Staging arteriovenous fistula loops for lengthening of free-flap pedicles

The authors investigated the optimal period of maturation following the creation of arteriovenous (AV) loops using polyterafluoroethylene (PTFE) in a white rat model, which were subsequently used to support free-tissue transfer The AV loops in Group 1 (n = 17) were allowed to mature for 3 days prior to creation of the flap, while those from Group 2 (n = 14) were allowed to mature for 5 days. Results were compared to those from a previous study in which the authors reported an 80 percent initial patency rate (n = 30) and a 67 percent viability rate, based on 12 patent loops after 7 days. In the present study, patency rates were 59 percent for the 3-day group and 79 percent for the 5-day group; viability rates were 50 and 64 percent, respectively. Considering both patent and nonpatent loops, the overall viability rates were 29 and 50 percent respectively. Maturation periods longer than 3 days for AV loops constructed from PTFE micrografts were determined to be preferable for subsequent free-tissue transfer.

Locally administered vascular endothelial growth factor cDNA increases survival of ischemic experimental skin flaps

Microvascular surgery has emerged as an attractive area for recent advances in the field of gene therapy. The present study investigated the survival of ischemic, experimental skin flaps after treatment with the gene encoding vascular endothelial growth factor (VEGF). In 30 Sprague-Dawley rats, anterior abdominal skin flaps supplied by the epigastric artery and vein were created. Ten animals were treated with a mixture of liposomes and the cDNA encoding the 121-amino acid isoform of VEGF. Another 10 animals were treated with control plasmid DNA and liposome transfection medium; a third group of 10 animals was given physiologic saline. Each solution was injected directly into the femoral artery distal to the origin of the epigastric pedicle supplying the flap. Four days after injection, the pedicle was ligated and blood flow in the flap was approximated using dye fluorescence. Seven days later, the amount of viable tissue within the flap was measured by planimetry. After the animals were killed, specimens from both the operated and nonoperated sides of the abdomen were harvested for immunohistologic evidence of VEGF protein expression. Average dye fluorescence indices of the three groups (VEGF cDNA, control plasmid, and saline) 2 hours after pedicle ligation were 35.9, 23.9, and 53.9 percent, respectively (p < 0.05). Compared with the two control groups, flaps receiving VEGF cDNA had significantly greater tissue viability at the end of 7 days: 93.9 versus 28.1 percent for the control plasmid DNA group and 31.9 percent for the saline group (p < 0.05). Immunohistochemical staining documented increased deposition of VEGF protein in flaps that were infused with the VEGF cDNA versus saline alone (p < 0.05). The results indicated that the survival of ischemic tissues can be enhanced by administration of a cDNA encoding VEGF, a protein known to be important in the process of angiogenesis and wound healing.

Lymphatic mapping in the management of melanoma in children

Lymphatic mapping allows the surgeon to identify and remove the first draining (sentinel) lymph node from a primary melanoma with minimal morbidity. The procedure facilitates accurate staging and identification of patients in need of additional therapy. We used lymphatic mapping and sentinel lymph node biopsy in two children with melanoma. Both patients had evidence of metastatic melanoma in their sentinel lymph nodes and underwent regional lymphadenectomy. Malignant melanoma and atypical pigmented lesions in children remain diagnostically challenging for the pathologist and clinician. Misdiagnoses occur, and the correct interpretation of a melanocytic tumor is too often made only after recurrence or metastasis has occurred. The use of lymphatic mapping facilitates accurate staging and identifies children in whom additional therapy may be indicated. In addition, it can assist in the assessment of the biologic potential of a difficult lesion.

The advanced-stage therapy group

Many authors describe a stage of maturity in the development of groups, but each highlights a different dimension. This article describes the characteristics of the advanced stage and the main axes along which it develops (internalization and containment, symbolization, self and self-other development, differentiation and individuation). It also offers a conceptual explanation for these developments and attempts to identify the conditions necessary for the emergence of this stage of maturity. An understanding of this stage and the conditions required for its development can be used by the group leader as a compass to help him or her navigate the group toward this objective.

Effect of time on the viability of ischemic skin flaps treated with vascular endothelial growth factor (VEGF) cDNA

This study examined the efficacy of gene therapy on wound healing. The authors investigated whether delivery of the gene encoding a particular cytokine, known to be important in angiogenesis, could affect ischemic skin flaps. Anterior abdominal skin flaps, based solely on the epigastric artery and vein, were created in the Sprague-Dawley rat model. At the time of elevation, the arterial pedicle supplying each flap was infused either with the gene for vascular endothelial growth factor (VEGF) or physiologic saline alone. The flaps were resutured into place and observed for a period of either 4 or 3 days, at which time the pedicle was ligated. Twenty minutes following ligation, blood flow in the flaps was measured by dye fluorescence. Tissue viability of the flaps was subsequently measured by planimetry after a period of 7 days. Flaps that received the VEGF gene and were ligated at 4 days had an average dye fluorescence index (DFI) of 31.1 following ligation, and 93.9 percent viable tissue after 7 days. Flaps that received saline alone, and were ligated following a similar interval, had an average DFI of 14.0 and 31.9 percent viable tissue. Among the subjects that were ligated at 3 days, only a single, gene-infused flap had any noticeable viable tissue after 7 days. The DFI of these groups was 11.0 for the gene-infused group and 22.1 for the saline-infused group. The results suggest that delivery of the gene for VEGF can improve the survival of ischemic skin flaps, but that the effect of gene therapy is not limitless.

Dynamic cortical activity in the human brain reveals motor equivalence

That animals and humans can accomplish the same goal using different effectors and different goals using the same effectors attests to the remarkable flexibility of the central nervous system. This phenomenon has been termed 'motor equivalence', an example being the writing of a name with a pencil held between the toes or teeth. The idea of motor equivalence has reappeared because single-cell studies in monkeys have shown that parameters of voluntary movement (such as direction) may be specified in the brain, relegating muscle activation to spinal interneuronal systems. Using a novel experimental paradigms and a full-head SQUID (for superconducting quantum interference device) array to record magnetic fields corresponding to ongoing brain activity, we demonstrate: (1), a robust relationship between time-dependent activity in sensorimotor cortex and movement velocity, independent of explicit task requirements; and (2) neural activations that are specific to task demands alone. It appears, therefore, that signatures of motor equivalence in humans may be found in dynamic patterns of cortical activity.

Neural network classifications and correlation analysis of EEG and MEG activity accompanying spontaneous reversals of the Necker cube

It has recently been suggested that reentrant connections are essential in systems that process complex information [A. Damasio, H. Damasio, Cortical systems for the retrieval of concrete knowledge: the convergence zone framework, in: C. Koch, J.L. Davis (Eds.), Large Scale Neuronal Theories of the Brain, The MIT Press, Cambridge, 1995, pp. 61-74; G. Edelman, The Remembered Present, Basic Books, New York, 1989; M.I. Posner, M. Rothbart, Constructing neuronal theories of mind, in: C. Koch, J.L. Davis (Eds.), Large Scale Neuronal Theories of the Brain, The MIT Press, Cambridge, 1995, pp. 183-199; C. von der Malsburg, W. Schneider, A neuronal cocktail party processor, Biol. Cybem., 54 (1986) 29-40]. Reentry is not feedback, but parallel signalling in the time domain between spatially distributed maps, similar to a process of correlation between distributed systems. Accordingly, it was expected that during spontaneous reversals of the Necker cube, complex patterns of correlations between distributed systems would be present in the cortex. The present study included EEG (n=4) and MEG recordings (n=5). Two experimental questions were posed: (1) Can distributed cortical patterns present during perceptual reversals be classified differently using a generalised regression neural network (GRNN) compared to processing of a two-dimensional figure? (2) Does correlated cortical activity increase significantly during perception of a Necker cube reversal? One-second duration single trials of EEG and MEG data were analysed using the GRNN. Electrode/sensor pairings based on cortico-cortical connections were selected to assess correlated activity in each condition. The GRNN significantly classified single trials recorded during Necker cube reversals as different from single trials recorded during perception of a two-dimensional figure for both EEG and MEG. In addition, correlated cortical activity increased significantly in the Necker cube reversal condition for EEG and MEG compared to the perception of a non-reversing stimulus. Coherent MEG activity observed over occipital, parietal and temporal regions is believed to represent neural systems related to the perception of Necker cube reversals.

A MEG analysis of the P300 in visual discrimination tasks

Based on recent research that indicated that P300 scalp topography varies as a function of task and/or information to be processed, this study examined scalp-recorded magnetic fields correlated with the P300 by means of whole-head magnetoencephalography. Subjects performed two discrimination tasks, in which targets, defined on either object or spatial characteristics of the same visual stimuli, had to be discriminated. Based on the across-subject root mean square (RMS) functions a sequence of 4 components could be identified in both tasks, N1m, P3m, and two later components, which, based on their estimated neuronal sources, were classified as representing motor processes during and following the manual responses to target stimuli. Reliable between-task differences in source localization were obtained for the P3m component, but not for the other components. Inferior-medial sources were found for the P3m evoked by both spatial and object targets, with these sources being located about 3.5 cm more anterior for object targets. These results suggest that different neuronal sources, possibly located in subcortical regions in the vicinity of the thalamus, contribute to the P3m evoked by target stimuli defined by either object or spatial stimulus characteristics.

Sensory feedback contributes to early movement-evoked fields during voluntary finger movements in humans

Neuromagnetic field changes accompanying voluntary movement in humans ('movement-evoked fields' or MEFs) were recorded over the scalp using a whole-head MEG system during the performance of self-paced finger movements in order to determine the contribution of sensory feedback to the generation of these brain responses. It was found that cooling the subject's arm resulted in delays of 8 ms or more in the latency of the early movement-evoked field component (MEFI). These delays were attributed to increases in conduction times in the afferent pathways as confirmed by electrically evoked somatosensory responses and suggest a peripheral origin of the MEFI. In a second experiment, we demonstrated the effects of sensory input to the contralateral hand during a simple button pressing task in 4 subjects. The results indicated that responses over the hemisphere ipsilateral to the side of movement which resembled previously reported ipsilateral MEFs can be elicited by the spread of mechanical stimulation to opposite side of the body when a mechanical trigger is used. These experiments provide further evidence that early movement-evoked fields produced by unilateral finger movements are observed primarily over the contralateral somatosensory cortex and represent sensory feedback to the somatosensory cortex from the periphery.

The development of a Marjolin's cancer in a human immunodeficiency virus-positive hemophilic man and review of the literature

BACKGROUND

The malignant potential of chronic ulcers and scars secondary to a variety of injuries is well characterized in the medical literature. Furthermore, it has been reported that human immunodeficiency virus (HIV)-positive patients have a higher incidence of basal cell carcinoma (BCC) than the general population.

OBJECTIVE

To describe a case of an unusually aggressive morpheaform BCC that developed in a 28-year-old HIV-positive patient. The tumor developed in a scar 25 years after the initial trauma (Marjolin's ulcer).

METHODS

Description of a case and review of the literature of Marjolins ulcer.

RESULTS

The tumor was removed in a seven-stage, 21-section, micrographically controlled excision. Intraoperatively, perineural invasion of the infraorbital nerve was observed. The postoperative defect was repaired using a full-thickness skin graft.

CONCLUSION

Although most malignancies arising within chronic scars are SCCs, BCCs and a number of other tumors have been described. Mohs micrographic surgery was effective in treating this aggressive morpheaform BCC. A high degree of suspicion in any changing healed scar is recommended.

Continuous tissue oxygen tension measurement as a monitor of free-flap viability

Early recognition of vascular compromise within microvascular free-tissue transfers is essential if reexploration is to prove successful. Tissue oxygen tension is increasingly recognized to be a sensitive and reliable index of tissue perfusion, and preliminary studies suggest that it may be of value in the assessment of free-flap viability. We describe our investigation into the application of an implantable microcatheter oxygen sensor in the monitoring of free flaps used in head and neck and extremity reconstruction. In a preliminary study using the rabbit model, we sought to evaluate the response of oxygen tension as an index of tissue perfusion in myocutaneous (n = 20) and osteomyocutaneous flaps (n = 5) under conditions of arterial and venous occlusion. A clinical study was then undertaken to evaluate the role of this method in the monitoring of surface and buried free flaps. In 30 heterogeneous free-tissue transfers, sensors placed intraoperatively were used to provide continuous information about flap oxygen tension (mean monitoring period 3.2 +/- 0.8 days). The data generated were correlated with changes in clinical parameters and routine flap observations. Results for experimental and clinical data have confirmed the efficacy of continuous tissue oxygen measurements using this device as a method that provides an objective, recordable index of free-tissue transfer viability in a variety of circumstances and vascular events. Tissue oxygen tension is a suitable index by which to evaluate flap viability with the probe placed in muscle or bone but is unreliable when used for the monitoring of revascularized cutaneous flaps.

Reappraisal of the inferior epigastric flap: a new neurovascular flap model in the rat

An anatomic, histologic, and electrophysiologic study was carried out in order to determine the distribution and cutaneous sensory territory of the epigastric nerve in the rat. Results for nerve staining (Sihler's method) and electrophysiologic nerve mapping indicate that the neurosome of the epigastric nerve has a different autonomy than the vascular territory of the inferior epigastric artery. Based on these findings, an experimental model for neurovascular free-tissue transfer is proposed.

Periadventitial delivery of heparin in the prevention of microvenous thrombosis

PURPOSE

In spite of advances in technique and instrumentation, microvascular free tissue transfer remains associated with a persistent risk of flap failure. The use of systemic anticoagulants to overcome the formation of vasoocclusive thrombi at reactive anastomotic sites is associated with a high rate of flap hematoma and is ill advised in the operative setting. The purpose of this study was to investigate the use of a biodegradable, nontoxic polymer gel (polyvinyl alcohol, PVA) to effect a sustained localized release of perivascular heparin around thrombogenic venous anastomoses.

MATERIALS AND METHODS

A modified adventitial inclusion model was created in the femoral vein of 64 adult female Sprague-Dawley rats. Animals were divided into four experimental groups: 1) no treatment (controls), 2) periadventitial PVA gel contained in a vicryl chamber, 3) periadventitial PVA gel mixed with heparin, and 4) systemic heparin (intravenous pump). Patency rates in the femoral vein were checked at 10 minutes, 1 hour, 1 day, and 4 days after surgery. Systemic coagulation parameters and histology (scanning electron microscopy, SEM) were assessed in representative animals from all groups.

RESULTS

Patency rates for experimental groups showed a significant improvement in animals treated with PVA/heparin and systemic heparin over controls. Wound hematomas occurred in 7 of 16 animals in group 3, and in 4 of 16 animals in group 4. Activated partial thromboplastin times were elevated in group 4 only (> 150 seconds).

CONCLUSIONS

Continuous release of periadventitial heparin using a polymeric delivery system may represent an efficient means of attenuating the reactivity of microvenous anastomoses without affecting systemic coagulation parameters. In this model, however, its use was associated with a high rate of local wound hematoma.

Combination therapy for salvaging a failing, experimental skin flap

The failing free flap remains a major problem for the reconstructive surgeon. Many and varied pharmacologic agents have been utilized to reverse the effects of ischemia in these flaps. Treatments have been aimed at inhibiting presumed causative factors in the no-reflow phenomenon. Therapy has generally been single in nature and designed to affect only one of these presumed factors. In this study, several pharmacologic agents were utilized individually or in combination therapy as postischemic washouts, in an effort to attack the multiple causative factors in the no-reflow phenomenon and to improve flap survival in a rat abdominal skin flap model. The treatment agents included lactated Ringer's, superoxide dismutase, and urokinase, with each used independently as a postischemic perfusion washout. Combination therapy utilized an initial postischemic perfusion with urokinase, followed by a second perfusion washout with superoxide dismutase. After 18 hr of primary ischemia, there was increased flap survival in the animals undergoing perfusion washout with either superoxide dismutase alone or with combined urokinase and superoxide dismutase washouts, compared to all other treatments (p < 0.001). It was found that flaps undergoing combined urokinase and superoxide dismutase postischemic perfusion washouts demonstrated significantly improved survival after 20 hr of primary ischemia, compared to all other therapies (p < 0.05). By demonstrating improved survival when a thrombolytic agent is used in conjunction with an oxygen free radical scavenger, these findings may have implications in the treatment of clinically failing free flaps.

Beneficial effects of corticosteroids on ocular myasthenia gravis

OBJECTIVE

To determine if moderate-or low-dose corticosteroid therapy can reduce the diplopia and frequency of deterioration to generalized disease in ocular myasthenia gravis.

DESIGN

Retrospective record review.

SETTING

Two university-based neuro-ophthalmology services.

PATIENTS

All 32 patients with ocular myasthenia gravis, treated with prednisone, followed up for a minimum of 2 years were included. Patients were treated with 1 or more courses of daily prednisone (highest initial dose, 40-80 mg) gradually withdrawn over 4 to 6 weeks. Subsequently, in 6 patients, 2.5 to 20 mg of prednisone was given on alternate day.

OUTCOME MEASURES

Diplopia in the primary position or downgaze diplopia and generalized myasthenia gravis after 2 years of follow-up.

RESULTS

Diplopia, which was initially found in the primary position in 29 patients and in the downgaze position in 26 patients, was absent in 21 patients at 2 years. Generalized myasthenia gravis occurred in 3 patients at 2 years. Elevated serum acetylcholine receptor antibody levels and abnormal electromyography findings were not predictive of worsening. No patient experienced a major steroid complication.

CONCLUSIONS

Moderate-dose daily prednisone for 4 to 6 weeks, followed by low-dose alternate-day therapy as needed, can control the diplopia in patients with ocular myasthenia gravis. The frequency of deterioration to generalized myasthenia gravis at 2 years may be reduced; 9.4% in this study compared with more than 40% previously reported frequency. Corticosteroids may be useful even when ocular motor dysfunction is not normalized.

Increased patency of artificial microvascular grafts using arteriovenous fistula loops: a two-stage procedure for lengthening the pedicle of free-tissue transfer

The effect of a high-flow system on the patency of artificial microvascular grafts (AMG) was investigated using arteriovenous (A-V) fistula loops made of polytetrafluoroethylene (PTFE) in a clinically useful longer length. At a second stage, the A-V loops, matured for 7 days, were used as recipient conduits for free-tissue transfer. The patency rates of 5-cm long PTFE A-V fistula loops were compared with 5-cm and 1-cm long interpositional micrografts in a rat model. The patency rate of the loops at 7 days was 80 percent, compared to 0 percent for both the 5-cm and 1-cm interpositional grafts. A-V fistula loops matured for 7 days in vivo were divided in their midsections and used as arterial and venous conduits (each 2.5 cm long) for free epigastric flaps (3 x 6 cm) raised from the contralateral groin. Sixty-seven percent (8/12) of the free flaps were viable at 7 days. The A-V fistula loop in a high-flow system has a beneficial effect in maintaining patency of AMGs. PTFE fistula loops matured for 7 days can be used as arterial and venous conduits for microsurgical tissue transfer in rats.

Thrombolysis at a controlled pressure prolongs the survival of skin flaps treated with superoxide dismutase

The role of thrombolysis in reestablishing patency in the microcirculation following ischemia, and thereby improving the efficacy of agents attenuating reperfusion injury, such as the oxygen free radical scavenger, superoxide dismutase (SOD), was investigated in a rat model. Abdominal skin flaps were subjected to normothermic ischemia induced by complete occlusion of the pedicle for periods of 12, 13, 14, 16, 18, 20, 22, and 24 hr. In Group 1 (n = 64), all animals received flap washout using 100,000U urokinase (manual injection) followed by 7,500 IU SOD given intra-arterially immediately prior to reperfusion. Animals in Group 2 received flap washout consisting of 100,000U urokinase given via a pressurized delivery system, followed by 7,500 IU SOD. Results demonstrated a statistically significant improvement in flap survival in Group 2. The authors concluded that thrombolytic therapy may be useful in improving the delivery of agents, such as SOD, which attenuate reperfusion injury in skin flaps.

Additional benefit of heparin in the thrombolytic salvage of ischemic skin flaps

Microvascular thrombosis is known to play an important part in the cessation of flow seen in a flap following ischemia and revascularization. Its reversal, using thrombolytic therapy, is associated with higher rates of successful flap salvage. Although this procedure restores patency to the microcirculation, the damaged endothelial cell layer remains highly thrombogenic and a definite risk of rethrombosis exists in the early period of reperfusion. In an inferior epigastric flap model in a rat, we investigated the effect of additional heparin (subcutaneous and intravenous administration) following a standardized urokinase washout (100,000 iu) of the ischemic flaps. Flap survival was assessed at 1 week and morphological changes in the microcirculation were observed using electron microscopy. Results showed a significant increase in flap survival in the group receiving intravenous heparin following urokinase washout and suggest that systemic heparin may play a beneficial role in the early reperfusion period following thrombolytic flap salvage.

A standardized model of microvenous thrombosis

A standardized model of venous thrombosis is necessary when evaluating potential antithrombotic or thrombolytic agents in microsurgery. Previous studies have shown the adventitial "tuck" model to be advantageous in terms of the vascular reactivity achieved and the relative ease of performance. However, variability exists in the current design, due to the lack of standardized dimensions of the adventitial flap. Two variations of this model are presented which attempt to overcome this problem, and their reproducibility is compared to the inversion graft model of venous thrombosis in the rat femoral vein. The "femoral vein flap" is suggested as a suitable model to simulate anastomotic thrombosis during microvenorrhaphy.

Evaluation of a continuous systemic infusion of iloprost, a stable PGI-2 analog, on the survival of experimental skin flaps

Numerous investigators have attempted to enhance the survival of ischemic experimental skin flaps using various pharmacologic manipulations. Recently, the authors' laboratory demonstrated the beneficial effect of iloprost, a stable PGI2 analogue, as a post-ischemic perfusion washout, in improving the survival of ischemic skin flaps. The rat unilateral abdominal skin flap, based on the superficial epigastric vessels, was utilized in this study involving 30 animals. The animals were divided into three different treatment groups, with ischemic periods of 16 and 18 hr. Perfusion washouts were performed at the completion of the various ischemic periods. Alzet osmotic pumps were used to deliver a continuous systemic infusion of iloprost for 7 days postoperatively. The groups consisted of the following: Group 1 (single ILO)--perfusion washout with iloprost only; Group 2 (continuous LD ILO)--low-dose systemic iloprost infusion (0.066 mcg/kg/min) and perfusion washout with iloprost; and Group 3 (continuous HD ILO)--high-dose systemic iloprost infusion (0.1 mcg/kg/min) and perfusion washout with iloprost. The percentage of flap survival was assessed on postoperative day 7. Skin flaps of the animals receiving the continuous systemic infusion of iloprost were noted to have varying percentages of survival, while skin flaps undergoing perfusion washout only were found to have either complete survival using a continuous systemic infusion of iloprost, compared to iloprost perfusion washout alone. In addition, the hypotensive side effects of systemic iloprost infusion limit its use in the rat skin-flap model.