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Objective: Skin-sparing mastectomy (SSM) is a novel operation that offers better aesthetic outcomes than conventional mastectomy (total mastectomy (TM) or modified radical mastectomy (MRM)). For oncologic safety, it is widely accepted that SSM with immediate breast reconstruction (IBR) offers no statistically significant difference in terms of locoregional recurrence and distant metastasis when performed in early stage breast cancer. The present study aimed to study the oncological safety of SSM with IBR in Tis--T2 breast cancer patients in an Asian population. Materials and Methods: The data of breast cancer patients who underwent SSM or TM both with IBR from January 2005 to December 2013 were retrospectively reviewed. The inclusion criteria were a pathological in situ or invasive breast cancer sized <5 cm and a follow-up duration of at least 24 months. A comparison of locoregional recurrences, distant metastasis, 5-year disease-free, and overall survival rates between the two groups was performed and the results analyzed. Results: The authors identified 291 patients (292 operations). The median follow-up times were 81 months in the TM group (n = 148) and 59 months in the SSM group (n = 144). There was no statistically significant difference in tumor characteristics or AJCC staging, except for a higher positive hormonal receptor status in the SSM group. There was no difference in the rates of locoregional recurrences, distant metastasis, 5-year disease-free, and overall survival between the two groups. Conclusion: SSM is a good option for mastectomy because the preserved skin provides a better aesthetic outcome and there was no difference in recurrence rates between TM and SSM with IBR in breast cancer. Also, the 5-year disease-free and overall survival rates were comparable between both groups. SSM with IBR should therefore be considered an oncologically safe operation in breast cancers less than 5 cm in size. [ABSTRACT FROM AUTHOR]

Objective: To investigate the outcomes of retrograde intrarenal surgery (RIRS) for large renal calculi, and to identify factors that influence the stone-free rate after RIRS for renal stone burden greater than 2 centimeters. Materials and Methods: This retrospective chart review included patients who underwent RIRS for renal calculi greater than 2 centimeters in size during January 2015 to December 2016 at Siriraj Hospital Thailand's largest national tertiary referral center. Data were collected and compared between those having and not having residual stones greater than 2 cm in diameter. Results: The present study included 100 eligible cases. The most common site was at lower calyces (42%). The mean stone burden size was 31.43 mm (range: 20 to 140). The average operative time was 62 minutes (range: 20 to 150), and the mean hospital length of stay was 2.7 days (range: 1 to 22). The most common stone composition was calcium oxalate monohydrate (37%), followed by calcium phosphate (23%). The success rate was 84% and 94% after the 1st session and 2nd session of RIRS, respectively. The factors that were found to predict residual stone after RIRS were stone burden greater than 35 mm in size (odds ratio [OR]: 5.86, 95% confidence interval [CI]: 1.77 to 19.57; p = 0.004) and lower pole location (OR: 1.97, 95% CI: 1.039 to 3.742; p = 0.038). Sepsis was found in 6 patients, all of whom were successfully treated with intravenous antibiotic, except for one mortality in an immunocompromised patient. Conclusion: RIRS is a promising treatment option for renal calculi with large stone burden. Large kidney stones (>2 cm) can be treated with high success rate and low morbidity. The most significant predictors of residual calculi are stone burden more than 35 millimeters in size and lower pole location. [ABSTRACT FROM AUTHOR]

Summary: Optimal reconstruction of weight-bearing plantar foot defects is challenging due to the need for relatively thin coverage with simultaneous durability. The medial plantar flap provides an excellent tissue match but is not always available or appropriate (Figure 1, 2). Microsurgical free flap reconstruction provides many options for coverage. However, few skin flaps are thin enough to contour appropriately but still provide thick dermis for durable weight-bearing; particularly in patients with an average or obese body habitus.1 Lately, the suprascarpal ("superthin") plane of elevation has been increasingly used to provide tailored coverage with appropriate thickness matching to the surrounding tissues.2,3 Even thinner "ultrathin flaps" are raised within the subcutaneous fat superficial to the Scarpa's layer.4 The superficial circumflex iliac artery (SCIP) and anterolateral thigh (ALT) perforator flaps are commonly suprascarpally elevated,5,6 and the ultrathin SIEA flap has been recently described.7 The scapular and parascapular flaps have many ideal characteristics, including thick skin,8 minimal donor site morbidity, simple pedicle dissection, and a lengthy robust pedicle. Obese subcutaneous tissue typically precludes use, and para-/scapular flaps may be overlooked for ultrathin elevation. We describe the utility of ultrathin parascapular flaps (UPF) in weight-bearing plantar foot defects., (Copyright © 2024 by the American Society of Plastic Surgeons.)

End-to-side (ETS) microsurgical anastomosis is a powerful technique in microsurgery. It can overcome vessel's diameter discrepancy and preserve the distal blood flow. Optimal angle of the ETS anastomosis has been debated and studied, and is currently limited to animal models. Computational model using Finite Element Analysis (FEA) was used to simulate the models with 45 (model 45 ), 90 (model 90 ), and 135 (model 135 ) ETS anastomosis angles. Flow dynamics including flow velocity and wall shear rate were studied and compared. Maximum flow velocity ranged from the highest to the lowest in model 135 , model 90 , and model 45 , respectively. The velocity in model135 showed fluctuation flow. The maximum wall shear rate and distribution were highest in model 45 and lowest in model 90 . ETS anastomosis angle of 90 degrees provided the most favourable flow dynamics to prevent shear related thrombosis in comparison to ETS anastomosis at 45 and 135 degrees., (© 2024. The Author(s).)

Background: In breast reconstruction, arterial coupling has been reported to be more favorable in the thoracodorsal artery (TDA) than the internal mammary artery (IMA). This technique may help overcome anastomosis in a small, deep space. Understanding the arteries' mechanical properties is crucial for breast reconstruction's safety and success., Methods: Abdominal-based free flap breast reconstructions performed by a single surgeon between 2020 and 2022 were retrospectively analyzed. The patients were classified by microanastomosis technique (handsewn and coupler device) to compare the rate of vascular revision. Histomorphometric analysis of arterial coupling in TDA and IMA was performed in 10 fresh cadavers for comparing wall thickness and composition, including densities of elastic fiber, smooth muscle, and collagen., Results: A total of 309 patients (339 reconstructed breasts) were included. There were 29 patients in the TDA handsewn group (A), 38 patients in the TDA coupler group (B), and 242 patients in the IMA handsewn group (C). The rates of arterial revision in groups A, B, and C were 0.00% (95%CI: 0.00%-11.03%), 2.5% (95%CI: 0.44%-12.88%), and 1.49% (95%CI: 0.58%-3.77%), respectively, with no statistically significant differences (p-value = .694). Histologically, the thickness of the tunica media and adventitia between IMA and TDA showed no significant difference. The density of elastic fiber was significantly higher in IMA (16.70%) than in TDA (0.79%) (p-value <.001)., Conclusion: The histologic characteristics of TDA are more favorable for arterial coupling than those of IMA. Arterial coupling is a safe option in situations where TDA anastomosis must be performed through a narrow and deep incision., (© 2024 Wiley Periodicals LLC.)

Background: Parry-Romberg syndrome (PRS) is a rare condition characterized by a progressive shrinkage and degeneration of the tissues beneath the skin, usually on one side of the face. Managing this disease presents numerous challenges due to its heterogeneity and unpredictable outcomes. The existing literature is primarily composed of case reports and series, leading to a lack of comprehensive guidelines on surgical intervention for the various manifestations of PRS. We propose an approach to address these challenges and optimize surgical outcomes., Methods: We conducted a retrospective review of all patients who underwent surgical correction for PRS between 2012 and 2022. Surgical interventions were determined based on the location and severity of the facial defect. The revision procedures were tailored to each patient until they were satisfied with the results., Results: Eleven patients underwent surgical correction, with an average of 3.2 procedures per patient. Fat grafting or dermal fat grafting was sufficiently effective for mild deficits in all areas and for upper-third deficits regardless of severity. For moderate to severe defects in the mid and lower face, a combination of buried free flaps and fat grafting yielded satisfactory results. Upon final revision, all patients rated their results as satisfactory or excellent., Conclusions: We propose an approach to surgical management that takes into account the specific deficits of each patient. Our approach has proven to yield aesthetically pleasing and reliable results, aligning with findings in the existing literature. This method could provide a foundation for standardized guidelines and improve the prognosis for individuals with PRS., Competing Interests: The authors have no financial interest to declare in relation to the content of this article., (Copyright © 2024 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The American Society of Plastic Surgeons.)

Background: This study describes the utilization of the radial forearm free flap (RFFF) for the restoration of severe soft tissue deficiency involving the upper and lower eyelids in three patients., Methods: This study is a retrospective review of the senior authors' clinical records for patients who presented with periorbital defect and underwent reconstruction with RFFF between 2018 and 2022., Results: As a part of a comprehensive reconstructive surgery, we used the RFFF to deliver an ample amount of well-vascularized soft tissue. The flap's vessels were anastomosed to the ipsilateral facial vessels in all cases. Patients showed significant functional improvement, with complete eyelid closure achieved. No immediate postoperative complications were noted., Conclusions: RFFF demonstrated optimal outcomes in upper eyelid reconstruction., Competing Interests: The authors have no financial interest to declare in relation to the content of this article., (Copyright © 2024 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The American Society of Plastic Surgeons.)

Background:  Superficial inferior epigastric artery (SIEA) flap offers a significant advantage of lower donor site morbidity over other abdominal-based flaps for breast reconstruction. However, the inconsistent anatomy and territory across the midline remains a major issue. This study aimed to investigate the SIEA and determine its pattern and territory across the midline., Methods:  Twenty cadavers were studied. Ipsilateral dye was injected to the dominant SIEA. Dissection was performed to evaluate the SIEA origin, artery and vein pattern, vessel diameter, and dye diffusion territory., Results:  Overall, three SIEA patterns were identified: bilateral presence (45%), ipsilateral presence (30%), and bilateral absence (25%). The territory depended on the vessel course and dominant SIEA diameter, not on its common origin from the femoral artery, at the pubic tubercle level. Regarding the midline territory (pubic tubercle level to umbilicus), SIEA (type 1a) with a diameter of ≥1.4 mm on either side supplied at least half the distance, whereas SIEA with a diameter of <1 mm was limited to the suprapubic area., Conclusion:  Designing a SIEA flap island across the midline is feasible when contralateral SIEA is present to augment the contralateral territory (e.g., type 1a SIEA) or in SIEA with a common/superficial external pudendal artery origin. Preoperative imaging studies are important for confirming the SIEA system. When the diameter at the origin of the SIEA flap is larger than 1.4 mm, the blood supply to the ipsilateral and contralateral sides is sufficient to enable safe flap elevation., Competing Interests: None declared., (Thieme. All rights reserved.)

Keloid is a burdensome condition that negatively affects patient's quality of life. It is influenced by a spectrum of risk factors, including tension. We propose an approach to address the tension-free closure and optimize surgical outcomes in neck keloid. A retrospective review of neck keloid patients who underwent surgical treatment between 2014 and 2022 was performed. Five patients underwent surgical interventions. Two patients had sufficient and three had insufficient tissue redundancy. The former underwent keloid excision with tension-free closure. The latter underwent keloid excision with full thickness skin graft for tension-free closure. One patient required re-excision with free flap coverage. All patients received postoperative low dose radiation. All patients were satisfied with the results and there were no signs of keloid recurrence during the follow-up period. Tension during closure following keloid excision is a modifiable risk factor. An appropriate algorithm providing tension-free closure can minimize the recurrence., Competing Interests: The authors have no conflicts of interest or products that are used in this manuscript., (Published by Oxford University Press and JSCR Publishing Ltd. © The Author(s) 2024.)

Purpose: This study aims to compare two surgical techniques, the standard Vein-to-Artery and the newer Artery-to-Vein (Radial Artery Deviation And Reimplantation; RADAR), for enhancing the success of Arterio-Venous Fistula maturation in end-stage renal disease patients. The impact of diseases like anemia, diabetes, hypertension, and chronic kidney disease were considered. The goals are to advance Arterio-Venous Fistula (AVF) surgery, improve patient outcomes, and contribute to evidence-based surgical guidelines., Methods: Fluid-structure interaction modeling was employed to investigate how hemodynamic and mechanical stresses impact arteriovenous fistula maturation, with a particular focus on the role of wall shear stress in determining maturation outcomes. The critical threshold for vessel injury was identified as wall shear stress values exceeding 35 N/m2, while stenosis formation was projected to occur at levels below 1 N/m2. This work introduced a novel approach by considering disease-related factors, including blood viscosity (anemia), and vessel elasticity (diabetes, hypertension, and chronic kidney diseases), which directly influence hemodynamics and the generation of wall shear stress. Furthermore, the model was designed to incorporate varying thicknesses and elasticities for both the vein and artery, accurately representing authentic vascular anatomy., Results: The RADAR technique has demonstrated superior performance compared to the standard technique by providing appropriate wall shear stress in critical regions and minimizing the risk of wall damage. Its use of a thicker vessel also reduces the risk of vessel injury, making it particularly effective for patients with Chronic Kidney Disease (CKD), hypertension, anemia, and diabetes, ensuring optimal blood flow and fewer complications. However, there are minor concerns about stenosis formation in hypertension and anemia cases, which could be mitigated by adjusting the anastomosis angle to be lower than 30°., Conclusion: Diabetes and hypertension have significant physiological effects that increase the risks associated with arteriovenous fistula maturation. The anemic condition resulting from CKD may help reduce vessel injury but raises concerns about potential stenosis formation. Despite these co-morbidities, the RADAR technique has demonstrated its ability to induce more favorable hemodynamic changes, promoting arteriovenous fistula maturation., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Wongchadakul et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Purpose: This study contributes to the multidisciplinary understanding of septal L-strut reshaping and introduces innovative surgical design concepts based on engineering principles of static equilibrium. The objective is to enhance structural strength and stability, ultimately leading to improved surgical outcomes., Method: Finite element analysis is employed to model the three-dimensional septal cartilage in septoplasty. A significant contribution of this work is the introduction of an innovative redesigns for the septal L-strut structure. These redesigns represent the first-ever attempt to incorporate the center of gravity theory into the modeling of the septal L-strut., Results: Our findings emphasize the significance of attaining a lower center of gravity in the design of the septal L-strut, as it contributes to optimal core strength and stability. To achieve this, we recommend widening the caudal septum and shaping the interior fillet corner to its maximum size, taking into account its specific shape. Notably, the utilization of a standard 20x20 mm septal L-strut, the C-shaped technique, and the septal support graft technique provide superior strength due to enhanced basement support., Conclusion: To enhance surgical outcomes in septal L-strut procedures, design modifications are proposed to improve strength and stability, resulting in optimized performance. Recommendations include widening the caudal septum and incorporating fillet shapes in the geometry to lower the center of gravity., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Wongchadakul et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: The ultrasound-guided proximal intercostal block (PICB) is performed at the proximal intercostal space (ICS) between the internal intercostal membrane (IIM) and the endothoracic fascia/parietal pleura (EFPP) complex. Injectate spread may follow several routes and allow for multilevel trunk analgesia. The goal of this study was to examine the anatomical spread of large-volume PICB injections and its relevance to breast surgery analgesia., Methods: Fifteen two-level PICBs were performed in ten soft-embalmed cadavers. Radiographic contrast mixed with methylene blue was injected at the 2nd(15 ml) and 4th(25 ml) ICS, respectively. Fluoroscopy and dissection were performed to examine the injectate spread. Additionally, the medical records of 12 patients who had PICB for breast surgery were reviewed for documented dermatomal levels of clinical hypoesthesia. The records of twelve matched patients who had the same operations without PICB were reviewed to compare analgesia and opioid consumption., Results: Median contrast/dye spread was 4 (2-8) and 3 (2-5) vertebral segments by fluoroscopy and dissection respectively. Dissection revealed injectate spread to the adjacent paravertebral space, T3 (60%) and T5 (27%), and cranio-caudal spread along the endothoracic fascia (80%). Clinically, the median documented area of hypoesthesia was 5 (4-7) dermatomes with 100 and 92% of the injections covering adjacent T3 and T5 dermatomes, respectively. The patients with PICB had significantly lower perioperative opioid consumption and trend towards lower pain scores., Conclusions: In this anatomical study, PICB at the 2nd and 4th ICS produced lateral spread along the corresponding intercostal space, medial spread to the adjacent paravertebral/epidural space and cranio-caudal spread along the endothoracic fascial plane. Clinically, combined PICBs at the same levels resulted in consistent segmental chest wall analgesia and reduction in perioperative opioid consumption after breast surgery. The incomplete overlap between paravertebral spread in the anatomical study and area of hypoesthesia in our clinical findings, suggests that additional non-paravertebral routes of injectate distribution, such as the endothoracic fascial plane, may play important clinical role in the multi-level coverage provided by this block technique.

Background: Microsurgical anastomosis of the dorsal artery of the penis either with or without anastomosis of the cavernosal artery is the preferred technique for penile replantation. However, postoperative penile skin necrosis is commonly reported with this technique. This study aimed to characterize the anatomy of the vascular supply of the penis pertinent to penile replantation surgery and to report a successful case of penile replantation without postoperative necrosis using anastomosis of the inferior external pudendal artery., Methods: The authors dissected 15 penises of fresh cadavers under acrylic dye injection by means of the inferior external pudendal and dorsal arteries of the penis to identify vascular anastomoses between arteries supplying the penis and to measure other parameters of the arteries., Results: Mean diameters at the base of the penis of the inferior external pudendal, dorsal, and cavernosal arteries were 0.94, 1.43, and 0.80 mm, respectively. Penile skin is mainly supplied by the inferior external pudendal artery under three patterns with anastomoses across the midline. Preputial skin receives additional blood supply from perforators of the dorsal artery without visible anastomosis between the perforators and the inferior external pudendal artery. Deep structures receive blood supply from the dorsal, cavernosal, and urethral arteries, with visible anastomoses between the arteries. In a patient with amputated penis, the inferior external pudendal artery diameter was 0.7 mm, which was sufficient for microsurgical anastomosis. No postoperative necrosis developed, and patency of the inferior external pudendal artery was confirmed with duplex ultrasound., Conclusion: The diameter of the inferior external pudendal artery at the base and midshaft of the penis is sufficiently large for microsurgical anastomosis, and additional vascular anastomosis of at least one inferior external pudendal artery may help to prevent postoperative penile skin necrosis., Clinical Question/level of Evidence: Therapeutic, V.

Purpose: The dose distributions obtained from three imaging approaches for target delineation in cervical cancer using high-dose-rate (HDR) brachytherapy were investigated., Material and Methods: Ten cervical cancer patients receiving four fractions of HDR brachytherapy were enrolled. Based on different imaging approaches, three brachytherapy plans were developed for each patient: with the high-risk clinical target volume (HRCTV) delineated on magnetic resonance (MRI) images for every fraction (approach A; MRI-only); on MRI for the first fraction and computed tomography (CT) images for the subsequent fractions (approach B; MRI 1st /CT); and on CT images for all fractions (approach C; CT-only). The volume, height, width at point A, width at maximum level, and dosimetric parameters (D 100 , D 98 , D 95 , and D 90 of the HRCTV; and D 0.1cc , D 1cc , and D 2cc of all organs at risk, or organ at risk - OAR: bladder, rectum, sigmoid colon, and bowel) provided by each approach were compared., Results: The mean HRCTV volume, width, and height obtained from approach C (CT-only) were overestimated compared to those from approaches A (MRI-only) and B (MRI 1st /CT). The doses to the HRCTV for approaches A and B were similar. However, the HRCTV doses for approach C were significantly lower than those for approaches A and B for all parameters (D 95 -D 100 ). As to the OAR, the three approaches showed no differences., Conclusions: A combination of MRI and CT is a safe alternative approach for cervical cancer HDR brachytherapy. The technique provides comparable dosimetric outcomes to MRI-based planning, while being more cost-effective., Competing Interests: Authors report no conflict of interest.

Background: Medial plantar artery perforator (MPAP) flap was proposed as proper option for finger pulp reconstruction. To provide the previously unavailable vessel information required for this small flap design, this study aimed to gather all necessary anatomy of MPA, MPAP, and their territories of blood supply to apply in clinical MPAP flap reconstruction minimizing perforator injury., Methods: Dissection of 30 Thai cadaveric feet for visualizing superficial branch of MPA and its perforators (MPAP) using acrylic dye cannulation were performed. Diameter, length, number of branches, course, distributing areas of these vessels, and also their areas of blood supply were recorded in relation to specified landmarks, eg, C-MTH line; medial calcaneal tuberosity to plantar side of the first metatarsal head and S point; emerging point of superficial branch of MPA from deep fasciae into subcutaneous layer., Results: Average diameter of MPA at its origin and total length are 1.63 ± 0.3 and 52.8 ± 16.1 mm, respectively. It provides 1-3 perforators, with an average size and length of 0.36 ± 0.11 and 23.2 ± 5.47 mm, respectively. Its distribution is mostly in the posteromedial quadrant within 50 and 30 mm from the midpoint of C-MTH line and the S point, respectively. The estimated perforator flap area is 2.5 cm × 1.5 cm and 4.5 cm × 2.5 cm for single and double perforators, respectively., Conclusions: MPAP flap was proved as another ideal option for finger pulp reconstruction. Its limitation is small size of perforators but this can be overcome by using MPA for microsurgical anastomosis instead., (© 2018 Wiley Periodicals, Inc.)

Purpose: Titanium ring cap applicator (VariSource) was applied in treating cervical cancer patients by using image-guided brachytherapy (IGBT). However, its sizes appeared to be relatively large for most of our patients. Thus, we have developed a specific applicator "Siriraj Ring Cap," which is slightly smaller and more suitable for our patients. This study was to evaluate effectiveness of this equipment., Methods and Materials: Locally advanced cervical cancer patients were treated with external beam radiation therapy with or without concomitant chemotherapy. Siriraj Ring Cap was applied in all of the patients for at least one fraction. Dosimetric analysis was performed in each fraction of IGBT. Clinical outcomes of these patients were evaluated., Results: Twenty-nine patients with 117 dosimetric planning were evaluated between January and December of 2014. Siriraj Ring Cap was fit to all patients in this study. By using this applicator, radiation doses to the targets (D 90 high-risk clinical target volume and D 90 intermediate-risk clinical target volume) were higher in each fraction. There were no statistically differences of radiation doses to the bladder, rectum, sigmoid colon, and small bowel. Within 2-year followup, 3 patients (10.3%) developed locoregional recurrence. Two-year disease-free survival and overall survival were 75.9% and 89.7%, respectively. According to RTOG/EORTC complication criteria, Grade 1, 2, and 3 gastrointestinal complications were developed in 2 (6.9%), 4 (13.8%), and 1 (3.4%) patients, respectively. For genitourinary complications, 3 patients (10.3%) and 1 patient (3.4%) had Grades 1 and 2, respectively., Conclusions: Siriraj Ring Cap is feasible for IGBT in cervical cancer patients with narrow vagina. Dosimetry and clinical outcomes were satisfactory by using our specific applicator., (Copyright © 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

A staged auricular reconstruction in microtia patients was developed by using superficial mastoid fascia (as part of extrinsic postauricular fascia) to cover the cartilagenous framework due to its highly vascularized nature. Three branches of external carotid artery (superficial temporal artery, posterior auricular artery and occipital artery) were found to supply this fascia, this study was therefore aimed to investigate the dimension of blood supply from each vessel and also to demonstrate the existence of anastomoses among these arteries. Thirty-eight pinnas and postauricular fascias from Thai fresh adult cadavers were included to document the anastomoses by showing both perfused dye connection (10 dissections) and visible anastomotic branches (8 dissections) among them. Distribution of each vessel trunk and its branches were demonstrated using superimposed illustration in the other 20 dissections with dye injection into each artery to designate 3 zones of anastomotic area between each arterial pair. Maximal size of viable postauricular fascial flap for staged reconstruction according to this vascular study was thus estimated to be at least 5 cm above and 3 cm below the Frankfurt horizontal plane and about 6 cm posterior to external acoustic meatus owing to the course of posterior auricular artery and its anastomoses. In addition, greater size of flap with dual blood supply from both superficial temporal and posterior auricular arteries can be raised by harvesting beyond 5 cm above external acoustic meatus.