Reactive thrombocytosis alone does not affect the patency of microvascular anastomosis in the splenectomy rat

Vascular thrombosis is a harbinger of failure in microsurgery. However, there is still controversy regarding the correlation of the complications of thrombocytosis and thrombosis. Some evidence indicates that patients with elevated platelet counts tend to have a higher flap failure rate, and surgeons usually hesitate to operate on patients with thrombocytosis. Nevertheless, the authors have experienced successful free tissue transfer in seven patients with thrombocytosis resulting from traumatic splenectomy or multiple trauma. On the basis of clinical observation, the authors investigated whether reactive thrombocytosis contributes to the patency of a microvascular anastomosis. In a rodent splenectomy-induced thrombocytosis model (n = 40), stable reactive thrombocytosis occurred after postoperative days 5 to 10, with the peak on postoperative day 7. Femoral artery division and reanastomosis was performed in rats with or without splenectomy-induced thrombocytosis, and vascular patency was assessed. Platelet counts and platelet activation were studied in correlation to microvascular patency. Platelet activation as demonstrated by CD62P expression on platelets was not significantly different between rats with and without thrombocytosis (6.41 +/- 0.95 percent versus 4.51 +/- 0.55 percent, respectively; p = 0.089). As immature platelets were not increased (2.86 +/- 0.33 percent versus 1.99 +/- 0.32 percent, p = 0.074), it seems that the splenectomy-induced thrombocytosis is the result of redistribution of platelets instead of an increase in bone marrow production. There were no significant differences in the patency rates or perfusion units of femoral artery after arterial anastomosis between rats with and without thrombocytosis (90 percent and 95 percent, respectively; p = 0.561). In conclusion, this study demonstrates that microvascular anastomosis can be performed safely in patients with reactive thrombocytosis without platelet activation.     

End-to-end versus end-to-side microvascular anastomosis patency in experimental venous repairs

In this experimental study, venous end-to-end and end-to-side microvascular anastomoses in similar and diameter-discrepant vessels were compared. In 50 rats, end-to-end microvascular repair of the divided epigastric vein and end-to-side repair of the epigastric vein into the femoral vein showed 5-day patency rates of 75 and 88 percent, respectively. These data are not statistically different. In 20 rats, microvascular repair of end epigastric to end femoral veins (size discrepant) and end epigastric to side femoral veins showed 5-day patency rates of 50 and 85 percent, respectively. These data are statistically different (p less than 0.05). We conclude from these experimental data that end-to-side venous repairs may be useful in lowering the anastomosis thrombosis rate seen when size-discrepant veins are repaired.     

A new technique for microvascular anastomosis: external metallic circle

Vessel anastomosis is the most critical step in free tissue transfers and replantation surgery. We report on a new microvascular anastomosis technique that uses a metallic circle around the anastomotic circumference. Sutures are first passed inside the circle and tied outside and over the circle so as to stretch open the anastomotic site. By retraction of vessel ends, the circle is totally exteriorized and thus there is no contact with blood. In 48 rats, the external circle method was compared with the conventional technique for constructing end-to-end anastomosis between carotid arteries (1 to 1.2 mm) and femoral veins (1 to 1.5 mm). The external circle method proved to be superior to the conventional end-to-end technique in speed of execution for both arterial and venous anastomoses. Patency rates at the third week were significantly higher in the venous group using the metallic circle (100 percent versus 70.8 percent, p < 0.05). This new method may be applicable in clinical microvascular surgery.     

A functional model of microvascular thrombosis

A new model of microvascular thrombosis is presented, with the evaluation of single-dose heparin in the prevention of microvascular thrombosis. The technique, which involves arterial crushing and an arteriotomy with intimal abrasion, was performed on the superficial femoral artery of the rat. The model was applied to a series of 30 consecutive rat superficial femoral arteries. A 100 percent thrombosis rate was seen immediately and at 24 hours in 10 nonheparinized animals. An operator control group of 10 vessels without intimal abrasion had a patency rate of 100 percent immediately and at 24 hours. Ten vessels following single-dose heparin and intimal abrasion were all patent initially, with 7 remaining patent at 24 hours. Reproducibility of the model was documented by a second operator with similar results. Utilizing this model, single-dose heparin was effective in maintaining vessel patency.     

Use of the vascular closure staple clip applier for microvascular anastomosis in free-flap surgery

We report our initial experience using the vascular closure staple clip applier (a nonpenetrating titanium clip applied in an interrupted, everting fashion) for microvascular anastomosis in free-flap surgery. In total, 153 anastomoses were performed in 87 free flaps (174 potential anastomoses) using the vascular closure stapler between October of 1997 and June of 1999. In 66 flaps, both the arterial and venous anastomosis were performed with the clip applier, whereas in 21 flaps only the venous anastomosis was performed using the clips. A total of 146 anastomoses were performed in an end-to-end fashion, and seven were performed end-to-side. Of the 87 flaps there were 53 TRAM flaps, seven bilateral TRAM, five latissimus dorsi, four gastrocnemius, three rectus abdominis, two radial forearm fibula, and four Rubens fat-pad flaps. Seventy flaps were used for breast reconstruction, seven flaps for lower limb reconstruction, four flaps for head and neck reconstruction, and six flaps for chest wall/trunk reconstruction. There were no postoperative anastomotic complications of bleeding, thrombosis, or need for revision (100 percent patency rate), with a significantly reduced time for completion of anastomoses. The clip applier is a safe, reliable method for performing microvascular anastomoses, allowing reduced operating time and possible cost savings in free-flap surgery.     

Experience using microvascular anastomotic rings for the transplantation of 20 free flaps

A new microvascular anastomosis technique was employed with success in 1985-1986 with the result of 18 free-flap survivals and 2 failures. The rate of success in microvascular anastomoses was 90.5 percent (38 of 42). The advantages of this technique are its simplicity, convenience, and safety, and it may shorten the duration of the operation. Our experience in using vascular anastomotic rings is presented.     

Significance of venous anastomosis in fingertip replantation

Adequate venous outflow is the most important factor for successful fingertip replantation. The authors have attempted venous anastomosis in all cases of fingertip replantation to overcome postoperative congestion. In this article, the significance of venous repair for fingertip replantation is described from the authors' results of 64 complete fingertip amputations in 55 consecutive patients, which were replanted from January of 1996 to June of 2001. The overall survival rate was 86 percent. Of the 44 replantations in zone I, 37 survived, and the success rate was 84 percent. Of the 20 replantations in zone II, 18 survived, and the success rate was 90 percent. Venous anastomosis was attempted in all cases, but it was possible in 39 zone I and in all zone II replantations. For arterial repair, vein grafts were necessary in 17 of the 44 zone I and in one of the 20 zone II replantations; for venous repair, they were necessary in six zone I replantations and one zone II replantation. Postoperative vascular complications occurred in 15 replantations. There were five cases of arterial thrombosis and 10 cases of venous congestion. Venous congestion occurred in nine zone I and one zone II replantations. In five of these 10 replantations, venous anastomosis was not possible. In another five replantations, venous outflow was established at the time of surgery, but occlusion occurred subsequently. Except for the five failures resulting from arterial thrombosis, successful venous repair was possible in 49 of 59 replantations (83 percent). Despite the demand for skillful microsurgical technique and longer operation time, the authors' results using venous anastomosis in successful fingertip replantations are encouraging. By performing venous anastomosis, external bleeding can be avoided and a higher survival rate can be achieved. Venous anastomosis for fingertip replantation is a reliable and worthwhile procedure.     

Another method to prevent venous thrombosis in microsurgery: an in situ venous catheter

Free-flap failure is in the order of 4 to 10 percent. Heparin is more effective at preventing venous thrombosis than arterial thrombosis. This study was undertaken to investigate the efficacy of delivering heparin at a high dose locally but low dose systemically (heparin infusion via a catheter placed proximal to the venous anastomosis) to prevent venous thrombosis in microsurgery. A model of venous thrombosis was first established by a venous inversion graft in the rat femoral vein (this was performed in seven animals and resulted in 100 percent thrombosis). Saline and heparin were delivered proximal to the inverted vein graft to assess the effect of each in preventing venous thrombosis. Flow/patency distal to the inverted vein graft was assessed by observation under the microscope, the milk test, and rate of flow (flowmeter). Saline infused via a catheter proximal to the venous inversion graft resulted in 100 percent thrombosis in 10 animals. Heparin (100 U/ml at 2 to 3 ml/hour) infused through a catheter for 2 hours proximal to the anastomosis resulted in flow in all 10 animals during the infusion. Blood was also taken before beginning the procedure (control) and after the heparin infusion distal to the anastomosis (local partial thromboplastin time) as well as in the contralateral femoral vein (systemic). The control for all animals that received heparin was <3 minutes. The systemic partial thromboplastin time after heparin infusion was <3 minutes in seven animals, 3.3 minutes in two animals, and >7 minutes in one animal. The local partial thromboplastin time distal to the inverted vein graft was >10 minutes in nine animals and 3.7 minutes in one animal. The study also had a clinical component, in which a catheter was placed in a vein of the free flap, and heparin was infused over 5 days. This technique has been used in 83 consecutive free flaps. In three recent free flaps performed on the limbs, the local partial thromboplastin time (close to the anastomosis) was raised but the systemic time was normal. This technique offers a method in preventing venous thrombosis in microsurgery. It is simple to implement and is not associated with the systemic complications of heparin.     

A phase II trial of intraluminal irrigation with recombinant human tissue factor pathway inhibitor to prevent thrombosis in free flap surgery

A multicenter, multinational, blinded, randomized, parallel-group, phase II study was conducted to investigate the use of recombinant human tissue factor pathway inhibitor (rhTFPI; SC-59735) as an antithrombotic additive to the intraluminal irrigating solution during microvascular anastomosis in free flap reconstructive surgery. A total of 622 patients undergoing free flap reconstruction were randomly assigned to three groups. For each group, a different intraluminal irrigating solution was administered at completion of the microvascular arterial and venous anastomoses and before blood flow to the flap was reestablished: rhTFPI at a concentration of 0.05 or 0.15 mg/ml (low-dose or high-dose group, respectively) or heparin at a concentration of 100 U/ml (current-standard-of-practice group). There were no other differences in treatment among the groups. Patient characteristics, risk factors, and surgical techniques used were similar among all three groups. Flap failure was lower (2 percent) in the low-dose rhTFPI group than in the high-dose rhTFPI (6 percent) and heparin (5 percent) groups, but this difference was not statistically significant (p = 0.069). There were no significant differences in the rate of intraoperative revisions of vessel anastomoses (11 percent, 12 percent, and 13 percent) or postoperative thrombosis (8 percent, 8 percent, and 7 percent) among the low-dose rhTFPI, high-dose rhTFPI, and heparin groups, respectively. The rate of postoperative wound hematoma was significantly lower in the low-dose rhTFPI group (3 percent) than in the high-dose rhTFPI (8 percent) and heparin (9 percent) groups (p = 0.040). There were no differences in blood chemistry or coagulation values among the three study groups. Other than hematomas, there were no differences in the incidence or severity of adverse reactions among the three groups. It is concluded that use of rhTFPI as an intraluminal irrigant during free flap reconstruction is safe, well tolerated, and as efficacious as use of heparin for preventing thrombotic complications during and after the operation. Furthermore, the lower dose of rhTFPI (0.05 mg/ml) may reduce the occurrence of postoperative hematoma and help prevent flap failure.     

The role of emergent exploration in free-tissue transfer: a review of 150 consecutive cases

One-hundred and fifty consecutive free-tissue transfers were reviewed to evaluate the role of emergent exploration in flap survival. Eleven flaps exhibited signs of circulatory failure between 1 hour and 6 days postoperatively and required return to the operating room. In eight patients the preoperative diagnosis was venous thrombosis, and in three patients it was arterial thrombosis. The average time from the first abnormal examination to exploration was 1.5 hours. There were no false-positive explorations. All 11 flaps were salvaged following correction of the cause of circulatory compromise. In eight patients this was due to inflow or outflow obstruction in the recipient vessels proximal to the anastomosis, in two patients it was due to extrinsic compression of the flap from a tight wound closure, and in one patient it was due to obstruction of the recipient vein by a drain. Primary anastomotic thrombosis was not encountered as the cause of circulatory compromise in any patient. An aggressive approach to exploration was responsible for an increase in flap survival in the entire series from 90 to 98 percent. The results of this study demonstrate the efficacy of clinical monitoring, the role of early exploration, and the durability of microvascular anastomoses.     

The laser-assisted end-to-side microvascular anastomosis

A simple method of performing the laser-assisted end-to-side microvascular anastomosis was devised. This technique was tested on 150 Sprague-Dawley rats in two separate series of experiments. In the first, end-to-side anastomoses were performed on the iliac artery under the normal tension due to the elastic recoil of severed vessels. Four stay sutures were placed 90 degrees apart, and the intervals were "spot welded" with a low-wattage CO2 microsurgical laser unit. The patency rate (96 percent) was equivalent to that found in a control group utilizing the conventional all-suture method (92 percent), but there was a significantly higher aneurysm rate (44 versus 11 percent). In a second model, an arterial bypass with very low anastomotic tension was performed around an obstruction created in the carotid artery. This model resulted in turbulent flow but low anastomotic tension. Here the laser-anastomosis patency rate was 98 percent, versus 42 percent for the conventional all-suture method. The placement of fewer sutures in association with turbulent flow in this model may account for the improved patency rate. The avoidance of excessive tension at the anastomotic site reduced the incidence of aneurysms to a negligible level.     

Anastomosis of vessels of unequal diameter using an interpositional vein graft

In this study, 100 rabbits were used to assess the efficacy of five different methods of microvascular anastomosis where a vessel diameter discrepancy of 5:1 existed. The inferior vena cava of the rabbit was used as a graft in the femoral artery. In 50 percent of the rabbits the graft was reversed to assess the effects on flow. When explored between 7 and 10 days after anastomosis, an overall patency rate of 96 percent was recorded. Three grafts were not patent in the reversed group and one was not patent in the nonreversed group. There was no significant statistical difference in patency rates between any of the groups, as calculated by the Fisher's exact probability test. The tapered end-to-end and side-to-end anastomoses were found to be the most rapid and simplest methods to perform.     

Decreased thrombogenicity of vascular prostheses following gas denucleation by hydrostatic pressure

The high rate of thrombosis of 1.0-mm polytetrafluoroethylene (PTFE) grafts has limited their use in microvascular surgery. One possible reason for this is the blood-gas interface due to entrapped air in the interstices. The present study examines the effect on patency rates of elimination of this blood-gas interface by high pressurization. Comparing pressurized and nonpressurized grafts in the same animals showed a patency rate of 100 percent at 7 days for treated grafts, while the control (nonpressurized) grafts had all clotted by 1 hour. The implications for microvascular surgery as well as vascular surgery in general are discussed.     

Inhibition of microsurgical thrombosis by the platelet glycoprotein IIb/IIIa antagonist SR121566A

Despite major improvements in tools and significant refinements of techniques, microsurgical anastomosis still carries a significant risk of failure due to microvascular thrombosis. The key to improving the success of microvascular surgery may lie in the pharmacologic control of thrombus formation. Central to pathologic arterial thrombosis are platelets. Glycoprotein IIb/IIIa is a highly abundant platelet surface receptor that plays a major role in platelet aggregation by binding platelets to each other through the coagulation factor fibrinogen. To explore the ability of antithrombotic agents to prevent microvascular thrombosis, a rabbit ear artery model was used in which a standardized arterial injury results in predictable thrombus formation. This model was used to examine whether SR121566A, a specific and potent glycoprotein IIb/IIIa inhibitor, can successfully prevent microsurgical thrombosis.Using a coded, double-blind experimental design, 20 rabbits (40 arteries) were assigned to four treatment groups: (1) saline injection (n = 10), (2) acetylsalicylic acid 10 mg/kg (n = 10), (3) heparin 0.5 mg/kg bolus with subsequent intermittent boluses of 0.25 mg/kg every 30 minutes (n = 10), and (4) SR121566A 2 mg/kg bolus (n = 10). After vessel damage and clamp release, arteries were assessed for patency at 5, 30, and 120 minutes by the Acland refill test. Coagulation assays, in vivo bleeding times, and ex vivo platelet aggregation studies were also conducted. Scanning electron microscopy was used to examine mural thrombus composition.A significant, fourfold increase in vessel patency following administration of SR121566A over saline control (80 percent versus 20 percent patency, respectively, at 35 minutes after reperfusion, p < 0.01) was noted. This was correlated with marked inhibition of ex vivo platelet aggregation. This antiplatelet treatment did not prolong coagulation assays (mean international normalized ratio: saline, 0.66 +/- 0.04; SR121566A, 0.64 +/- 0.03; mean thromboplastin time: saline, 19.63 +/- 0.67; SR121566A, 17.87 +/- 3.27) and bleeding times (mean bleeding time: saline, 42 +/- 4; SR121566A, 48 +/- 6). Scanning electron microscopy demonstrated extensive platelet and fibrin deposition in control vessel thrombi. In contrast, thrombi from SR121566A-treated vessels demonstrated predominance of fibrin with few platelets when examined under scanning electron microscopy.Administration of SR121566A was associated with a significant increase in vessel patency, without deleterious effects on coagulation assays or bleeding times. The increase in vessel patency was correlated with inhibition of platelet aggregation and decreased platelet deposition, as demonstrated by scanning electron microscopy. Glycoprotein IIb/IIIa antagonists represent a new class of anti-platelet agents that may be suited for inhibiting microsurgical thrombosis. This study supports further investigation into the use of these agents in microsurgery.     

Importance of additional microvascular anastomosis in esophageal reconstruction after salvage esophagectomy

Esophageal reconstruction after salvage esophagectomy in patients who have undergone curative-intent chemoradiotherapy for esophageal cancer is associated with a significant risk of perioperative morbidity and mortality. In particular, anastomotic leakage can cause severe and potentially fatal complications, including mediastinitis and pneumonia. The authors performed esophageal reconstruction with a pedicled right colon graft after salvage esophagectomy in eight patients. To decrease the rate of anastomotic leakage, the authors performed an additional microvascular anastomosis at the distal end of the graft. The distal stumps of the ileocolic artery and vein were anastomosed to the cervical vessels. After surgery, aspiration pneumonia and localized wound infection were observed in two patients each, but slight anastomotic leakage was observed in only one patient. Postoperative swallowing function was satisfactory in all patients. Although the incidence of anastomotic leakage is reportedly high, the authors observed anastomotic leakage in only one of eight patients. The authors believe that additional microvascular anastomosis helps prevent anastomotic leakage, especially in patients who have undergone salvage esophagectomy after curative chemoradiotherapy.     

Thrombosis of microvascular anastomoses in traumatized vessels: fibrin versus platelets

Thrombosis is the end result of two closely interrelated processes: the coagulation cascade and the platelet aggregation process. To determine their relative contribution, we used pharmacologic agents that selectively block each process. The specific effect of each pharmacologic agent on either fibrin deposition or platelet activity was confirmed morphologically by scanning electron microscopy and was substantiated with ADP-induced platelet aggregation and blood clotting time determinations. Forty-two rats had both femoral arteries subjected to a standardized crush-avulsion injury. A total of 84 femoral microvascular anastomoses were subsequently performed. None of the 24 control anastomoses treated with saline remained patent, whereas 6 of 24 of the anastomoses treated with dazmagrel (a selective thromboxane synthetase and platelet aggregation inhibitor), 2.5 mg/kg IV, remained patent and 18 of 24 of those treated with a single dose of heparin, 200 U/kg IV, remained patent. All 12 anastomoses treated with both drugs remained patent but developed a 33 percent hematoma rate. We conclude that in this microvascular model, fibrin mesh deposition is a more significant factor than platelet aggregation in the pathogenesis of occlusional thrombosis within traumatized arteries. Its temporary inhibition with a single dose of heparin yielded a 75 percent improvement in patency rate.     

Alternative venous outflow vessels in microvascular breast reconstruction

The lack of adequate recipient vessels often complicates microvascular breast reconstruction in patients who have previously undergone mastectomy and irradiation. In addition, significant size mismatch, particularly in the outflow veins, is an important contributor to vessel thrombosis and flap failure. The purpose of this study was to review the authors' experience with alternative venous outflow vessels for microvascular breast reconstruction. In a retrospective analysis of 1278 microvascular breast reconstructions performed over a 10-year period, the authors identified all patients in whom the external jugular or cephalic veins were used as the outflow vessels. Patient demographics, flap choice, the reasons for the use of alternative venous drainage vessels, and the incidence of microsurgical complications were analyzed. The external jugular was used in 23 flaps performed in procedures with 22 patients. The superior gluteal and transverse rectus abdominis musculocutaneous (TRAM) flaps were used in the majority of the cases in which the external jugular vein was used (72 percent gluteal, 20 percent TRAM flap). The need for alternative venous outflow vessels was usually due to a significant vessel size mismatch between the superior gluteal and internal mammary veins (74 percent). For three of the external jugular vein flaps (13 percent), the vein was used for salvage after the primary draining vein thrombosed, and two of three flaps in these cases were eventually salvaged. In three patients, the external jugular vein thrombosed, resulting in two flap losses, while the third was salvaged using the cephalic vein. A total of two flaps were lost in the external jugular vein group. The cephalic vein was used in 11 flaps (TRAM, 64.3 percent; superior gluteal, 35.7 percent) performed in 11 patients. In five patients (54.5 percent), the cephalic vein was used to salvage a flap after the primary draining vein thrombosed; the procedure was successful in four cases. In three patients, the cephalic vein thrombosed, resulting in two flap losses. One patient suffered a thrombosis after the cephalic vein was used to salvage a flap in which the external jugular vein was initially used, leading to flap loss, while a second patient experienced cephalic vein thrombosis on postoperative day 7 while carrying a heavy package. There was only one minor complication attributable to the harvest of the external jugular or cephalic vein (small neck hematoma that was aspirated), and the resultant scars were excellent. The external jugular and cephalic veins are important ancillary veins available for microvascular breast reconstruction. The dissection of these vessels is straightforward, and their use is well tolerated and highly successful.     

The thoracodorsal artery perforator flap: clinical experience and anatomic study with emphasis on harvest techniques

The thoracodorsal artery perforator flap is a relatively new flap that has yet to find its niche in reconstructive surgery. At the authors' institution it has been used for limb salvage, head and neck reconstruction, and trunk reconstruction in cases related to trauma, burns, and malignancy. The authors have found the flap to be advantageous for cranial base reconstruction and for resurfacing the face and oral cavity. The flap has been used successfully for reconstruction of traumatic upper and lower extremity defects, and it can be used as a pedicled flap or as a free tissue transfer. The perforating branches of the thoracodorsal artery offer a robust blood supply to a skin-soft-tissue paddle of 10 to 12 cm x 25 cm, overlying the latissimus dorsi muscle. The average pedicle length is 20 cm (range, 16 to 23 cm), which allows for a safe anastomosis outside the zone of injury in traumatized extremities; the flap can be made sensate by neurorrhaphy with sensory branches of the intercostal nerves. Vascularized bone can be transferred with this flap by taking advantage of the inherent vascular anatomy of the subscapular artery. A total of 30 pedicled and free flap transfers were performed at the authors' institution with an overall complication rate of 23 percent and an overall flap survival rate of 97 percent. Major complications, such as vascular thrombosis, return to the operating room, fistula formation, recurrence of tumor, and flap loss, occurred in 17 percent of the patients. Despite these drawbacks, the authors have found the thoracodorsal artery perforator flap to be a safe and extremely versatile flap that offers significant advantages in acute and delayed reconstruction cases.     

Application of the cross-bridge microvascular anastomosis when no recipient vessels are available for anastomosis: 85 cases

The purpose of this article is to introduce the results of free tissue transfers using the technique of the cross-bridge microvascular anastomosis when the recipient lacks suitable vessels for anastomosis. Between May of 1982 and June of 2002, a series of 85 patients underwent this procedure. The transferred tissues were the free latissimus dorsi myocutaneous flap, the free vascularized fibula, the free fibular osteocutaneous flap, and the free iliac osteocutaneous flap, alone or in combination. The donor vessels were the anterior tibial artery and great saphenous vein, the posterior tibial artery and its venae comitantes, and the radial artery and cephalic vein. Good results were achieved. The success rate reached 95.29 percent. The authors believe this procedure can be performed in the event of serious tissue defect where the vessels are unsuitable for anastomosis.     

Further studies on prevalence of hydatidosis in slaughtered animals from North Jordan

Examination of 471 sheep, 118 goats, 157 cattle and 56 camels slaughtered in abattoirs in North Jordan was carried out during March-May 1984. Drought conditions that prevailed during the preceding winter led to slaughtering old female sheep (greater than or equal to 4 years) due to scarcity of food, which allowed us to analyse the prevalence of hydatidosis in various age groups of sheep. An overall infection rate of 27.8, 1.7, 5.8 and 10.7 percent was found in sheep, goats, cattle and camels, respectively. The infection rate was as low as 1.5 percent in male and 1.9 percent in female sheep under 2 years of age. However, the rate of hydatid infection increased with age and reached as high as 63.7 percent in ewes 4 years of age and older. The percentage of animals with fertile cysts was also highest in sheep (68.7 percent of infected animals) and increased with age reaching 100 percent in ewes which were 10 years of age or older. Analysis of all cysts recovered from the livers and lungs of infected ewes from various age groups revealed a sharp increase in the mean total number of cysts in age groups over 8 years of age. The fertility rate of the cysts in the liver was significantly greater in ewes 6 years old or more (64.8--78.6 percent) than in younger age groups (8.7-46.2 percent). In the lung, the fertility rate increased progressively with age reaching as high as 97.9 percent in ewes 10 years old or more. These findings of high infection and fertility rates of hydatid disease in sheep, particularly of older age groups, prompt plans for further epidemiological studies and control programmes.