Idiopathic iliac arterial aneurysms in a child

Arterial aneurysms are very rare in children, especially those who have no history of cardiac or vascular malformation, connective tissue disorder, or trauma. We describe a 3-year-old boy who had multiple arterial aneurysms of the left external iliac artery with a maximal diameter of 67 mm, with no history of these disorders. The iliac artery distal to the aneurysm and superficial femoral artery were occluded causing the growth disturbances of his left leg. He underwent graft replacement of the left iliac artery using a ringed Gore-Tex graft (6 mm in diameter). Postoperative angiogram showed a patent graft without any residual aneurysm in the left iliac artery. His ankleibrachial index improve from 0.2 to 0.6 after surgery.

Percutaneous treatment of iliac aneurysms and pseudoaneurysms with Cragg Endopro System 1 stent-grafts

PURPOSE

To evaluate the feasibility and short-term follow-up results of treating iliac aneurysms by the Cragg Endopro System 1 stent-graft.

METHODS

Nine lesions (two pseudoaneurysms and seven atherosclerotic aneurysms) were treated in eight patients by percutaneous implantation of a total of 10 stent-grafts. The procedure was followed by anticoagulation with heparin for 6 days, then antiplatelet therapy. Follow-up was by color Doppler ultrasound scan at 2 days and 3 months after the procedure for all patients, and by venous digital subtraction angiography and/or angio-CT up to 12 months later for four patients.

RESULTS

Initial clinical success rate was 100% and there were two minor complications. In one case the delivery system was faulty resulting in failure to deploy the stent-graft. An additional device had to be used. At 3-12 months all prostheses were patent but one patient (12.5%) had a minimal pergraft leak.

CONCLUSION

Percutaneous stent-grafting with this device is a safe and efficacious treatment of iliac artery aneurysms.

Screening for abdominal aortic aneurysm during transthoracic echocardiography in a hypertensive patient population

This study was undertaken to determine the utility of transthoracic echocardiography as a screening test for occult abdominal aortic aneurysm in hypertensive patients older than 50 years of age. Longitudinal and transverse images of the abdominal aorta were obtained during the subcostal portion of the transthoracic echocardiogram. Abdominal aortic aneurysm was defined as an abdominal aortic dimension (antero-posterior or lateral) > or = 3.0 cm. Exclusion criteria included prior abdominal aortic aneurysm repair, known abdominal aortic aneurysm, or inadequate images of the abdominal aorta (nine patients). Two hundred patients (107 men, 93 women; mean age 71 years, range 51 to 92 years) met the study inclusion criteria. An occult abdominal aortic aneurysm was identified in 13 patients (6.5%). Sixty-nine percent of the abdominal aortic aneurysm patients were men, with a mean age of 73 years and a mean duration of hypertension of 11 years. Seventy-seven percent had a history of tobacco use, and 15% had a positive family history of abdominal aortic aneurysm. All aneurysms were infrarenal in location, with abdominal aortic aneurysm diameter ranging from 3.0 to 5.2 cm (mean 3.9 cm). Laminated thrombus was present in six patients (46%), and in one patient a right common iliac artery aneurysm was also detected. Imaging of the abdominal aorta during transthoracic echocardiography required an average of 6.7 minutes (range 4 to 10 minutes). In conclusion, the abdominal aorta could be accurately imaged in the majority of patients (96%) undergoing transthoracic echocardiography in this study. The incidence of occult abdominal aortic aneurysm in hypertensive patients older than 50 years of age is significant (6.5%). Screening for occult abdominal aortic aneurysm in this patient population should be a routine extension of the transthoracic echocardiogram.

Endovascular grafts for noninfected aortoiliac anastomotic aneurysms

PURPOSE

This report describes our experience with endovascular repair of aortic and iliac anastomotic aneurysms.

METHODS

Between June 1994 and March 1996, 12 noninfected aortic or iliac anastomotic aneurysms in 10 patients who had serious comorbid medical conditions that precluded or made difficult standard operative repair were treated using endovascular grafts. No patient in this study had a history of fever, leukocytosis, or computed tomographic evidence of a periprosthetic fluid collection that was suggestive of infection of the original graft. Endovascular grafts composed of polytetrafluoroethylene and balloon-expandable stents were introduced through a femoral arteriotomy and were placed using over-the-wire techniques under C-arm fluoroscopic guidance.

RESULTS

Endovascular grafts were successfully inserted in all patients with aortic or iliac anastomotic aneurysms. There were no procedure-related deaths, and complications included one postprocedure wound hematoma and one perioperative myocardial infarction. Graft patency has been maintained for a mean of 16.1 months, with no computed tomographic evidence of aneurysmal enlargement or perigraft leakage.

CONCLUSIONS

Endovascular grafts appear to be a safe and effective technique for excluding some noninfected aortoiliac anastomotic aneurysms in high-risk patients and may become a treatment option in all patients who have clinically significant lesions.

Morphologic assessment of abdominal aortic aneurysms by spiral computed tomographic scanning

PURPOSE

The aim of this study was to seek a relationship between the morphologic features of abdominal aortic aneurysms and the feasibility of endoaortic grafting.

METHODS

Between June 1995 and January 1996, 86 patients were prospectively studied with contrast-enhanced spiral computed tomographic scans, which provided 35 parameters concerning the aorta and iliac arteries. Four groups were established according to the diameter of abdominal aortic aneurysms: group A, 40 to 49 mm, 36 patients; group B, 50 to 59 mm, 26 patients; group C, 60 to 69 mm, 10 patients; and group D, greater than 70 mm, 14 patients.

RESULTS

There was a correlation between the diameter and length of the aneurysm (p < 0.0001) and between aneurysm diameter and length of the proximal neck (p < 0.001). Presence of a proximal neck or a distal neck was more frequent in groups A and B than in groups C and D (p < 0.01). The feasibility of endovascular grafting was estimated at between 50% and 61.6% and was higher in groups A and B than in groups C and D (p < 0.01).

CONCLUSIONS

This study has shown an inverse relationship between the diameter of the aneurysm and the length of the aortic neck (correlation coefficient, -0.3640, p < 0.001). The diameter of an aneurysm was the most useful of the 31 parameters measured in predicting the feasibility of endoaortic grafting, estimated at 71% for aneurysms less than 60 mm in diameter and 37.5% for aneurysms greater than 60 mm in diameter (p < 0.01).

Three-year experience with the White-Yu Endovascular GAD Graft for transluminal repair of aortic and iliac aneurysms

PURPOSE

To report a > 3-year experience with a modular, balloon-expandable endovascular graft used for aneurysm exclusion in the aorta and other arteries.

METHODS

The customized White-Yu Endovascular GAD Graft, a woven polyester prosthesis with an intrinsic Elgiloy wire graft attachment system along the body of the graft, is a flexible endograft design available in straight, tapered, and bifurcated versions that can be delivered transluminally through 18F to 24F sheaths.

RESULTS

Since July 1993, 93 patients have received the White-Yu endograft for treatment of 76 abdominal aortic, 3 thoracic aortic, 13 iliac, and 1 popliteal aneurysms. Of the 79 aortic procedures, 39 involved straight tube grafts, 20 were tapered aortoiliac models, and 20 were bifurcated devices. Success rates for tube grafts were 81% in the abdominal aorta and 100% for the thoracic aorta; 5 primary endoleaks (14%) and 2 conversions to surgery (5.6%) occurred with this graft type. Aortoiliac grafts were deployed successfully in 95% (19/20) of cases with 1 conversion (5%) due to thrombosis. Seventy-five percent of the bifurcated endograft procedures were successful, with 4 conversions (20%) for technical failures and 1 graft thrombosis. Four additional endografts were deployed to treat two primary and two secondary endoleaks in tube graft patients. Two access-related arterial injuries were treated surgically. There was one case of embolus to the distal femoral artery but no microembolization. Overall perioperative (30-day) mortality was 3.1%. Over a mean 18-month follow-up (range 2 to 39), no late graft thrombosis, stenosis, or graft migration has been seen on CT scans or X ray. Endoleak has not been detected in any aortoiliac or bifurcated graft. Aneurysm size has diminished consistently in successfully treated cases.

CONCLUSIONS

The White-Yu endograft appears to offer a safe, efficacious, and minimally invasive means of excluding aneurysms from the circulation. Improvements in patient selection, surgical techniques, and equipment have reduced the incidence of endoleak and conversion to open repair over the course of the evaluation.

Endovascular repair of peripheral aneurysms, pseudoaneurysms, and arteriovenous fistulas

Endovascular repair of peripheral arterial lesions was performed in 10 patients including two iliac aneurysms, two iliac anastomotic pseudoaneurysms, one subclavian pseudoaneurysm, one axillary anastomotic disruption, two prosthetic pseudoaneurysms, and two posttraumatic arteriovenous (AV) fistulas. The indications for repair were aneurysm size in five cases, massive hematoma in one, threatened prosthetic dialysis graft in two, venous hypertension with non-healing ulcer in one, and arm pain in one. Vascular access was obtained through surgical cutdown in all cases, via the femoral artery in five patients, the proximal brachial artery in three and a prosthetic graft in two. Stented prosthetic grafts were used in five cases (1 polyester and polytetrafluoroethylene 4 [PTFE]), and PTFE-covered stents in five cases. Concomitant procedures were done in four patients including two open repairs of a common femoral artery aneurysm, a transluminal dilatation of a proximal aortic anastomotic stenosis, and an iliac artery transluminal angioplasty. Eight of 10 cases were technically successful. Completion arteriography revealed complete exclusion of all lesions, except for one minimal proximal stented graft leak in a pseudoaneurysm, and an incomplete obliteration of an AV fistula. No complications occurred. Operative time ranged from 45 min to 5 hours. Postoperative hospital stay was 1 day in five patients, 2 days in three patients, and 4 days in two patients. Follow-up contrast CT scan, arteriography, or duplex scanning demonstrated complete exclusion of all lesions except an AV fistula, and decrease in size in three aneurysms. The proximal leak initially present in a stented graft resolved. All grafts and covered stents remained patent at 2-19 months of followup. Endovascular exclusion of peripheral arterial aneurysms, pseudoaneurysms, and AV fistulas can be done with a high degree of technical success, low morbidity, and short hospital stay. Short-term follow up is encouraging, however, long term follow up of these procedures is warranted to assess durability of the repair and absence of complications.

Three-dimensional reconstruction of an iliac artery aneurysm in a man with obstructive uropathy

Reconstruction of three-dimensional images is performed either by scanner-based systems or by independent computers. The advantages of a stand-alone system include compatibility with multiple imaging modalities, more advanced technology, and increased user interaction. This report illustrates the use of a stand-alone system for the less commonly utilized purpose of three-dimensional reconstruction of abdominal soft tissues. It further demonstrates the merit of three-dimensional imaging as an important diagnostic adjunct and as a valuable source of preoperative surgical information.

Morphometry and classification in abdominal aortic aneurysms: patient selection for endovascular and open surgery

PURPOSE

To evaluate the anatomic morphology of abdominal aortic aneurysms (AAAs) and compose a classification system to facilitate patient selection for endovascular graft (EVG) repair.

METHODS

Data on 242 consecutive AAA patients evaluated on a nonemergent basis in a 3.5-year period to July 1996 were prospectively entered into a registry. Patients were examined using sequential intravenous spiral computed tomographic angiography and intraarterial digital subtraction angiography. The data collected and analyzed included: diameters of the supra- and infrarenal aorta, aneurysm, aortoiliac bifurcation, and iliac arteries; lengths of the proximal neck, distal cuff, and aneurysm; degrees of iliac artery tortuosity; and occlusion of the visceral, renal, or iliac arteries.

RESULTS

The 242 aneurysms could be easily grouped into three distinctive categories related to the extent of the aneurysmal disease. Type I AAAs (11.2%) had nondilated, thrombus-free infrarenal (15 mm) necks and distal (10 mm) cuffs appropriate for EVG anchoring. In type II and its subgroups (72.3%), a sufficient proximal neck was present, but the aneurysm extended into the iliac arteries; 56% of these were eligible for a bifurcated endograft. In type III (16.5%), a sufficient proximal neck was missing, independent of distal involvement. In all, 51.7% were good EVG candidates based on AAA morphology. Taking into consideration relevant concomitant vascular diseases, proximal iliac kinking, and iliac, renal, or visceral occlusive disease, only 30.2% of the population were potential candidates for an efficient and secure EVG repair using the devices currently available.

CONCLUSIONS

In contrast to classical open repair, detailed preoperative measurements are recommended for EVG planning. The use of liberal EVG indications may lead to a higher incidence of complications, whereas restrictive morphology-based selection criteria may offer excellent results.

Arteriomegaly and inflammatory abdominal aortic aneurysm. Case report

In this case report inflammatory abdominal aortic aneurysm (IAAA) was superimposed on an arteriomegaly condition complicated by bilateral aneurysm of the common iliac arteries. Obstruction of the right ureter, mild hydronephrosis of the left system and a slight impairment of renal function were also present. Preoperative cellular and humoral immunological parameters were within normal limits while the erythrocyte sedimentation rate (ESR) was elevated (74 mm). Histological analysis showed numerous scattered lymphoid cells or organized in follicles with germinal centers within the adventitial thickening of the IAAA wall. Immunohistochemical analysis on frozen sections demonstrated that dispersed and perivascular lymphoid cells were mainly composed of similar amounts of CD3+/CD4+ and CD3+/CD8+ T lymphocytes. Histological analysis of the common iliac artery aneurysm showed a mild intimal thickening will small aggregates of macrophages. After aneurysm repair all peripheral blood analysis normalized within one month after surgery. The IAAA observed in our patient with arteriomegaly as underlying arterial disease cannot be interpreted as an inflammatory variation of an atherosclerotic aneurysm. The histological pattern of the inflammatory reaction and its resolution after surgery give, in our opinion, more credit to the etiopathogenetic hypothesis of a reaction elicited by an antigen within the arterial wall of the infrarenal aorta which might be enhanced by the lymphatic stasis subsequent to aneurysm compression.

A self-expanding endoluminal graft for treatment of aneurysms: results through the development phase

BACKGROUND

The results of two and a half years' experience of endoluminal treatment of aneurysmal disease (from March 1993 to December 1995) are reported.

METHODS

The endoluminal grafts were individually made at Royal Perth Hospital. They are based on Dacron-covered stainless steel self-expanding 'Z' stents with Gianturco barbed stents (Cook Pty, Australia) for proximal anchorage for grafts within the aorta.

RESULTS

Fourteen straight tube grafts (nine for aortic aneurysm, four for iliac aneurysm and one for subclavian aneurysm) and 24 bifurcate grafts were deployed; all were in patients considered high-risk for conventional repair. Seventy-two per cent of the straight tube grafts successfully excluded the aneurysm. The bifurcate grafts, in use since July 1994, successfully excluded the aneurysm in 88%. There were two delayed deaths from rupture after the grafts failed to exclude the aneurysms; two patients required conversion to open repair and survived; three patients have persistent endoleaks; and three of the bifurcate grafts subsequently occluded a graft limb but did not require further intervention. Ninety per cent of these complications occurred in the first half of the series (prior to January 1995).

CONCLUSIONS

A learning and development curve was clearly apparent. The results thereafter compare favourably to those for open repair in similar high-risk groups, suggesting that these techniques hold promise for all patients with aneurysms.

[Diagnosis using x-ray computed angiotomography of an iliac artery aneurysm in an infant]

The authors describe an infant with an aneurysm of the right iliac artery, associated with three sites involving the inferior mesenteric artery and its first two branches, most likely related to an episode of chicken pox. Helical angiography with computed tomography, performed with a continuous-rotation scanner, allowed precise assessment of the lesions, in particular those affecting the inferior mesenteric artery.

[Aorto-iliac aneurysms and associated gastrointestinal neoplasms. Treatment problems]

In patients affected by aortoiliac aneurysm the concurrent presence of a gastrointestinal tumor is a not infrequent occurrence which poses problems of therapeutic approach (one step operation or prior treatment of one of the two diseases; in the latter case definition of timing and sequence of the surgical treatment). Three cases are reported where an eclectic therapeutic approach has enabled satisfactory results. A patient with an isolated aneurysm of right hypogastric artery associated with rectal cancer was treated with percutaneous embolization of the aneurysm and subsequent excision of the tumor. In a patient with a neoplasm of the left colon and aortic aneurysm, the aneurysm was treated first and after about a month the tumor was resected. In a patient with gastric cancer and aortic aneurysm subtotal gastrectomy was first performed and subsequently, after about 3 months, the aneurysm was treated by extraperitoneal route. Even if an unidirectional approach cannot be defined, it is thought that the two-step treatment of the associated diseases is preferable. In the presence of non stenosed non bleeding colorectal tumors it seems more suitable to treat the aneurysm first (increased postoperative risk for rupture of the aneurysm; more difficult preparation of subrenal aorta in the presence of cicatricial outcomes of colonic surgery; persistence of perianastomotic infections after colonic resection). Gastric tumors should be treated first for their higher biological aggressiveness and unfeasible correct preoperative staging. In particular cases (single unilateral aneurysm of a hypogastric artery associated with gastrointestinal cancer), non surgical treatment of the vascular lesion (embolization during angiography) is the treatment of choice.

Percutaneous transluminal treatment of an iliac pseudoaneurysm with endoprosthesis implantation. A case report

PURPOSE

Evaluation of a covered stent in the treatment of an iliac pseudoaneurysm.

MATERIAL AND METHODS

During PTCA, a 61-year-old man with angina pectoris was shown to have an asymptomatic pseudoaneurysm, 5 x 4 x 4 cm, of the left common iliac artery (CIA). The patient was not a candidate for surgery. The pseudoaneurysm was treated by insertion of a covered stent (8 mm/6 cm).

RESULTS

By 30 s after stent placement, the pseudoaneurysm was angiographically excluded. Twelve and 17 months after stent implantation, the patient had no symptoms from the lower extremities and the left CIA was open with normal flow in the stent.

CONCLUSION

Our case illustrates the ability of a covered stent to exclude a pseudoaneurysm. Percutaneous intravascular stent placement in the management of iliac pseudoaneurysms might be the treatment of choice in patients with increased risk of major anesthesia and surgery.

[Percutaneous treatment of iliac aneurysms with endovascular stented grafts]

Two cases of iliac aneurysms treated percutaneously by endovascular stented graft are reported. The initial radiographic evaluation included arteriography and computed tomography with helical acquisition and three dimensional reconstruction. This enabled analysis of the flow path, the extent of the wall thrombus, the choice of stent graft's size. The procedure of implantation was technically trouble free. The post-procedure arteriography and 3D CT demonstrated occlusion of the aneurysm and restauration of a normal flow path. The three, six and twelve month check-ups confirm the good results. In weakened patients or those not requiring aorto-iliac surgery, percutaneous treatment of iliac aneurysm can be carried out easily. The contribution of 3D CT is essential in assessing the endo- and extra-luminal characteristics of aneurysm for indicating the percutaneous route and selecting size of the stented graft.

Endovascular repair of iliac artery aneurysm with Endoprosystem I: a multicentric French study

Due to their position deep in the pelvis, the classical surgical treatment of iliac artery aneurysm leads to a high morbidity and mortality rate. The transfemoral percutaneous repair of these aneurysms is now possible thanks to a new device the endoprosystem I from "Mintech". We began in 1994 a study including radiological, cardiac and vascular centers all of them skilled in endovascular procedures. 27 patients entered the study: 1 patient died, 2 attempt failed and 2 presented leakage: the immediate failure rate was then 18.5%. For the late result (min 6, Max 19, mean 12 months) we had 1 thrombosis treated by surgery, 1 restenosis treated by PTA. We did not see any polyester dilatation or reactivation of aneurysm at the scan control at one year. We conclude that the percutaneous treatment of iliac aneurysm is possible and safe but we need long term result to validate the method.

Results of endoluminal grafting of abdominal aortic aneurysms are dependent on aneurysm morphology

The aim of this prospective study was to analyze the outcome of elective endoluminal grafting in patients with various morphologies of abdominal aortic aneurysms (AAA). Between May 1992 and May 1994, endoluminal repair of AAA was undertaken in 40 patients. After detailed imaging by means of CT scanning and arteriography, aneurysms were classified into one of two types according to the following criteria: type I (suitable for transfemoral implantation of a straight tube graft), AAA with a proximal neck (2 cm or longer), a distal neck (1.5 cm or longer), and an iliac artery diameter of 8 mm or greater (N = 19); or type II (requiring tapered aortoiliac or bifurcated grafts or access through an iliac approach), AAA that did not fit the type I criteria (N = 21). Radiographic guidance was used to pass the aortic endografts (38 Dacron and 2 PTFE) via a delivery sheath introduced through the femoral or iliac arteries into the aorta. The configuration of the aortic endografts was tubular in 26 patients, tapered aortoiliac in 11, and bifurcated in three. Successful endoluminal repair was achieved in 17 (89%) of 19 patients with type I AAA and in 15 (71%) of 21 patients with type II AAA. All failed endoluminal repairs proceeded to successful open repair, and there were no deaths during the period of hospitalization for the operation. The mean operative time and mean hospital stay were shorter in patients with type I AAA compared to patients with type II AAA. The incidence of postoperative complications was 37% in type I endoluminal repairs compared to 71% in type II endoluminal repairs. There was one cardiac death (procedure related) within 30 days, and there were three late deaths (one cardiac, one from liver failure in a type II AAA repair, and one from a ruptured esophagus in a type I repair). These preliminary results suggest that there is a better outcome in transfemoral endoluminal tube graft repair of aneurysms conforming to type I criteria compared to endoluminal repair of the more complex type II AAA.

Iliac artery evaluation with two-dimensional time-of-flight MR angiography: update

PURPOSE

To determine the accuracy of two-dimensional (2D) time-of-flight (TOF) magnetic resonance (MR) angiography, performed with state-of-the-art equipment, in the evaluation of the iliac arteries.

MATERIALS AND METHODS

The iliac arteries of 50 patients undergoing conventional arteriography for evaluation of lower-extremity ischemia or abdominal aortic aneurysm were also imaged with axial 2D TOF MR angiography. Blinded interpretations of conventional arteriograms and MR angiograms were compared. MR angiography was performed with a 1.5-T system with 2-mm contiguous axial sections, 60 degrees flip angle, 28-msec repetition time, and 7.4-msec echo time.

RESULTS

Blinded interpretations of 2D TOF MR angiograms matched those of conventional arteriograms in 26 of 50 patients (52%). For the diagnosis of obstructive iliac artery lesions, sensitivity and specificity with MR angiography were 85% and 59%, respectively. Two of three saccular iliac artery aneurysms escaped detection with MR angiography.

CONCLUSION

Iliac artery evaluation with axial 2D TOF MR angiography is not sufficiently accurate to warrant its use as a replacement for conventional arteriography in patients who lack contraindications to the latter.

Aortoiliac aneurysms: management with endovascular stent-graft placement

PURPOSE

To evaluate endovascular stent-graft placement for management of aortoiliac aneurysms.

MATERIALS AND METHODS

Balloon-expandable stents covered with polytetrafluoroethylene were placed in 11 aortoiliac lesions in nine male non-surgical candidates (mean age, 63.5 years). There were six abdominal aortic aneurysms, four iliac artery aneurysms, and one acute pseudoaneurysm from a ruptured iliac artery. Stent-grafts were dilated up to 14 mm (iliac) and 24 mm (aorta). Patients underwent follow-up computed tomography and angiography.

RESULTS

Stent-grafts were successfully placed in all 11 cases. There were two complications: a ruptured iliac artery treated with placement of an additional covered stent and a lower-extremity vessel embolization and bowel infarction resulting in death. All stent-grafts remained patent without increased aneurysmal diameter. Three leaks (27%) were detected. Two leaks were treated with placement of additional covered stents. One still is asymptomatic.

CONCLUSION

Endovascular treatment of aortoiliac aneurysms with stent-graft devices may be an alternative to surgery.

Surgical management of concurrent, coeliac and bilateral iliac artery aneurysms

A 76-year-old man was admitted with bilateral common iliac artery aneurysms found incidentally on computed tomography. Transfemoral digital subtraction arteriography demonstrated atherosclerotic plaques in the aorta with bilateral common iliac artery aneurysms and a coeliac axis aneurysm. The coeliac artery aneurysm was resected and an aortobifemoral bypass performed with reimplantation of the inferior mesenteric artery into the prosthesis. The patient was well when discharged 2 weeks after operation. The incidence, natural history and management of coeliac axis and iliac artery aneurysms are reviewed.

[Motor deficit complicating an isolated aneurysm of the internal iliac artery]

A 70-year-old man was admitted to the orthopaedic ward for severe sciatic pain and motor deficit. Diagnosis of a unique aneurysm of the right medial iliac artery and compression of the neighbouring elements was based on CT scan, echography and angiography imaging. This observation emphasizes the importance of a through physical examination. Unique aneurysm of the medial iliac artery is rarely observed. Effective treatment and satisfactory results can be obtained with simple ligature.