How effective is laparoscopic redo-antireflux surgery?

BACKGROUND: The failure-rate after primary antireflux surgery ranges from 3 to 30%. Reasons for failures are multifactorial. The aim of this study is to gain insight into the complex reasons for, and management of, failure after antireflux surgery. METHODS: Patients were selected for redo-surgery after a diagnostic workup consisting of history and physical examination, upper gastrointestinal endoscopy, quality-of-life assessment, screening for somatoform disorders, esophageal manometry, 24-hour-pH-impedance monitoring, and selective radiographic studies such as Barium-sandwich for esophageal passage and delayed gastric emptying. Perioperative and follow-up data were compiled between 2004 and 2017. RESULTS: In total, 578 datasets were analyzed. The patient cohort undergoing a first redo-procedure (n = 401) consisted of 36 patients after in-house primary LF and 365 external referrals (mean age: 62.1 years [25-87]; mean BMI 26 [20-34]). The majority of patients underwent a repeated total or partial laparoscopic fundoplication. Major reasons for failure were migration and insufficient mobilization during the primary operation. With each increasing number of required redo-operations, the complexity of the redo-procedure itself increased, follow-up quality-of-life decreased (GIQLI: 106; 101; and 100), and complication rate increased (intraoperative: 6,4-10%; postoperative: 4,5-19%/first to third redo). After three redo-operations, resections were frequently necessary (morbidity: 42%). CONCLUSIONS: Providing a careful patient selection, primary redo-antireflux procedures have proven to be highly successful. It is often the final chance for a satisfying result may be achieved upon performing a second redo-procedure. A third revision may solve critical problems, such as severe pain and/or inadequate nutritional intake. When resection is required, quality of life cannot be entirely normalized.

Primary laparoscopic fundoplication in selected patients with gastroesophageal reflux disease.

BACKGROUND: Despite proton pump inhibitors being a powerful therapeutic tool, laparoscopic fundoplication (LF) has proven successful in the treatment of gastroesophageal reflux disease (GERD), through mechanical augmentation of a weak antireflux barrier and the advantages of minimally invasive access. A critical patient selection for LF, based on thorough preoperative assessment, is important for the management of GERD-patients. The purpose of this study is to provide an overview on the management of GERD-patients treated by primary LF in a specialized center and to illustrate the possible outcome after several years. METHODS: Patients were selected after going through diagnostic workup consisting of patient's history and physical examination, upper gastrointestinal endoscopy, assessment of gastrointestinal Quality of Life Index, screening for somatoform disorders, functional assessment by esophageal manometry, (impedance)-24-hour-pH-monitoring, and selective radiographic studies. The indication for LF was based on EAES-guidelines. Either a floppy and short Nissen fundoplication was performed or a posterior Toupet-hemifundoplication was chosen. A long-term follow-up assessment was attempted after surgery. RESULTS: In total, n = 1131 patients were evaluated (603 males; 528 females; mean age; 48.3 years; and mean body mass index: 27). The mean duration between onset of symptoms and surgery was 8 years. Nissen: n = 873, Toupet: n = 258; conversion rateerativ: 0.5%; morbidity 4%, mortality: 1 (1131). Mean follow-up (n = 898; 79%): 5.6 years; pre/post-op results: esophagitis: 66%/12.1%; Gastrointestinal Quality of Life Index: median: 92/119; daily proton pump inhibitors-intake after surgery: 8%; and operative revisions 4.3%. CONCLUSIONS: In conclusion, our data show that careful patient selection for laparoscopic fundoplication and well-established technical concepts of mechanical sphincter augmentation can provide satisfying results in the majority of patients with severe GERD.

Severity of GERD and disease progression.

BACKGROUND: Many factors may play a role in the severity and progression of gastroesophageal reflux disease (GERD) since pathophysiology is multifactorial. Data regarding the progression of GERD are controversial: some reports of increased esophageal acid exposure (EAE) and mucosal damage were considered as evidence for a stable disease course, while others interprete these findings as disease progression. The aim of this study is to analyze a large patient-population with persisting symptoms indicative of GERD under protonpumpinhibitor-therapy and identify components characterizing disease severity and progression. METHODS: Patients with symptoms indicative of GERD were included in the study in a tertiary referral center (Frankfurt, Germany). All selected patients were under long-term protonpumpinhibitor-therapy with persistant symptoms. All patients underwent investigations to collect data on their physical status, EAE, severity of esophagitis, anatomical changes, and esophageal functional defects as well as their relation to the duration of the disease. Incidence over time was plotted as survival curves and tested with Log-rank tests for the four main disease markers. Multivariate modeling with COX-regression model was used to estimate the general impact of the four main disease markers on the time course of the disease. In order to elucidate possible causal relationships over time, a path analysis (structural equation model) was calculated. RESULTS: From the database with 1480 data sets, 972 patients were evaluated (542 males, 430 females). The mean age was 50.5 years (range18-89). The mean body mass index was 27.2(19-48). The mean time between the onset of symptoms and the diagnostic investigations was 8.2 years (1-50). A longer disease history for GERD was significantly associated with a higher risk for LES-incompetence. The mean duration from symptom onset to the time of clinical investigation was 9 years for patients with LES-incompetence (n = 563), compared to a mean of 6 years for those with mechanically intact LES (n = 95). A longer period from symptom onset to diagnostics was significantly associated with higher acid exposure. The pathway analysis was significant for the following model: 'history' (P < 0.001➔LES-incompetence & Hiatal Hernia➔(p < 0,001)➔pH-score (P < 0.001).Conclusion: LES-incompetence, the functional deterioration of the LES, and the anatomical alteration at the esophagogastric junction (Hiatal Hernia) as well as an increased EAE were associated with a long history of suffering from GERD. Path modeling suggests a causal sequence overtime of the main disease-parameters, tentatively allowing for a prediction of the course of the disease.

[Guidelines of the German Respiratory Society for Diagnosis and Treatment of Adults Suffering from Acute, Subacute and Chronic Cough]. / Leitlinie der Deutschen Gesellschaft für Pneumologie und Beatmungsmedizin zur Diagnostik und Therapie von erwachsenen Patienten mit Husten.

The present 2019 S2k consensus guideline of the German Respiratory Society was written - in contrast to the predecessor more general S3 guidelines from 2004 and 2010 - for pneumologists, since 2014 the German College of General Practitioners and Family Physicians (DEGAM) published his own cough guidelines.The guideline contains 48 recommendations agreed by consensus and 16 statements, which are explained in the background text in the following nine chapters: epidemiology, physiology, classification, acute, subacute or chronic cough, diagnostics and therapy; an extra chapter was dedicated to chronic idiopathic cough. Further emphasis of the guideline is the physiology of cough in anticipation of the introduction of new drugs, as well as detailed treatises on cough triggered by affections in the upper respiratory tract or by gastroesophageal reflux. The guideline should provide the pneumologist with the latest knowledge from neighboring disciplines required for diagnosis and therapy of cough. The clinical chapters also contain a short summary, practical recommendations and a bibliography of their own. Three new, simplified algorithms for acute, subacute and chronic cough round off the Diagnostics chapter.

The 2018 ISDE achalasia guidelines.

Achalasia is a relatively rare primary motor esophageal disorder, characterized by absence of relaxations of the lower esophageal sphincter and of peristalsis along the esophageal body. As a result, patients typically present with dysphagia, regurgitation and occasionally chest pain, pulmonary complication and malnutrition. New diagnostic methodologies and therapeutic techniques have been recently added to the armamentarium for treating achalasia. With the aim to offer clinicians and patients an up-to-date framework for making informed decisions on the management of this disease, the International Society for Diseases of the Esophagus Guidelines proposed and endorsed the Esophageal Achalasia Guidelines (I-GOAL). The guidelines were prepared according the Appraisal of Guidelines for Research and Evaluation (AGREE-REX) tool, accredited for guideline production by NICE UK. A systematic literature search was performed and the quality of evidence and the strength of recommendations were graded according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE). Given the relative rarity of this disease and the paucity of high-level evidence in the literature, this process was integrated with a three-step process of anonymous voting on each statement (DELPHI). Only statements with an approval rate >80% were accepted in the guidelines. Fifty-one experts from 11 countries and 3 representatives from patient support associations participated to the preparations of the guidelines. These guidelines deal specifically with the following achalasia issues: Diagnostic workup, Definition of the disease, Severity of presentation, Medical treatment, Botulinum Toxin injection, Pneumatic dilatation, POEM, Other endoscopic treatments, Laparoscopic myotomy, Definition of recurrence, Follow up and risk of cancer, Management of end stage achalasia, Treatment options for failure, Achalasia in children, Achalasia secondary to Chagas' disease.

Foregut symptoms, somatoform tendencies, and the selection of patients for antireflux surgery.

A large variety of foregut symptoms can occur in patients with gastroesophageal reflux disease (GERD), which can overlap with other disorders such as somatoform disorders and dyspepsia. Due to unclear diagnostic situations, these patients are often not adequately treated. The aim of this study was the evaluation of patients with foregut symptoms, referred for possible antireflux surgery, regarding their relationship with GERD and somatization tendencies based on control data from an unselected population. Symptom evaluation and somatization screening were initiated both in volunteers and in patients with foregut symptoms and GERD. Unselected volunteers from a village population were also evaluated by symptom analysis and for somatisation tendency. In addition, patients with foregut symptoms were diagnosed for GERD, and symptom analysis and psychodiagnostic evaluation were performed. There is no major significant difference in the symptom-spectrum in patients with foregut symptoms, whether they have a proven pathologic acid exposure from GERD or not. The probability for the risk of somatization was 5.6% in the unselected population of nonpatient volunteers (n = 267). In patients with foregut symptoms (n = 750), the probability for the presence of somatoform tendencies was approximately 20%, independent whether these patients had a documented GERD or a normal esophageal acid exposure, implicating further diagnostic work-up for the selection of patients for antireflux surgery. There is a remarkable symptom load and variety in patients with GERD, in patients with foregut symptoms, and in an unselected population of volunteers. There is no difference in the risk for somatization between patients with foregut symptoms and those with documented GERD. Therapeutic decision making especially prior to antireflux surgery requires an awareness of mental and emotional challenges.

Jackhammer esophagus: high-resolution manometry and therapeutic approach using peroral endoscopic myotomy (POEM).

We present the first report on peroral endoscopic myotomy (POEM) in the treatment of jackhammer esophagus. A 34-year-old female patient was newly diagnosed with a jackhammer esophagus. After failure of medical treatment, the patient underwent POEM procedure for myotomy of the spastic segment. Postoperatively, a mild emphysema and pneumothorax occurred that required drainage and antibiotic therapy until full recovery. Discharge was possible after 5 days. Six months later, she presented with recurrent but mild pain due to a remnant spastic segment proximal to the myotomy. Endoscopic balloon dilation was performed twice within 6 weeks with full symptomatic relief of pain and mild symptoms of dysphagia.

The potential and perspective of peroral endoscopic esophageal myotomy for achalasia.

The therapeutic spectrum of this disorder consists of medical therapy, endoscopic balloon dilatation, endoscopic Botox injection, open or laparoscopic cardia myotomy, and most recently transesophageal endoscopic myotomy (POEM peroral endoscopic myotomy). The most important requirement is a well-experienced team in interventional flexible endoscopy. The endoscopist as well as the assisting staff should have experience in advanced therapeutic endoscopic techniques and hemostasis to handle all necessary endoscopic instruments such as injection needles, needle knife, triangle knife, coagulation graspers, and endoscopic clip handling and closures. In addition, advanced surgical and especially laparoscopic skills and experience as well as surgical knowledge about esophageal disease must be available in case of conversion and/or consultation. Prior to this procedure, the patient undergoes a detailed diagnostic work-up to confirm the diagnosis of achalasia. The procedures are performed in general anesthesia. The patient is brought in a supine position, and the abdomen is free for inspection and palpation during the procedure. The myotomy can be performed in different locations around the esophageal circumference. In Europe, several centers with large experience in esophageal disease, laparoscopy, and especially advanced interventional endoscopy have started to introduce this POEM-technique in their clinical practice. Initial success and low complication rates are quite promising and show a great future perspective for this technique. In the USA, POEM is a procedure with a substantial increase in numbers performed in the past years with a low complication rate. The largest series are performed in Asia with a great clinical success. The perspective of POEM may be the lesser access trauma. Its potential can be also realized in Redo cases, where experienced centers have initial experience with POEM after POEM and POEM after LHMD.

NOTES in Europe: summary of the working group reports of the 2012 EURO-NOTES meeting.

The sixth EURO-NOTES workshop (4 - 6 October 2012, Prague, Czech Republic) focused on enabling intensive scientific dialogue and interaction between surgeons, gastroenterologists, and engineers/industry representatives and discussion of the state of the practice and development of natural orifice transluminal endoscopic surgery (NOTES) in Europe. In accordance with previous meetings, five working groups were formed. In 2012, emphasis was put on specific indications for NOTES and interventional endoscopy. Each group was assigned an important indication related to ongoing research in NOTES and interventional endoscopy: cholecystectomy and appendectomy, therapy of colorectal diseases, therapy of adenocarcinoma and neoplasia in the upper gastrointestinal tract, treating obesity, and new therapeutic approaches for achalasia. This review summarizes consensus statements of the working groups.

Euro-NOTES Status Paper: from the concept to clinical practice.

BACKGROUND: The concept of natural orifice transluminal endoscopic surgery (NOTES) consists of the reduction of access trauma by using a natural orifice access to the intra-abdominal cavity. This could possibly lead to less postoperative pain, quicker recovery from surgery, fewer postoperative complications, fewer wound infections, and fewer long-term problems such as hernias. The Euro-NOTES Foundation has organized yearly meetings to work on this concept to bring it safely into clinical practice. The aim of this Euro-NOTES status update is to assess the yearly scientific working group reports and provide an overview on the current clinical practice of NOTES procedures. METHODS: After the Euro-NOTES meeting 2011 in Frankfurt, Germany, an analysis was started regarding the most important topics of the European working groups. All prospectively documented information was gathered from Euro-NOTES and D-NOTES working groups from 2007 to 2011. The top five topics were analyzed. RESULTS: The statements of the working group activities demonstrate the growing information and changing insights. The most important selected topics were infection issue, peritoneal access, education and training, platforms and new technology, closure, suture, and anastomosis. The focus on research topics changed over time. The principle of hybrid access has overcome the technical and safety limitations of pure NOTES. Currently the following NOTES access routes are established for several indications: transvaginal access for cholecystectomy, appendectomy and colon resections; transesophageal access for myotomy; transgastric access for full-thickness small-tumor resections; and transanal/transcolonic access for rectal and colon resections. CONCLUSIONS: NOTES and hybrid NOTES techniques have emerged for all natural orifices and were introduced into clinical practice with a good safety record. There are different indications for different natural orifices. Each technique has been optimized for the purpose of finding a safe and realistic solution to perform the procedure according to the specific indication.

Guidelines of the German Respiratory Society for diagnosis and treatment of adults suffering from acute or chronic cough.

The first set of German guidelines for diagnosis and treatment of patients suffering from acute or chronic cough was published in 2004. Scientific developments over the past five years necessitate an update. The purpose of this document is to assist in ascertaining underlying causes and treating cough, in order to eliminate or minimize impairments of patients' health. The guidelines aim to introduce scientifically founded, evidence-based steps for the diagnosis and treatment of cough and optimize cost-effectiveness. Recommendations are assessed through the GRADE system (The Grades of Recommendation, Assessment, Development and Evaluation). Cough as a symptom is categorized as either acute (lasting up to 8 weeks) or chronic (lasting more than 8 weeks) and attributed to distinct diseases. For acute and chronic cough the diagnostic algorithms are updated; cost effectiveness is also taken into account. Additionally, the most frequent diagnostic errors are highlighted. Finally, available therapeutic options are discussed.

German Respiratory Society guidelines for diagnosis and treatment of adults suffering from acute, subacute and chronic cough.

The present 2019 S2k consensus guideline of the German Respiratory Society was written for pneumologists - in contrast to the more general predecessor's S3 guidelines from 2004 to 2010 -, since 2014 the German College of General Practitioners and Family Physicians (DEGAM) published their own cough guidelines. The guidelines contain 48 recommendations agreed upon the consensus and 16 statements, which are explained in the background text in the following nine chapters: epidemiology, physiology, classification, acute, subacute or chronic cough, diagnostics and therapy; an extra chapter was dedicated to chronic idiopathic/refractory cough. Further emphasis of the guidelines is the physiology of cough in anticipation of the introduction of new drugs, as well as detailed treatment for cough triggered by affectations of the upper respiratory tract or gastroesophageal reflux. The guideline should provide the pneumologist with the latest knowledge for neighboring disciplines required for diagnosis and therapy of cough. The clinical chapters also contain a short summary, practical recommendations and a bibliography of their own. Three new simplified algorithms for acute, subacute and chronic cough, round off the diagnostics chapter.

Endoscopic full-thickness plication for the treatment of gastroesophageal reflux disease using multiple Plicator implants: 12-month multicenter study results.

BACKGROUND: The full-thickness Plicator (Ethicon Endosurgery, Sommerville, NJ, USA) was developed for endoscopic treatment of gastroesophageal reflux disease (GERD). The goal is to restructure the antireflux barrier by delivering transmural pledgeted sutures through the gastric cardia. To date, studies using this device have involved the placement of a single suture to create the plication. The purpose of this study was to evaluate the 12-month safety and efficacy of this procedure using multiple implants to restructure the gastroesophageal (GE) junction. METHODS: A multicenter, prospective, open-label trial was conducted at four tertiary centers. Eligibility criteria included symptomatic GERD [GERD Health-Related Quality-of-Life (GERD-HRQL) questionnaire, off of medication], and pathologic reflux (abnormal 24-h pH) requiring daily proton pump inhibitor therapy. Patients with Barrett's epithelium, esophageal dysmotility, hiatal hernia > 3 cm, and esophagitis (grade III or greater) were excluded. All patients underwent endoscopic full-thickness plication with linear placement of at least two transmural pledgeted sutures in the anterior gastric cardia. RESULTS: Forty-one patients were treated. Twelve months post treatment, 74% of patients demonstrated improvement in GERD-HRQL scores by > or = 50%, with mean decrease of 17.6 points compared with baseline (7.8 vs. 25.4, p < 0.001). Using an intention-to-treat model, 63% of patients had symptomatic improvements of > or = 50%, with mean GERD-HRQL decrease of 15.0 (11.0 vs. 26.0, p < 0.001). The need for daily proton pump inhibitor (PPI) therapy was eliminated in 69% of patients at 12 months on a per-protocol basis, and 59% on an intention-to-treat basis. Adverse events included postprocedure abdominal pain (44%), shoulder pain (24%), and chest pain (17%). No long-term adverse events occurred. CONCLUSIONS: Endoscopic full-thickness plication using multiple Plicator implants can be used safely and effectively to improve GERD symptoms and reduce medication use.

[Natural orifices transluminal endoscopic surgery (NOTES) in Germany: summary of the working group reports of the "D-NOTES meeting 2009"]. / Endoskopisches Operieren über natürliche Körperöffnungen (NOTES) in Deutschland: Zusammenfassung der Arbeitsgruppensitzungen der "D-NOTES 2009"

The D-NOTES-group met in June 2009 for an evaluation of ongoing preclinical and clinical activities in natural orifice endoscopic surgery and the further coordination of research in Germany. Different working groups with various topics were formed. Consensus statements among various participants with different scientific and medical background were initiated. In summary, important topics were handled such as the correct handling of bacterial contamination and related complications, the question of the ideal entry point and a secure closure, interdisciplinary cooperation, and matters related to training and education. Furthermore, participants agreed on terminological basics. A to-do-list for medical engineering was formulated.

[Gallbladder duplication--laparoscopic cholecystectomy 17 years after open cholecystectomy]. / Doppelt angelegte Gallenblase--Laparoskopische Cholezystektomie 17 Jahre nach konventioneller Cholezystektomie.

INTRODUCTION: Duplication of the gallbladder is a rare congenital anomaly. An incidence of 2.5:10,000 has been published in autoptic studies. METHODS: We carried out an analysis of the published case reports of the last 30 years to examine those cases in which an accessory gallbladder was pre- or intraoperatively detected or missed and to evaluate the implications of the time of diagnosis of the duplication on the surgical therapy. RESULTS: 28 case reports were analysed. If the duplication of the gallbladder was recognised pre-operatively or during operation, both gallbladders could be removed via laparoscopy in 80 % of the cases. Missing the second gallbladder can lead to persisting symptoms, postoperative complications as well as a recrudescence of the cholecystolithiasis with following reoperation. If a reoperation for a missed second gallbladder was necessary, only 14.3 % of these operations could be performed via laparoscopy. CASE REPORT: We report the case of a missed gall-bladder duplication with an acute cholecystitis causing a reoperation 17 years after the initial operation. A laparoscopic cholecystectomy was possible even though the initial operation was performed through open surgery. CONCLUSION: If recognised in preoperative examinations or during surgery a laparoscopic cholecystectomy of both gallbladders is possible in the majority of cases with duplicated gallbladder.

[Natural orifice transluminal endoscopic surgery in future obesity treatment]. / NOTES als Zukunftsmodel für die Adipositaschirurgie.

The current trend in surgery to minimize access trauma will continue. As experience grows, minimally invasive surgical techniques are used increasingly in major surgical procedures to treat morbid obesity. Obese patients benefit most from its low morbidity for complications. As a result transluminal endoscopic surgery via natural orifices (NOTES) is obviously of great interest due to its potential in obesity surgery. In NOTES procedures, natural orifices such as the transgastric, transvaginal, transcolonic, and transvesical routes are used. Possible advantages are faster recovery, less pain, greater patient mobility, no hernias, and better cosmesis. Endoscopic intraluminal techniques and sleeve gastrectomy are procedures which can be best transferred into NOTES and associated techniques. Obesity surgery is an important element of gastrointestinal surgery today and has an important future role in our societies. Principles of minimal access surgery, as represented by NOTES, will be developed further and play a future role in medicine.

[Less reflux recurrence following Nissen fundoplication : results of laparoscopic antireflux surgery after 10 years]. / Weniger Refluxrezidive nach Nissen-Fundoplikation : 10-Jahres-Ergebnisse der laparoskopischen Antirefluxoperation.

BACKGROUND: Reflux recurrence is the most common long-term complication following fundoplication. Results for different techniques of laparoscopic antireflux surgery were retrospectively compared after 10 years. METHODS: From 1992 to 1997, the 120 patients studied had laparoscopic fundoplication with 'tailored' approaches: 88 Nissen, 22 anterior, and ten Toupet fundoplications. Follow-up of 87% of these patients included disease-related questions and the gastrointestinal quality of life index (GIQLI). RESULTS: Of the patients, 89% would select surgery again. Regurgitations after fundoplication were noted from 15% of patients after Nissen, 44% after anterior, and 10% after Toupet types (P=0.04). Twenty-eight percent were on acid suppression therapy. Proton pump inhibitors were used less frequently following Nissen fundoplication (P=0.01). The GIQLI score was 110+/-24 without significant differences for type of fundoplication. DISCUSSION: Overall results are satisfactory after 10 years of experience with fundoplication. Total fundoplication appears to control reflux better than partial fundoplication.

An atomic model of crystalline actin tubes: combining electron microscopy with X-ray crystallography.

The packing of the G-actin monomers within crystalline actin tubes was investigated at atomic detail. To achieve this, we have chosen an integrated structural approach which combines intermediate resolution electron microscopy based 3-D reconstruction and surface metal shadowing of crystalline actin tubes with atomic resolution X-ray data of the G-actin monomer. Distinct from the parallel, half-staggered packing of the actin subunits within F-actin filaments, the arrangement of actin monomers within the crystalline tubes involves antiparallel packing into dimers with p2 symmetry. Within the crystalline tubes, the actin monomers are oriented so that the filament axis runs parallel with the sheet plane and the intersubunit contacts in this direction are similar to those existing along the two long-pitch helical strands of the F-actin filament. The other intersubunit contacts within the crystalline tubes are not found in the actin filament. The ability of actin to form a variety of polymorphic oligomers is still not fully understood, and the functional implications of this variability have yet to be deciphered. Regularly packed actin assemblies such as sheets, tubes or ribbons may ultimately yield structural relationships to in vivo relevant actin oligomers such as, for example, the "lower dimer".

Surface topographies at subnanometer-resolution reveal asymmetry and sidedness of aquaporin-1.

Aquaporin-1 (AQP1) is an abundant protein in human erythrocyte membranes which functions as a specific and constitutively active water conducting pore. Solubilized and isolated as tetramer, it forms well-ordered two-dimensional (2D) crystals when reconstituted in the presence of lipids. Several high resolution projection maps of AQP1 have been determined, but information on its three-dimensional (3D) mass distribution is sparse. Here, we present surface reliefs at 0.9 nm resolution that were calculated from freeze-dried unidirectionally metal-shadowed AQP1 crystals as well as surface topographs recorded with the atomic force microscope of native crystals in buffer solution. Our results confirm the 3D map of negatively stained AQP1 crystals, which exhibited tetramers with four major protrusions on one side and a large central cavity on the other side of the membrane. Digestion of AQP1 crystals with carboxypeptidase Y, which cleaves off a 5 kDa intracellular C-terminal fragment, led to a reduction of the major protrusions, suggesting that the central cavity of the tetramer faces the outside of the cell. To interpret the results, sequence based structure predictions served as a guide.