Rob & Smith's

Operative Surgery

Surgery of the Upper Gastrointestinal Tract

Fifth edition

Rob & Smith's

Operative Surgery

General Editors

David C. Carter MD, FRCS(Ed), FRCS(Gias) Regius Professor of Clinical Surgery, Royal Infirmary, Edinburgh, UK

R. C. G. Russell MS, FRCS Consultant Surgeon, Middlesex Hospital and Royal National Throat, Nose and Ear Hospital, London, UK

Other volumes available in the series

Cardiac Surgery 4th Edition Stuart W. Jamieson and Norman E. Shumway

The Ear 4th Edition John C. Ballantyne and Andrew Morrison

General Principles, Breast and Extracranial Endocrines 4th Edition Hugh Dudley and Walter J. Pories

Genitourinary Surgery 5th Edition Hugh N. Whitfield

Gynaecology and Obstetrics 4th Edition J. M. Monaghan

The Hand 4th Edition Rolfe Birch and Donal Brooks

Head and Neck 4th Edition lanA. McGregor and David J. Howard

Neurosurgery 4th Edition Lindsay Symon, David G. T. Thomas and Kemp Clark

Nose and Throat 4th Edition John C. Ballantyne and D. F. N. Harrison

Consulting Editor

Hugh Dudley CBE, ChM, FRCS(Ed), FRACS, FRCS Emeritus Professor, StMary's Hospital, London, UK

Art Editor

Gillian lee FMAA, HonFIMI, AMI, RMIP 15 Little Plucketts Way, Buckhurst Hill, Essex, UK

Ophthalmic Surgery 4th Edition Thomas A. Rice, Ronald G. Michels and Walter W. J. Stark

Orthopaedics 4th Edition George Bentley and Robert B. Greer Ill

Paediatric Surgery 4th Edition L. Spitz and H. Homewood Nixon

Plastic Surgery 4th Edition T. L. Barclay and Desmond A. Kernahan

Surgery of the Colon, Rectum and Anus 5th Edition L. P. Fielding and S.M. Goldberg

Thoracic Surgery 4th Edition The late J. W. Jackson and D. K. C. Cooper

Trauma Surgery 4th Edition Howard R. Champion, John V. Robbs and Donald D. Trunkey

Vascular Surgery 5th Edition C. W. Jamieson and J. S. T. Yao

Rob & Smith's

Operative Surgery

Surgery of the Upper Gastrointestinal Tract Fifth edition

Edited by

Glyn G. Jamieson FRACS, FACS Dorothy Mortlock Professor of Surgery, University of Adelaide, Department of Surgery, Royal Adelaide Hospital, Adelaide, Australia

Haile T. Debas MD M. Galante Distinguished Professor of Surgery and Dean of the School of Medicine, University of California, San Francisco, California, USA

~~I'll SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

© 1994 Springer Science+ Business Media Dordrecht

Originally published by Chapman & Hall in 1994 Softcover reprint of the hardcover 5th edition 1994

Typeset in 10/11 Garamond lTC by Genesis Typesetting, Laser Quay, Rochester, Kent

ISBN 978-0-412-53550-5 ISBN 978-1-4899-6621-6 (eBook) DOI 10.1007/978-1-4899-6621-6

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page.

The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

A catalogue record for this book is available from the British Library

Library of Congress Catalog Card Number: 94-070237

Contributors

I. Braghetto MD Associate Professor, University of Chile, Department of Surgery, University Hospital, Santos Dumont 999, Santiago, Chile

F.). Branicki DM, FRCS, FRACS Department of Surgery, Royal Brisbane Hospital, University of Queensland, Queensland 4072, Australia

R. Britten-Jones Department of Surgery, Royal Adelaide Hospital, Adelaide, South Australia 5000, Australia

G. F. Ruess MD, FRCS(Ed) Professor of Surgery, Minimal Invasive Chirurgie, Eberhard-Karls University, Schnarrenberg Clinic, D7400 Tiibingen, Germany

R. Buhl MD Department of Surgery, University of Heidelberg, lm Neuenheimer Feld 110, D-69120 Heidelberg, Germany

R. Bumm MD Senior Resident in Surgery, Department of Surgery, Technical University of Munich, W-8000 Munich 80, Germany

S. H. Carvajal MD Research Fellow, Department of Surgery, University of California, 513 Parnassus Avenue, S-320 San Francisco, California 94143-0104, USA

J. L. Chassin MD Chairman, Department of Surgery, The New York Hospital Medical Center of Queens, 56-45 Main Street, Flushing, New York 11355-5095, USA

W. G. Cheadle MD Assistant Professor of Surgery, Department of Surgery, University of Louisvillle School of Medicine, Louisville, Kentucky 40292, USA

S.C. S. Chung MD, FRCS(Ed), MRCP Reader in Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong

A.). Csendes MD, FACS Professor of Surgery, University of Chile, Department of Surgery, University Hospital, Santos Dumont 999, Santiago, Chile

H. T. Debas MD M. Galante Distinguished Professor of Surgery and Dean of the School of Medicine, University of California, 513 Parnassus Avenue, S-320 San Francisco, California 94143-0104, USA

T. R. DeMeester MD Professor and Chairman, Department of Surgery, University of Southern California School of Medicine, Los Angeles, California 90033-4612, USA

C. Deschamps MD Senior Associate Consultant, Section of General Thoracic Surgery, Mayo Clinic and Mayo Foundation, Rochester, Minnesota, USA

E. Deslandres MD Assistant Professor, Department of Medicine, University of Montreal, Division of Gastroenterology, H6tei-Dieu de Montreal, 3840 RueSt Urban, Montreal, Quebec, Canada H2W 1T8

P. G. Devitt FRACS, FRCS Senior Lecturer, Department of Surgery, Royal Adelaide Hospital, Adelaide, South Australia 5000, Australia

C. Doherty MD, FACS Assistant Professor, Department of Surgery, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA

F. Dubois Professor, CMC Pte de Choisy, 6 Place de Port-au-Prince, 75013 Paris, France

A. Duranceau MD Professor of Surgery, Department of Surgery, University of Montreal, Division ofThoracic Surgery, H6tei-Dieu de Montreal, 3840 RueSt Urban, Montreal, Quebec, Canada H2W 1T8

F. H. Ellis )r MD, PhD Clinical Professor of Surgery, Harvard Medical School, and Chief Emeritus, Division of Cardiothoracic Surgery, New England Deaconess Hospital, 110 Francis Street, Boston, Massachusetts 02215, USA

F. Fekete MD Professor of Surgery and Chief, Department of Digestive Surgery, University Paris VII, H6pital Beau jon, 100 Blvd du General Leclerc, Clichy, Paris 92118, France

D. Fromm MD Penharthy Professor and Chairman, Department of Surgery, Wayne State University and Surgeon-in-Chief, Detroit Medical Center, Detroit, Michigan, USA

D. Gavriliu MD Professor at UNEX-AZ SRL, Universitatea Romana de Stiinte si Arte, Bucharest, Romania

J. A. Hagen MD Esophageal Fellow, Department of Surgery, University of Southern California School of Medicine, Los Angeles, California 90033-4612, USA

C. Herfath MD Professor and Head, Department of Surgery, University of Heidelberg, lm Neuenheimer Feld 110, D-69120 Heidelberg, Germany

C. A. Hiebert MD, FACS Chairman Emeritus, Department of Surgery, Maine Medical Center, Portland, Maine, USA

A. H. Holscher MD Assistant Professor of Surgery, Department of Surgery, Technical University of Munich, W-8000 Munich 80, Germany

G. J. Huang MD, FRCS Professor of Thoracic Surgery, Cancer Institute and Hospital, Chinese Academy of Medical Sciences, PO Box 2258, Beijing 100021, People's Republic of China

0. Huber MD Department of Surgery, University of California, San Francisco, California 94143-0788, USA

G. G. Jamieson FRACS, FACS Dorothy Mortlock Professor of Surgery, University of Adelaide, Department of Surgery, Royal Adelaide Hospital, Adelaide, South Australia 5000, Australia

S. Johnson MD Esophageal Fellow, Department of Surgery, University of Southern California School of Medicine, Los Angeles, California 90033-4612, USA

G. W. Johnston MCh, FRCS Honorary Professor, Queen's University Belfast, and Consultant Surgeon, Royal Victoria Hospital, Belfast BT12 6BA, UK

J.-P. Kim MD, FACS Professor of Surgery, College of Medicine, Seoul National University Hospital, 28 Yungon-Dong Chongno-Gu, Seoul11 0-744, Korea

0. Korn MD Instructor of Surgery, University of Chile, Department of Surgery, University Hospital, Santos Dumont 999, Santiago, Chile

J. E. J. Krige FRCS, FCS(SA) Associate Professor, Department of Surgery, University of Cape Town, Observatory 7925, South Africa

Z. H. Krukowski PhD, FRCS(Ed) Consultant Surgeon, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, AB9 2ZB, UK

B. launois MD, FACS Professor, Digestive and Transplantation Surgery, Hopital Pontchaillou, Rue Henri Le Guilloux, 3500 Rennes, France

T. lerut MD, PhD, FACS Department of General Thoracic Surgery, Catholic University Leuven, U.Z. Gasthuisberg, 3000 Leuven, Belgium

A. K. C. Li MA, MD, FRCS, FRCS(Ed), FRACS, FACS Professor and Chairman, Department of Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong

l. Lundell MD, PhD Associate Professor of Surgery, Department of Surgery, Sahlgren's Hospital, University of Gothenburg, S-41345 Gothenburg, Sweden

G. J. Maddern PhD, MS, FRACS Jepson Professor of Surgery, Department of Surgery, University of Adelaide and Queen Elizabeth Hospital, Woodville, South Australia 5011, Australia

J. W. Maher MD Section of Gastrointestinal Surgery, Department of Surgery, University of Iowa Hospitals and Clinics and College of Medicine, Iowa City, Iowa 52242, USA

M.A. Malias MD Resident Surgeon, Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA

A. Mannell FRACS, FRCS, MS Specialist Surgeon, The Rosebank Clinic, and Consultant Surgeon, Baragwanath Hospital, University of the Witwatersrand, johannesburg, South Africa

M. T. Marrinan FRCS(Ed) Fellow in Thoracic Surgery, Mayo Graduate School of Medicine, Rochester, Minnesota, USA

C. J. Martin FRACS Professor of Surgery, University of Sydney and Head of Surgical Division, Nepean Hospital, PO Box 63, Penrith, NSW 2751, Australia

E. E. Mason MD, PhD, FACS Professor Emeritus of Surgery, Department of Surgery, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA

N. A. Matheson ChM, FRCS, FRCS(Ed) Consultant Surgeon, Aberdeen Royal Infirmary, Foresterhill, Aberdeen AB92ZB, UK

H. Matthews FRCS Consultant Thoracic Surgeon, Regional Department of Thoracic Surgery, East Birmingham Hospital, Birmingham and Professor of Surgery, Department of Biological Sciences, University of Warwick, UK

J. E. Meilahn MD Assistant Professor of Surgery, Department of Surgery, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA

R. 0. Mitchell MD Resident Surgeon, Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA

M. W. Mulholland MD Associate Professor of Surgery, University of Michigan, 2920 Taubman Health Center, 1500 E, Medical Center Drive, Ann Arbor, Michigan 481 09-0331, USA

S. J. Mulvihill MD Associate Professor of Surgery, Department of Surgery, University of California, 533 Parnassus Avenue, U-122 San Francisco, California 94143-0788, USA

l. K. Nathanson FRACS Senior Lecturer, Department of Surgery, Clinical Sciences Building, University of Queensland, Royal Brisbane Hospital, Herston 4029, Queensland, Australia

P. E. O'Brien MD, FRACS Professor of Surgery, Monash University, Alfred Hospital, Prahtan, Melbourne, Victoria 3181, Australia

l. C. Olbe MD, PhD Associate Professor of Surgery, Department of Surgery, University of Gothenburg, Sahlgren's Hospital, 41345 Gothenburg, Swwden

M. J. Orloff MD Professor of Surgery, School of Medicine, University of California, San Diego, California 921 03, USA

M. S. Orloff MD Assistant Professor of Surgery, University of Rochester School of Medicine and Dentistry, Strong Memorial Hospital, 601 Elmwood Avenue, Rochester, New York 14642, USA

M. Orringer MD Professor and Head, Section of Thoracic Surgery, University of Michigan, 2120 Taubman Health Center, Ann Arbor, Michigan, 48109-0010, USA

Y. Panis MD Department of Digestive Surgery, University Paris VII, Hopital Beau jon, 100 Blvd du General Leclerc, Clichy, Paris 92118, France

W. S. Payne MD Emeritus Consultant, Section of General Thoracic Surgery, Mayo Clinic, Rochester, Minnesota S5905, USA

C. A. Pellegrini MD, FACS Ben A. Reid Sr Professor and Chairman, Department of Surgery, University of Washington, Seattle, Washington 98195, USA

H. C. Polk MD Senior Professor and Chairman, Department of Surgery, University of louisville School of Medicine, louisville, Kentucky 40292, USA

S. C. Rakic MD, PhD, FACS Department of Surgery, leyenburg Hospital, Postbus 40551, The Hague 2504 lN, The Netherlands

W. P. Ritchie Jr MD, PhD Professor and Chairman, Department of Surgery, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA

A. Sali PhD, FRACS, FACS Clinical Associate Professor of Surgery, University of Melbourne, Parkville, Victoria, Australia 3081

J. R. Siewert MD, FACS Professor of Surgery, Chairman of the Department of Surgery, Technical University of Munich, W-8000 Munich 80, Germany

A. E. Siperstein MD Department of Surgery, Mount Zion Medical Center of UCSF, San Francisco, California 94143-1610, USA

J. Terblanche ChM, FRCS, FCS(SA) Professor and Head, Department of Surgery, and Co-Director, MRC liver Research Centre, University of Cape Town, Observatory 7925, South Africa

V. F. Trastek MD, FACS Consultant, Section of General Thoracic Surgery, Mayo Clinic, Rochester, Minnesota 55905, USA

A. Watson MD, FRCS, FRCS(Ed), FRACS Consultant Surgeon, The Wellington Hospital, London NW8 9LE, UK

Contributing Medical Artists

Antoine Barnaud 11 Rue jacques Dulud, 92200 Neuilly sur Seine, France

Andrew Bezear 6 Queen Street, Godalming, Surrey GU7 1 BD, UK

Diane Bruyninckx MMAA, AIMI 20 Van Halmaelelei, B-2930 Brasschaat, Belgium

Angela Christie MMAA 14 West End Avenue, Pinner, Middlesex HAS 1 BJ, UK

Peter Cox RDD, MMAA, AIMI Canon Frome Court, Canon Frome, Ledbury, Herefordshire HR8 2TD, UK

Susan Darrington P.O. Box 581, Subiaco, Western Australia 6008

Raymond Evans BA(Hons), MMAA Unit of Art in Medicine, Department of Cell and Structural Biology, University of Manchester, Manchester M13 9PT, UK

Diane Kinton BA(Hons) Gillian Lee Illustrations, 15 Little Plucketts Way, Buckhurst Hill, Essex IG9 SQU, UK

Gillian lee FMAA, HonFIMI, AMI, RMIP Gillian Lee Illustrations, 15 Little Plucketts Way, Buckhurst Hill, Essex IG9 SQU, UK

Marks Creative Consultants 31 Waddon Road, Croydon, Surrey CRO 4LH, UK

Gillian Oliver MMAA, AIMI 15 Bramble Road, Hatfield, Hertfordshire AL 10 9RZ, UK

Paul Richardson BA(Hons) 54 Wellington Road, Orpington, Kent BRS 4AQ, UK

Denise Smith BA(Hons), MMAA Unit of Art in Medicine, Department of Cell and Structural Biology, University of Manchester, Manchester M13 9PT, UK

Contents

Instrumentation techniques

Preoperative and postoperative management

General operative techniques

Preface

Flexible endoscopy of the upper digestive tract A. Duranceau and E. Deslandres

Injection sclerotherapy of oesophageal varices J. E. J. Krige and J. Terblanche

Rigid oesophagoscopy M. T. Marrinan and C. Deschamps

Dilatation of oesophageal strictures A. 5ali

Preoperative and postoperative management of patients undergoing major upper gastrointestinal surgery G. G. Jamieson and H. T. Debas

Technique of cervical approach to the oesophagus T. Lerut

Abdominal-right thoracic approach to oesophagectomy 5. C. 5. Chung and A. K. C. Li

Left posterolateral thoracotomy H. Matthews

Left thoracoabdominal approach for exposure of the oesophagus A. Mannell

Abdominal incisions for approaching the abdominal oesophagus and stomach P. G. Devitt

Sutured oesophageal anastomosis A. Watson

Stapling techniques for anastomoses of the oesophagus G. G. Jamieson

Hand-sewn techniques for gastric anastomoses Z. H. Krukowski and N. A. Matheson

XV

1

10

21

26

39

45

52

56

61

70

79

84

88

Operations on the cervical oesophagus

Operations on the thoracic oesophagus: malignant conditions

Operations on the thoracic oesophagus: miscellaneous conditions

Stapling techniques for gastric anastomoses 108 j. L. Chassin

Small intestine as a replacement after oesophageal resection 120 P. G. Devitt

Use of colon as an oesophageal replacement 128 j. A. Hagen, S. johnson and T. R. DeMeester

Use of the stomach as an oesophageal substitute 142 A. H. Holscher and j. R. Siewert

Pouches as gastric substitutes 154 C. Herfath and K. Buhl

Extra-anatomical reconstruction of the resected oesophagus 165 A. Duranceau

Surgical anatomy of the cervical oesophagus G. G. jamieson

Cricopharyngeal myotomy and excision of a pharyngo­oesophageal diverticulum G. G. jamieson and A. Duranceau

Abdominal and right thoracic subtotal oesophagectomy B. Launois and G. j. Maddern

170

173

178

Left thoracic subtotal oesophagectomy 189 H. Matthews

Transhiatal oesophagectomy 196 M. B. Orringer

Eversion extraction oesophagectomy 211 G. G. jamieson

En bloc oesophagectomy for cancer of the distal oesophagus, cardia and proximal stomach 214 j. A. Hagen and T. R. DeMeester

Long oesophageal myotomy and excision of diverticula A. Duranceau

230

Extramucosal enucleation of leiomyoma of the oesophagus 237 G. j. Huang

Perforation of the oesophagus 244 C. A. Pellegrini and 0. Huber

Operations on the abdominal oesophagus

Operations for uncomplicated gastro-oesophageal reflux

Operations for complicated gastro-oesophageal reflux

Anatomy of the hiatus and abdominal oesophagus H. C. Polk jr, M.A. Malias and G. G. jamieson

256

Myotomy for achalasia: thoracic approach 262 F. H. Ellis jr

Myotomy for achalasia: abdominal approach 267 S.C. Rakfc

Paraoesophageal hiatus hernia 276 P. E. O'Brien

Oesophagogastrectomy for adenocarcinoma of the oesophagus and cardia 280 A. H. Holscher, R. Bumm and j. R. Siewert

Indications and preoperative assessment of patients for antireflux surgery G. G. jamieson

Abdominal fundoplication C. j. Martin

Anti reflux surgery by the thoracic approach C. A. Hiebert

Operations for uncomplicated gastro-oesophageal reflux: miscellaneous procedures P. G. Devitt and G. G. jamieson

Reoperative anti reflux surgery G. G. jamieson

292

294

301

307

316

Intrathoracic fundoplication 320 j. W. Maher

Combined Collis-Nissen operation 327 V. F. Trastek and W. S. Payne

Roux-en-Y diversion and fundoplication for gastro-oesophageal reflux 335 F. Fekete andY. Panis

Resection of oesophageal strictures R. 0. Mitchell, W. G. Cheadle and H. C. Polkjr

Operations for complicated gastro-oesophageal reflux: miscellaneous procedures G. G. jamieson

345

350

Vagotomy operations

Gastric drainage operations

Gastric resections

Operations for bleeding from the stomach and duodenum

Surgical anatomy of the vagus nerves H. T. Debas

354

Total abdominal vagotomy and drainage 360 H. T. Debas

Total (selective) gastric vagotomy 369 H. T. Debas

Proximal gastric vagotomy 373 H. T. Debas

Complications of ulcer surgery: prevention and reoperative management 382 H. T. Debas and 5. Carvajal

Pyloroplasty 5. J. Mulvihill

Gastroenterostomy H. T. Debas

Partial gastrectomy (and antrectomy) with a gastroduodenal anastomosis: Billroth I gastrectomy G. G. Jamieson and H. T. Debas

Partial gastrectomy with gastrojejunal anastomosis including

394

403

414

Roux-en-Y reconstruction 420 M. W. Mulholland

Abdominal total gastrectomy without radical lymph node dissection 436 L. Lundell and L. C. Olbe

Total gastrectomy with lymph node resection 450 J.-P. Kim

High lesser curve gastrectomy with oesophagojejunogastric reconstruction 465 A. Csendes, I. Braghetto and 0. Korn

Miscellaneous gastric resections 472 D. Fromm

Bleeding gastric or duodenal ulcer J. E. Meilahn and W. P. Ritchie Jr

Bleeding oesophageal and gastric varices: shunts M. J. Orloff and M. 5. Orloff

476

493

Miscellaneous conditions

Laparoscopic surgery

Bleeding oesophageal and gastric varices: stapling procedures 516 G. W. Johnston

Bleeding: three miscellaneous conditions 525 G. G. Jamieson

High gastrostomy with peritoneal cuff D. Gavriliu

Perforated peptic ulcer F.]. Branicki

Surgical management of duodenal diverticula H. T. Debas and S. H. Carvajal

Gastric operations in obesity surgery E. E. Mason and C. Doherty

General techniques in abdominallaparoscopic surgery A. E. Siperstein

527

530

537

548

561

Laparoscopic Nissen fundoplication 571 G. G. jamieson and R. Britten-Jones

Laparoscopic gastroenterostomy 575 L. K. Nathanson

Laparoscopic vagotomies 584 F. Dubois

Achalasia of the oesophagus: management by videoendoscopic ~~ry 5~ C. A. Pellegrini

Endoscopic oesophagectomy 601 G. Buess and G.]. Maddern

List of products 607

Index 609

Preface

In his preface to the previous edition of this volume, Hugh Dudley commented that 'although gastrointestinal surgery is an old established discipline, it continues to move forward'. Gastrointestinal surgery does indeed continue to move forward, and even the contributors to the last volume (which was published in 1983) would have been surprised at the rapid changes which were about to take place in gastrointestinal surgery. One of the changes, which amounts to a paradigm shift, is thoracoscopic and laparoscopic surgery. Another of the changes which was well established in 1983, but which has gathered momentum in the intervening years, is the separation of general surgery into subspecialties. This edition, for the first time, acknowledges these changes, and this volume is concerned with the upper gastroin­testinal tract alone and includes laparoscopic and thoracoscopic techniques.

As with previous editions we have asked experts to describe how they undertake procedures in their field of expertise. The emphasis is always on the practical, with the aim being that a competent surgeon, without great familiarity in an area, in appropriate circumstances would be able to carry out the procedure being described.

Hugh Dudley finished his preface with: 'Here then is how to do it in the gastrointestinal tract by those who know how to do it (with the possible exception, of course, of the editor's own contributions!)' We can think of no better way to finish, but will circumvent Hugh's modesty by paraphrasing his remark to: 'This volume is how to do it in the upper gastrointestinal tract by those who should know how to do it!'

Glyn G. Jamieson Haile T. De bas February 1994