Diagnosis of progressive compression of the aortic true lumen with intraoperative transesophageal echocardiography during repair of dissection of thoracic aorta--a case report

We report an incident of progressive compression of the true lumen of aorta which happened immediately after cardiopulmonary bypass (CPB) and was diagnosed with intraoperative transesophageal echocardiography (TEE) in a patient undergoing an emergent repair of type A aortic dissection under femoral perfusion. During the CPB period, intraoperative TEE revealed gradual expansion of the false lumen which nearly obstructed the true lumen of the dissected aorta. The possible mechanism was related with distension of the false lumen by a dominant flow from retrograde femoral perfusion of CPB. With the application of intraoperative TEE, we could easily detect the hemodynamic changes of thoracic aorta and find the real causes so as to solve the perfusion abnormalities.

Risk factors for pneumothorax and bleeding after CT-guided percutaneous coaxial cutting needle biopsy of lung lesions

PURPOSE

To evaluate risk factors for pneumothorax and bleeding after computed tomography (CT)-guided percutaneous coaxial cutting needle biopsy of lung lesions.

MATERIALS AND METHODS

This study involved 117 consecutive patients with 117 intrapulmonary lesions. Statistical analysis of factors related to patient characteristics, lung lesions, and biopsy technique was performed to determine possible contribution to the occurrence of pneumothorax and bleeding. Interactions between related factors were considered to prevent colinearity.

RESULTS

Pneumothorax occurred in 12% (14 of 117) of patients. Needle aspiration of two moderate asymptomatic pneumothoraces were performed; there was no chest tube insertion. Lesion depth (P =.0097), measured from the pleural puncture site to the edge of the intrapulmonary lesion along the needle path, was the single significant predictor of pneumothorax. The highest risk of pneumothorax occurred in subpleural lesions 2 cm or shorter in depth (this represented 33% of lung lesions but caused 71% of all pneumothoraces; OR = 7.1; 95% CI, 1.3-50.8). Bleeding presented as lung parenchyma hemorrhage and hemoptysis in 30 patients (26%). Hemoptysis occurred in four patients (3%). Univariate analysis identified lesion depth (P <.0001), lesion size (P <.015), and pathology type (P =.007) as risk factors for bleeding. Multivariate logistic regression analysis identified lesion depth as the most important risk factor, with the highest bleeding risk for lesions more than 2 cm deep (14% of lesions caused 46% of all bleeding; OR = 17.3; 95% CI, 3.3-121.4).

CONCLUSIONS

In CT-guided coaxial cutting needle biopsy, lesion depth is the single predictor for risk of pneumothorax, which occurs at the highest rate in subpleural lesions. Increased risk of bleeding occurs in lesions deeper than 2 cm.

Minimal access thoracic surgery for esophageal hemangioma

Esophageal hemangioma is a rare tumor. This report describes the case of a 69-year-old woman with an esophageal tumor at the middle portion of the esophagus. The patient was successfully treated with minimal access thoracic surgery, and at the 6 month follow-up, the patient was free of any symptoms or recurrence.

The intubating laryngeal mask airway in severe ankylosing spondylitis

PURPOSE

To evaluate the use of inhalational induction followed by intubation through the intubating laryngeal mask (ILM) for patients with severe ankylosing spondylitis undergoing elective surgery who prefer airway management under anesthesia.

METHODS

Nine patients undergoing a total of 11 procedures were enrolled in the study. Fentanyl 2 microg*kg(-1), midazolam 0.035 mg*kg(-1) and sevoflurane in oxygen 100% were used for induction. The ILM was inserted when the end-tidal sevoflurane concentration reached 3%. After an effective airway was established, atracurium 0.5 mg*kg(-1) was given. A polyvinyl chloride tube in the reversed position using a blind technique was used to intubate the trachea.

RESULTS

The ILM provided an effective airway on 11/11 occasions at the first attempt. Intubation was successful at the first attempt on 7/11 occasions, at the second attempt on 2/11 and at the third attempt in 1/11. Intubation failed in one patient. The mean (range) minimal oxygen saturation was 99.4% (97-100%). There were no problems with ILM removal.

CONCLUSION

Inhalational induction followed by ILM insertion and blind intubation is a reasonable option in patients with severe ankylosing spondylitis undergoing elective surgery who prefer airway management under anesthesia.

Phylogenetic relationships of the Cochliopinae (Rissooidea: Hydrobiidae): an enigmatic group of aquatic gastropods

Phylogenetic analysis based on a partial sequence of the mitochondrial cytochrome c oxidase subunit I gene was performed for 26 representatives of the aquatic gastropod subfamily Cochliopinae, 6 additional members of the family Hydrobiidae, and outgroup species of the families Rissoidae and Pomatiopsidae. Maximum-parsimony analysis yielded a single shortest tree which resolved two monophyletic groups: (1) a clade containing all cochliopine taxa with the exception of Antroselates and (2) a clade composed of Antroselates and the hydrobiid genus Amnicola. The clade containing both of these monophyletic groups was depicted as more closely related to members of the family Pomatiopsidae than to other hydrobiid snails which were basally positioned in our topology. New anatomical evidence supports recognition of the cochliopine and Antroselates-Amnicola clades, and structure within the monophyletic group of cochliopines is largely congruent with genitalic characters. However, the close relationship between the Pomatiopsidae and these clades is in conflict with commonly accepted classifications and suggests that a widely accepted scenario for genitalic evolution in these snails is in need of further study.

Report of the consensus conference on diagnostic criteria of ALI/ARDS at high altitudes in Western China

China is a mountainous country. The Qing-Zang plateau, Yun-Gui plateau, and Yellow Land plateau, which are known as the world's ridge, are located in the west of China. The highland area over 3,000 m in height occupies one-sixth of the land area of China and half the highland area of the world. About 60-80 million people live in the regions where the elevation ranges from 1,500 m to 4,000 m. In the latter half of the last century, the influence of complex environmental factors on the human body, such as low oxygen pressure, cold climate, strong radiation, high wind speed, and super-evaporation, were studied in an extensive and profound way and formed an important field of altitude medicine. For a long time, many researchers have carried out investigations related to the systemic inflammatory response syndrome (SIRS), acute respiratory distress syndrome (ARDS), and multiple organ dysfunction syndrome (MODS) and its pathophysiological mechanism initiated by cytokines and mediators, regarding which many problems are still unclear. However, systematic research into the mechanism from SIRS to ARDS to MODS in the highlands remains blank. The diagnostic criteria of ALI/ARDS in the highlands are quite different from that in the plain, and thus was a central topic for discussion at this meeting.

Sustained microglial immunoreactivity in the caudal spinal trigeminal nucleus after formalin injection

Recent studies indicate that glia may be involved in altered nociceptive processing after a peripheral inflammatory lesion produced by injection of inflammatory reagents such as formalin and zymosan. Most of these studies, however, confined their observations to a period shortly after the injections. This study investigated the immunohistochemical responses of microglia in the caudal part of the spinal trigeminal nucleus for up to 60 days after subcutaneous injection of formalin into the lateral faces of Wistar rats. The results showed obvious up-regulation of microglial markers such as OX-18, OX-42 and OX-6 up to 21 days after formalin injection. These were somewhat reduced at 30 days after injection. Electron microscope investigation revealed no evidence of significant phagocytosis of degenerative neuronal elements by microglia in the nucleus at the time--that is, 7 days after formalin injection, when microglial activation was at its peak. Significantly, however, the period of microglial activation corresponded closely to that showing enhanced nociceptive behavior after perioral formalin injection (Cadet et al., 1995). This study indicates a microglial role in the genesis of enhanced nociceptive behavior.

[The development of a device producing brain injury by gas percussion]

The device is developed based on aerodynamical principle, measuring technique for feeble signal, and mechano-electronic integration. The left parietals of rats were made cranioectomy and injured by different pressure of gas source with the device and then the survival states, pathological changes and neurobehavioral changes of rats were observed.

Thoracoscopic retrieval of metal rods after penetrating chest injury: case report

Thoracoscopy has been used for both diagnostic and therapeutic purposes. Its use in the trauma field is rapidly increasing. Here, we present a case of chest trauma that was successfully treated using the thoracoscopic approach. A 43-year-old male patient was brought to our emergency room with a severe right chest wall-penetrating metal-rod injury, which had occurred after falling from a height. The chest X-ray showed an upper right lung lobe injury. Video-assisted thoracoscopic surgery (VATS) was performed for diagnosis of any other associated injury and for management of the penetrating injury. The prognosis was good. We believe that minimal thoracoscopic surgery is an alternative way that provides a more rapid diagnosis, and a less-invasive and safe operation for acute chest trauma patients.

Paradoxical cerebral air embolism after removal of a central venous catheter: case report

Paradoxical cerebral air embolization through a residual tract after the removal of a central venous catheter is a serious complication of central venous cannulation. Air embolisms resulting from residual catheter tracts in general patients and in single lung transplant patients have been reported. The generally accepted mechanism of this complication is failure of a spontaneous collapse or thrombotic obliteration of a well-formed catheter tract. It may be related to the duration of catheter insertion, the patient's nutritional status, the diameter of the indwelling catheter, the upright position of the patient, deep inspiration or coughing, and improper wound dressing and catheter removal. Cardiovascular collapse, pulmonary or neurologic sequelae, and even death, are commonly noted in patients with air embolism. In this article, we report on cerebral air embolization as a complication with the removal with a central venous catheter in a patient with bullous emphysema. A high degree of suspicion and a prompt diagnosis are required for successful application of established therapy. Simple prophylactic procedures and constant awareness of the unusual mechanism of air embolism remain the best treatment.

Video-assisted thoracoscopic surgery in managing tuberculous spondylitis

The literature includes no studies on the use of video-assisted thoracoscopic surgery in the management of tuberculous spondylitis, and its role in the management of tuberculosis involving the thoracic spine remains unclear. The authors experience with 10 consecutive patients (six women, four men) who underwent video-assisted thoracoscopic surgery for the treatment of spinal tuberculosis involving levels from T5 to T11, from January 1996 to December 1997, was analyzed. Using the extended manipulating channel method (2.5-3.5 cm portal incisions), video-assisted thoracoscopic surgery was performed with a three-portal technique (seven patients) or a modified two-portal minithoracotomy technique that required a small incision for the thoracoscope and a larger incision, measuring 5 to 6 cm, for the procedures in three patients. All the patients were studied prospectively. The followup ranged from 17 to 42 months (mean, 24 months). Postoperative complications included one lung atelectasis. Pleural adhesions, owing to local inflammation or paravertebral abscess, were seen in four patients and one patient with severe pleurodesis needed an open technique for treatment. Postoperative air leaks were seen in four (40%) of 10 patients but all were transient. The average neurologic recovery was 1.1 grades on the Frankel's scale. The data from this series of patients with tuberculous spondylitis show that video-assisted thoracoscopic surgery has diagnostic and therapeutic roles in the management of tuberculous spondylitis. Technically, a combination of thoracoscopy and conventional spinal instruments to perform video-assisted thoracoscopic surgery through the extended manipulating channels, which were placed slightly more posterior than usual, was effective and safe.

Anesthesia of CO2 laser surgery in a patient with Hunter syndrome: case report

Hunter syndrome (mucopolysaccharidosis, type II; MPS II) is one of a heterogeneous group of recessively inherited mucopolysaccharide storage diseases. Patients with mucopolysaccharidosis show progressive involvement and derangement of many organs, especially upper airway anomalies, which are the major cause of perioperative death. In recent years, a CO2 laser is often applied to upper airway lesions. A 16-year-old patient suffering from Hunter syndrome was scheduled for CO2 laser surgery because of sleep apnea and respiratory stridor. Otolaryngological examination revealed bulging of the bilateral false cord with stenosis of the glottis. We adopted sevoflurane mask induction and high-frequency jet ventilation to overcome the perioperative airway problems. The anesthetic course was uneventful, and the patient was discharged 2 days after the operation.

Spontaneous pneumothorax in children

Sixteen consecutive children diagnosed with spontaneous pneumothorax (SP) and admitted to Chang Gung Children's Hospital between July 1994 and June 1999 were retrospectively studied. The presenting features, radiographic abnormalities, and indications of surgery were reviewed. All patients were exclusively adolescents and were aged between 12 and 17 years. Six patients received chest tube drainage only. Nine patients underwent ablation of blebs or bullae using video-assisted thoracoscopic surgery (VATS) with good results. One patient had a bullous emphysema removed by wedge resection. One patient with spontaneous hemopneumothorax required a blood transfusion and emergent thoracotomy for stabilization. Computed tomographic (CT) scans of the chest detected all seven (100%) cases with apical bulla formations. First episodes of spontaneous pneumothorax were treated conservatively using closed-tube thoracostomy if the plain chest radiographs and CT scans were negative for apical bleb or bulla formations. In summary, SP occurred exclusively in adolescents in this study, commonly they had no underlying pulmonary abnormalities except for bulla or bleb formations. SP can be safely and effectively managed using VATS and abrasive pleurodesis in children without recurrence at follow-up. SP may be treated surgically even in the first event of pneumothorax when subpleural blebs are demonstrated by high-resolution computed tomographic scans.

Necrotising pneumonitis in children

We retrospectively analysed the clinical features and outcome of children under 17 years of age with necrotising pneumonitis (NP). The radiographs and CT scans of the chest of children under 17 years of age between July 1995 and March 1999 who had complicating community-acquired pneumonia were reviewed. CT scans were obtained for persistent fever, respiratory distress and sepsis despite empiric antibiotic therapy and closed tube drainage. A total of 21 children had the radiographic features of NP of whom 11 (52%) patients were successfully managed using antibiotic therapy with or without closed tube drainage. Ten patients required thoracoscopic decortications and/or lysis of pleural adhesions or debridement of empyema due to refractory pleural sepsis, failure of pulmonary re-expansion and persistent air-leaks. The most common pathogens identified were Streptococcus pneumoniae (n = 3), Staphylococcus aureus (n = 2), and Haemophilus influenzae type b (n = 2). The days of hospital stay, duration of fever and days of C-reactive protein return to normal were significantly less for the medically versus the surgically treated children (P < 0.05).

CONCLUSION

The clinical course of necrotising pneumonitis in children following complicated pneumonia is often prolonged despite adequate antibiotic therapy. Necrotising pneumonitis with co-existing multiple loculations, pneumothorax/ bronchopleural fistula in the empyema and extensive pleural peel are poor prognostic factors for medical therapy. Thoracoscopic removal of loculated empyema, lysis of adhesions and/or decortication are effective in relieving tachypnoea, chest pain, and controlling fever and improve the outcome, especially in children with empyema.

Contributions of protein disulfide isomerase domains to its chaperone activity

Protein disulfide isomerase (PDI), a member of the thioredoxin (Trx) superfamily, consists of five consecutive domains, a-b-b'-a'-c. Domain combinations, AB, A'C, B'A'C and AB-C, and hybrids of PDI domains with Trx, Trx-C and Trx-B'A'C, have been constructed and expressed in Escherichia coli to examine the contributions of PDI domains to its enzyme and chaperone activities. All the combination and hybrid products are considerably less active than intact PDI in their enzyme activities. Recombinant products containing C, at low concentrations, inhibit the reactivation of lysozyme in HEPES buffer, while those without C do not. Only the intact PDI molecule and the hybrid molecule, Trx-B'A'C, but to a much lower level, show general chaperone activity in assisting the reactivation of denatured D-glyceraldehyde-3-phosphate dehydrogenase. It is suggested that all domains of PDI contribute to the binding of target protein for its chaperone activity.

Thoracoscopic removal of intrathoracic neurogenic tumors: a combined Chinese experience

OBJECTIVE

To review the surgical and clinical results of minimally invasive resection of intrathoracic neurogenic tumors using a video-assisted thoracoscopic technique.

SUMMARY BACKGROUND DATA

Thoracoscopy has emerged as a possible means for diagnosing and managing various intrathoracic disorders. Benign intrathoracic tumors often are ideal lesions for resection using a video-assisted technique. The authors report on their combined experience with the thoracoscopic resection of 143 intrathoracic neurogenic tumors.

METHODS

Between March 1992 and February 1999, 143 patients with intrathoracic neurogenic tumors were diagnosed and underwent resection using video-assisted thoracoscopic techniques in three teaching centers. Case selection, surgical technique, and clinical results were reviewed.

RESULTS

The average age of the patients was 40.8 years; 57.3% were male. Thirty-eight patients (27%) had symptoms attributable to the masses. Seventy-two masses were neurofibromas, 33 were neurilemmomas, 7 were paragangliomas, and 31 were ganglioneuromas. All but seven tumors were located in the posterior mediastinum. The masses were on average 3.5 cm in greatest diameter. The mean surgical time was 40 minutes, and the average hospital stay was 4.1 days. There were no major postoperative complications or recurrences to date. Nine patients reported paresthesias over the chest wall during a mean follow-up of 29 months.

CONCLUSIONS

Resection of intrathoracic neurogenic tumors using a thoracoscopic technique based on standard surgical indications would seem to be appropriate. Most of these masses are benign and readily removed. For dumbbell tumors, a combined thoracic and neurosurgical approach is mandatory.

Cost-effective approach of video-assisted thoracic surgery: 7 years experience

BACKGROUND

Cost containment is the driving force behind current health care reform. While video-assisted thoracic surgery (VATS) permits a less invasive approach to surgical diseases of the chest, cost is one aspect that is seldom discussed. In Asia, cost-effectiveness essential for the survival of this approach. We present our cost-effective experience with VATS in 2300 patients over a 7-year period.

METHOD

Between 1992 and 1999, 2300 patients underwent video-assisted thoracic surgery at Chang Gung Memorial Hospital. The mean age was 53.2 years (range, 22 days to 102 years); 67% (1541 patients) were men. The VATS technique was mainly performed based on traditional surgical principles. Conventional instruments and the fundamental surgical techniques of dissection, suturing, hemostasis, and tissue approximation that are familiar in the open setting were modified and used to enhance cost savings during VATS.

RESULTS

Surgery was performed on 41 patients on an emergency basis (24 with impending cardiac tamponade and 17 with hemothorax). The mean hospital stay of the patients treated by VATS was 4.5 days. The majority of the patients were operated on successfully using conventional instruments under video vision. The overall operative cost was decreased as compared to common VATS techniques. No delayed morbidity was noted in our patients after a mean follow-up period of 39 months (range, 1 to 68 months).

CONCLUSION

It is our experience that VATS procedures should be performed with the same expertise as open surgery. Conventional instruments similar to those used in open thoracotomy can be incorporated in VATS, and with a more natural hand manipulation. Only through stringent use of expensive endoscopic consumables and application of modified techniques based on traditional surgical principles can VATS be performed efficaciously and economically for a wide range of thoracic conditions.

Catamenial hemoptysis: report of a case treated with thoracoscopic wedge resection

Catamenial hemoptysis is a rare form of hemoptysis. It is a term for the condition of hemoptysis associated with menses. Few cases have been reported in the literature. Only one case, treated by video-assisted thoracoscopic wedge resection, has been described. We report the case of a 26-year-old woman who suffered from catamenial hemoptysis for 7 months and was treated successfully with a video-assisted thoracoscopic (VATS) wedge resection of the lesion. No evidence of recurrence was noted in the postoperative follow-up period of 48 months. We suggest that VATS is the good choice for single focus catamenial hemoptysis.

'Needlescopic' video-assisted thoracic surgery for palmar hyperhidrosis

OBJECTIVE

The video-assisted thoracic surgery (VATS) approach for thoracodorsal sympathectomy has been well accepted. We report the use of ultra-fine thoracoscopic equipment for this procedure, based on the experience from two centers in Asia.

MATERIALS AND METHODS

Thirty-eight patients with palmar hyperhidrosis underwent bilateral VATS thoracodorsal sympathectomy using 2-mm instruments exclusively. General anesthesia with selective one lung ventilation was used. Carbon dioxide insufflation was used when lung collapse was found to be inadequate. In 11 patients, the sympathetic chain was excised (T2-T3 for palmar hyperhidrosis alone, extending to T4 for axillary hyperhidrosis), and in 27 patients, the chain was cauterized. The choice of procedure reflects the surgeon's preference. No chest drains were left after the procedure and no stitching of the wound was necessary.

RESULTS

There was no mortality or major complications. A small pneumothorax was found in the postoperative chest X-ray in three patients. They all resolved without further intervention. Twenty-seven patients were discharged on the same day of admission, and 11 patients were discharged on postoperative day one. After an average follow-up of 16 months (range 5-28), there has been no recurrence of symptoms. Compensatory truncal hyperhidrosis was encountered in two patients, but the symptoms were not severe enough to interfere with lifestyle, and this required no further treatment.

CONCLUSION

Thoracodorsal sympathectomy using 2-mm instruments is technically feasible and is associated with an excellent clinical outcome. Limitations of the equipment, however, exist (narrow field of vision, lower resolution and difficulty in maintaining fine control), and we are currently restricting its use to relatively simple procedures.

[The transfusion and blood transfusion in pediatric patients with palatoplasty]

OBJECTIVE: To study whether the pediatric patients with palatoplasty needs blood transfusion and the rational combination of transfusion during operation,in order to provide a basis for the management of clinical anesthesia and postoperative recovery in children.METHODS:20 subjects without blood transfusion were selected,the combination of transfusion during the operation was 5% glucose solution,sodium lactate ringers solution,gelofusine.The intraoperative and postoperative circulation, hemoglobulin, hematocrit were compared with the preoperative data.RESULTS:Both the intraoperative and the postoperative circulation of all subjects were steady, having no significant difference from the data base(P>0.05), the values of hemoglobulin and hematocrit descended,but were in the normal limit(P>0.05).CONCLUSION: During palatoplasty in pediatric patients, if transfusion was apporpriate, steady circulation can be substained without boold transfusion,which saved the blood, and avoided the side effects of blood transfusion.

Glutamate-induced rise in cytosolic calcium concentration stimulates in vitro rates of juvenile hormone biosynthesis in corpus allatum of Diploptera punctata

We show that in a cockroach, Diploptera punctata, endocrine function of the corpus allatum may be modulated by L-glutamate, a major fast excitatory neurotransmitter in the central nervous system of vertebrates and invertebrates. The widely accepted concept that synthesis of juvenile hormone (JH) depends upon intracellular calcium concentration, is extended by the finding that 60 and 100 microM L-glutamate induces both an increase in calcium concentration in the cytosol of corpus allatum cells, and stimulates JH synthesis in vitro. We show that L-glutamate stimulates JH synthesis by inducing calcium influx since in calcium-free medium the stimulatory effect is not observed. Furthermore, the non-specific glutamate-receptor antagonist, 100 microM kynurenate, and 1.8 mM magnesium, inhibit the stimulatory effect of L-glutamate on JH synthesis in vitro. These results suggest that functional ionotropic glutamate receptors are present on the surface of the cells in corpus allatum, and that rates of JH are at least in part regulated via these receptors.

Thoracoscopic surgery for spontaneous pneumothorax

Spontaneous pneumothorax in apparently healthy individuals is a relatively common occurrence. The management of patients with spontaneous pneumothorax remains controversial. With the advances in thoracoscopic techniques and instrumentation, video-assisted thoracic surgery (VATS) is now accepted by many as the procedure of choice for surgical treatment of spontaneous pneumothorax. We report our combined experience with 757 patients who suffered from recurrent or persistent spontaneous pneumothorax treated by VATS over a 5-year period. Surgical indications included persistent air leak (n = 165), recurrence (n = 325), radiologically demonstrated huge bulla (n = 12), spontaneous hemopneumothorax (n = 13), incomplete expansion of the lung (n = 212), and bilateral involvement (n = 30). Several surgical procedures were undertaken, based on the thoracoscopic findings: endoscopic stapled bullectomy (n = 312), argon beam coagulation (n = 6), endoscopic suturing (n = 52), and endoloop ligation (n = 352). In 49 cases, mechanical or chemical pleurodesis was the only procedure performed. There were no mortalities or intraoperative hazards. Complications consisted of wound infections (n = 16), localized empyema (n = 2), chest wall bleeding (n = 1), and persistent air leaks (bulla type III) (n = 31). The median duration of the operation was 55 minutes (15-160 minutes), and the average postoperative hospital stay was 4.5 days (range 0-27 days). There were 16 recurrences (2.1%), after a mean follow-up of 30 months (range 1-60 months). Seven patients had recurrence from 9 to 17 months after stapled bullectomy. All the remaining patients had recurrence after failed pleurodesis. On the basis of our results, we conclude that video-assisted thoracoscopic management allows effective, safe performance of standard surgical procedures, avoiding a formal thoracotomy incision. We consider thoracoscopy the treatment of choice for patients with pneumothorax requiring surgical therapy.

Phylogenetic relationships within the aquatic snail genus Tryonia: implications for biogeography of the North American Southwest

We examined the phylogenetic relationships among 23 species of the North American aquatic snail genus Tryonia (Hydrobiidae), 10 additional representatives of the subfamily Cochliopinae, and two outgroups. Maximum parsimony analysis of a 601-base-pair sequence from the mitochondrial COI gene did not support monophyly of the genus nor its subgenus Paupertryonia. A clade composed of the type species of Tryonia and 16 congeners was strongly supported by the COI data and congruent with recently discovered variation in female genitalic morphology. This "true Tryonia" clade included two large western subclades having a sister-group relationship. The phylogenetic structure of one of these subclades is congruent with vicariant events associated with late Neogene history of the lower Colorado River drainage. The other subclade mirrors development of the modern Rio Grande rift and inception of modern topography in the southwestern Great Basin during the late Neogene. Both subclades are represented in the composite Tryonia fauna of the Amargosa River basin, whose assembly is attributed to the complex geological history of the Death Valley region.