InformationCorrespondence to: Benjamin Charles Knight, Department of Vascular Surgery, North Manchester General Hospital, Delaunays Road, Crumpsall, Manchester, M8 5RB. United Kingdom
    • ,
  • William F. Tait

Department of Vascular Surgery, North Manchester General Hospital, Manchester, United Kingdom

published online 04 August 2010.

Article Outline

Persistent sciatic artery (PSA) is an exceptionally rare embryological vascular anomaly with a reported incidence, based on angiographic series, of between 0.01 and 0.05%. We report a case of a patient with bilateral PSAs and a unilateral 12-cm aneurysm arising from the left PSA. As with our case, most PSAs are among the dominant arteries that supply blood to the lower limb with aneurysm formation occurring in up to 40% of cases. The femoral artery is often hypoplastic. Presentation usually includes symptoms and signs of an enlarged buttock mass, sciatic nerve compression, and distal limb ischemia. An interposition inlay graft is the preferred method of surgical repair. Dissection of the aneurysm is not recommended because of risk of damage to the sciatic artery. Endovascular stent placement is an accepted method of repair but does not deal with any local symptoms of the expanding aneurysm.

 

A persistent sciatic artery (PSA) is an exceptionally rare embryological vascular anomaly with a reported incidence, based on angiographic series, of between 0.01 and 0.05%.1, 2, 3 The occurrence of PSA was first described by Green in 1832 and published in the Lancet.4 A PSA is prone to arteriosclerosis and vessel wall degeneration, and PSA aneurysms have been reported in 25–40% of cases.5, 6 In 1994, a comprehensive review of the world literature reported 77 (46%) episodes of aneurysm formation in 167 cases of PSA.7 We present a massive aneurysm formation in a patient with bilateral PSAs and review the current literature with regard to etiology, embryology, presentation, and management. To our knowledge, this is the largest PSA aneurysm reported in the medical literature.

Back to Article Outline

Case Report 

A 39-year-old woman presented to her general practitioner with a 3-month history of sciatica in the left leg and foot drop. Significant medical history included HIV infection and previously treated pulmonary tuberculosis. A large semi-solid swelling in the left gluteal region was noted, suspicious of a cold tuberculosis abscess. Physical examination revealed a tender, pulsatile 12 cm mass in the left gluteal region. All distal pulses in the right lower extremity were present and normal. A normal femoral pulse on the left was palpated; however, distal pulses were absent. Magnetic resonance imaging and lower limb angiography revealed bilateral complete PSAs and confirmed the presence of a 12-cm aneurysm arising from the PSA on the left side (Fig. 1, Fig. 2). Elective repair of the PSA aneurysm was undertaken. The patient was placed in a supine position and an oblique incision in the left iliac fossa was made. A dose of 5,000 IU of unfractionated heparin was administered to the patient. The internal and external iliac arteries were controlled through a retroperitoneal approach. The patient was then placed in the right lateral position. A modified curvilinear incision sweeping over the left buttock was made (Fig. 3).

  • View full-size image.
  • Fig. 1 

    A Angiogram showing bilateral persistent sciatic arteries and early blush of aneurysm in a patent left sciatic artery. B Left sciatic artery aneurysm with a hypoplastic superficial femoral artery.

  • View full-size image.
  • Fig. 3 

    A Landmarks used to accurately place incision to gain access to sciatic artery. B Gluteus maximus lid retraction to illustrate exposure to the sciatic neurovascular bundle.

The purpose was to release the gluteus maximus caudally, and then release its attachment from the femur and iliotibial tract, and finally reflect the muscle belly medially to gain access to the sciatic vessel. The gluteus had atrophied to such a degree that this was not necessary and was easily split in the line of its fibers and retracted. The aneurysm was exposed and the sac opened (Fig. 4). The proximal and distal ends of the PSA were identified and an inlay reversed long saphenous vein graft was closed in place with 5/0 prolene sutures (Fig. 5). The exposed sac and clot were excised and histological analysis revealed an inflammatory sac with a necrotic arterial wall and no evidence of neoplasia (Fig. 6). The results for the cultures for Mycobacterium tuberculosis were found to be negative. Cell salvage was used during the procedure. A total blood loss of 544 mL was incurred, with 69 mL of packed cells transfused back to the patient at the end of the procedure.

The patient made an uneventful recovery and was discharged home on day 7. She remains well 6 months postoperatively, with no evidence of recurrent aneurysm, lower limb ischemia, or sciatic nerve damage.

Back to Article Outline

Discussion 

Embryology 

The axial artery is the major blood supplier to the lower limb at the 9-mm stage in embryological development. The axial artery is a direct continuation of the internal iliac artery, which in turn originates from the umbilical artery. As fetal development progresses, the definitive blood supply to the limb is taken over by the external iliac artery which develops from the fifth lumbar intersegmental artery. By the 22-mm stage, the axial artery almost entirely regresses but persists as three remnants: the sciatic artery (ischiatic artery), a segment of the popliteal artery, and a segment of the peroneal artery.8 Failure of either the axial artery to involute or the femoral system to develop leads to a persistent sciatic artery5 which follows the course of the sciatic nerve and occasionally lies within the nerve sheath.3

Anatomy 

A PSA exists in two distinct forms: complete and incomplete (Fig. 7). In a complete PSA, the sciatic artery is the dominant blood supplier to the limb and it has continuity from the internal iliac artery to the popliteal artery. The superficial femoral artery (SFA) is hypoplastic and terminates in the mid thigh. This is the more common variant and occurs in 70–80% of PSAs.5, 6 In an incomplete PSA, the SFA remains the dominant blood supplier to the lower extremity, with the PSA becoming hypoplastic in the mid thigh.5

  • View full-size image.
  • Fig. 7 

    Embryology of a persistent sciatic artery. Left—Normal anatomy. Shaded areas represent remnants of the sciatic artery. Middle—Incomplete variant. Persistent sciatic artery is hypoplastic and terminated in the mid-thigh. Collaterals with the popliteal may exist. Colored area indicates main blood supply to limb. Right—Complete variant. superficial femoral artery is hypoplastic and terminates in mid-thigh. Collaterals with popliteal may exist. Colored area indicates main blood supply to limb.

Etiology 

Recognition of a PSA aneurysm is essential as patients commonly present with symptoms of distal limb ischemia which may result in an incorrect diagnosis of SFA occlusive disease and occasionally inappropriate revascularisation.6 The etiology of aneurysm formation within a PSA is unclear. External compression, given its exposed position or damage to the artery during hip flexion against the piriformis muscle and sacrospinous ligament has been implicated.9 Others believe that there may be an inherent collagen defect within the arterial wall.5 Clarke and Beazley10 noted that all three previous PSA aneurysms had positive serological markers for syphilis. Subsequent analysis of the tissue proved negative for spirochetes but this theory has almost been abandoned. Approximately 50% of all PSAs are found incidentally and 50% are bilateral.3, 6, 11 PSA aneurysms associated with internal iliac artery aneurysm and with limb shortening and hemihypertrophy of the leg or pelvis have been reported.3, 12, 13 The largest previously reported sciatic artery aneurysm measured 7 cm in diameter. To our knowledge, our case represents the largest PSA reported in the medical literature.14 It is also the only case described using cell salvage in a patient with HIV infection.

Presentation 

Similar to other arterial aneurysms, PSA aneurysms are susceptible to thromboembolic events and distal ischemia and they commonly present in this way.15 Like other aneurysms, they may rupture, although this occurs rarely. Because of their location in the buttock region, they can present with signs secondary to local compression and irritation of the sciatic nerve.13, 16 This may manifest as lower motor nerve weakness, sensory deficit, or pain in the distribution of the sciatic nerve. PSA aneurysms also commonly present as a pulsatile mass in the buttock; in the extensive series performed by Williams et al.,12 31% of cases presented as a pulsatile mass in the buttock. However, these can easily be missed as the patients often do not allude to its presence or may be obese with a small aneurysm. Differential diagnoses include a gluteal artery aneurysm, an arteriovenous malformation, soft-tissue neoplasms, and infection.5, 17

Management 

Most incidental PSAs do not require treatment; however, all PSA aneurysms should be treated because they involve a high risk of complications, as discussed previously. Treatment essentially depends on whether the PSA is complete or incomplete and on the patient's symptoms. Several techniques have been described in the medical literature. Ligation of the aneurysm may be appropriate in patients with unsalvageable limbs or in those with the incomplete type of PSA. Proximal and distal ligation is preferable as proximal ligation rarely caused thrombosis in the aneurysm alone.5 In the same subgroup of patients, embolization of the aneurysm has also been successfully used to occlude a PSA aneurysm.18, 19

Often revascularization is required as the hypoplastic femoral vessel (seen in the complete variant) is unable to sustain adequate blood flow to the extremity. Various approaches have been described. After ligation of the aneurysm, revascularization has been achieved with interposition grafts between the internal iliac artery and popliteal/distal sciatic artery, the so called obturator bypass.15, 20 Alternatively, many surgeons have chosen to revascularize with a femoral-popliteal bypass (assuming that the proximal femoral artery is adequate) because of the familiarization with this approach.3, 13 Interestingly, Ertuk and Tatli16 reported a case in which a femoral to anterior tibial bypass was performed, followed by successful coil embolization of the aneurysm. However, interposition grafting has become more popular recently as it allows exclusion of the aneurysm, restoration of circulation, and preserves the femoral vessels in case future surgery is required; it was the chosen method of repair in our case.5, 6, 19, 20 Concerns over graft compression in the buttock have been described and hence was in vogue earlier for the obturator bypass technique as it negates this potential complication. It was of concern that placing a graft in such a vulnerable position would lead to graft occlusion and that by keeping the PSA in circulation it would be vulnerable to further degeneration of the vessel wall, these concerns proved to be unfounded. To our knowledge, this complication has only been reported once in the previously published data.21 Dissection and then excision of the aneurysm from the sciatic nerve is not recommended because of a high risk of damage to the nerve.10

A combination of open surgery and interventional radiology has also been described. Becquemin et al.22 ligated a PSA aneurysm in the mid thigh and performed a standard femoral popliteal bypass. Following this, the opposite groin was used to place a Fogarty balloon catheter distal to the aneurysm and then definitively embolize the aneurysm. This technique allows for minimal dissection around the aneurysm and theoretically reduces the risk for sciatic nerve damage which is often in close proximity.5, 22

More recently, PSA aneurysms have successfully been treated through the endovascular approach.14, 23 Fearing et al.14 used a distal medial thigh approach to gain access to the distal sciatic artery and feed an endovascular stent proximally into the aneurysm. This has the added advantage of limiting potential damage to the sciatic nerve; however, it has its own unique complications such as endoleak and stent migration. This was considered initially in our case but the massive size of the aneurysm and presence of foot drop necessitated surgical intervention.

Back to Article Outline

Conclusion 

During assessment of any patient presenting with signs and symptoms of distal limb ischemia, anatomical and embryological anomalies must be considered, such as a persistent sciatic artery, in which aneurysmal dilatation is common place. Failure to do so may result in an inappropriate vascular revascularization operation. Proximal and distal ligation is appropriate for an incomplete PSA aneurysm, whereas aneurysm exclusion and revascularization is recommended for a complete PSA. Good results can be achieved with interposition grafting, with minimal complications.

Back to Article Outline

References 

  1. Greebe J. Congenital anomalies of the iliofemoral artery. J Cardiovasc Surg (Torino). 1977;18:317–323
  2. de Boer MT, Evans JD, Mayor P, Guy AJ. An aneurysm at the back of a thigh: a rare presentation of a congenitally persistent sciatic artery. Eur J Vasc Endovasc Surg. 2000;19:99–100
  3. Mayschak DT, Flye MW. Treatment of the persistent sciatic artery. Ann Surg. 1984;199:69–74
  4. Green P. On a new variety of the femoral artery. Lancet. 1832;1:730–731
  5. Brantley SK, Rigdon EE, Raju S. Persistent sciatic artery: embryology, pathology, and treatment. J Vasc Surg. 1993;18:242–248
  6. Wolf YG, Gibbs BF, Guzzetta VJ, Bernstein EF. Surgical treatment of aneurysm of the persistent sciatic artery. J Vasc Surg. 1993;17:218–221
  7. Ikesawa T, Naiki K, Moriura S, Ikeda S, Hirai M. Aneurysms of persistent sciatic arteries with ischaemic complications: case report and review of the world literature. J Vasc Surg. 1994;20:96–103
  8. Larson WJ. Human Embryology. 2nd ed.. New York, NY: Churchill Livingstone; 1997;203-204
  9. Fagge CH. Case of Aneurism, seated on an abnormal main artery of the lower limb. Guy's Hosp Rep. 1864;10:151–159
  10. Clark FA, Beazley RM. Sciatic artery aneurysm: a case report including operative approach and review of the literature. Am Surg. 1976;42:13–16
  11. Martinez LO, Jude J, Becker D. Bilateral persistent sciatic artery. A case report. Angiology. 1968;19:541–548
  12. Williams LR, Flanigan DP, O'Connor RJ, Schuler JJ. Persistent sciatic artery. Clinical aspects and operative management. Am J Surg. 1983;145:687–693
  13. Batchelor TJ, Vowden P. A persistent sciatic artery aneurysm with an associated internal iliac artery aneurysm. Eur J Vasc Endovasc Surg. 2000;20:400–402
  14. Fearing NM, Ammar AD, Hutchinson SA, Lucas ED. Endovascular stent graft repair of a persistent sciatic artery aneurysm. Ann Vasc Surg. 2005;19:438–441
  15. Urayama H, Tamura M, Ohtake H, Watanabe Y. Exclusion of a sciatic artery aneurysm and an obturator bypass. J Vasc Surg. 1997;26:697–699
  16. Erturk SM, Tatli S. Persistent sciatic artery aneurysm. J Vasc Interv Radiol. 2005;16:1407–1408
  17. Meek GN, Hill RL. Surgical treatment of gluteal artery aneurysms. Am J Surg. 1968;116:731–734
  18. Loh FK. Embolization of a sciatic artery aneurysm an alternative to surgery: a case report. Angiology. 1985;36:472–476
  19. Kubota Y, Kichikawa K, Uchida H, et al. Coil embolization of a persistent sciatic artery aneurysm. Cardiovasc Intervent Radiol. 2000;23:245–247
  20. Hutchinson JE, Cordice JW, McAllister FF. The surgical management of an aneurysm of a primitive persistent sciatic artery. Ann Surg. 1968;167:277–281
  21. Blumberg L, Grant C. Bilateral persistent primitive sciatic artery with unilateral aneurysm and limb ischaemia. J R Coll Surg Edinb. 1985;30:321–323
  22. Becquemin JP, Gaston A, Coubret P, Uzzan C, Melliere D. Aneurysm of persistent sciatic artery: report of a case treated by endovascular occlusion and femoropopliteal bypass. Surgery. 1985;98:605–611
  23. Gabelmann A, Krämer SC, Wisianowski C, et al. Endovascular interventions on persistent sciatic arteries. J Endovasc Ther. 2001;8:622–628

PII: S0890-5096(10)00270-0

doi:10.1016/j.avsg.2010.05.017

Annals of Vascular Surgery
Volume 24, Issue 8 , Pages 1135.e13-1135.e18, November 2010

Article Tools

* Image Usage & Resolution