CINXE.COM
Medical Encyclopedia: MedlinePlus
<!DOCTYPE html> <html lang="en" id="static-share" class="nojs us" data-root="https://medlineplus.gov/"> <head> <meta charset="utf-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" /> <meta http-equiv="window-target" content="_top" /> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <meta name="viewport" content="width=device-width, initial-scale=1" /> <link rel="canonical" href="https://medlineplus.gov/encyclopedia.html" /> <link rel="alternate" hreflang="en" href="https://medlineplus.gov/encyclopedia.html" /> <link rel="alternate" hreflang="es" href="https://medlineplus.gov/spanish/encyclopedia.html" /> <meta name="ac-dictionary" content="medlineplus-ac-dictionary" /> <meta property="og:image" content="https://medlineplus.gov/images/mplus_fb.jpg" /> <meta name="description" content="The A.D.A.M. Medical Encyclopedia includes articles about diseases, tests, symptoms, injuries, and surgeries. Search encyclopedia articles from A to Z." /> <meta name="NLMDC.Date.Expiration" content="2025-01-01"/> <link rel="shortcut icon" href="https://medlineplus.gov/images/favicon.ico" type="image/x-icon" /> <link rel="apple-touch-icon" href="https://medlineplus.gov/images/touch-icon.png" /> <meta property="fb:app_id" content="1042245625821448" /> <meta property="og:title" content="Medical Encyclopedia: MedlinePlus" /> <meta property="og:url" content="https://medlineplus.gov/encyclopedia.html" /> <title>Medical Encyclopedia: MedlinePlus</title> <link rel="stylesheet" href="https://medlineplus.gov/css/common_new.css?1721154787422" /> <!--[if IE 8]> <link rel="stylesheet" href="https://medlineplus.gov/css/ie8/common.css"> <![endif]--> <link rel="stylesheet" href="https://medlineplus.gov/uswds/css/uswds_styles.css" /> <link rel="stylesheet" href="https://medlineplus.gov/utilities/lostatic.css" id="lostatic" media="all"/> <!--[if IE 8]> <link href="https://medlineplus.gov/utilities/ie8lostatic.css" type="text/css" rel="stylesheet" media="all"/> <![endif]--> <script type="text/javascript">document.getElementsByTagName('html')[0].className = document.getElementsByTagName('html')[0].className.replace( /(?:^|\s)nojs(?!\S)/g , '').trim();</script> <script src="https://medlineplus.gov/uswds/js/uswds-init.min.js" type="text/javascript"></script> <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0], j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src= 'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); })(window,document,'script','dataLayer','GTM-MMVM77');</script> </head> <body> <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-MMVM77" height="0" width="0" style="display:none;visibility:hidden" title="googletagmanager"></iframe></noscript> <a name="top" id="top"></a> <a class="hide-offscreen" href="#start">Skip navigation</a> <section class="usa-banner" aria-label="Official website of the United States government" > <div class="usa-accordion"> <header class="usa-banner__header"> <div class="usa-banner__inner"> <div class="grid-col-auto"> <img aria-hidden="true" class="usa-banner__header-flag" src="https://medlineplus.gov/uswds/img/us_flag_small.png" alt="" /> </div> <div class="grid-col-fill tablet:grid-col-auto" aria-hidden="true"> <p class="usa-banner__header-text"> An official website of the United States government </p> <p class="usa-banner__header-action">Here鈥檚 how you know</p> </div> <button type="button" class="usa-accordion__button usa-banner__button" aria-expanded="false" aria-controls="gov-banner-default-default" > <span class="usa-banner__button-text">Here鈥檚 how you know</span> </button> </div> </header> <div class="usa-banner__content usa-accordion__content" id="gov-banner-default-default" > <div class="grid-row grid-gap-lg"> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="https://medlineplus.gov/uswds/img/icon-dot-gov.svg" role="img" alt="" aria-hidden="true" /> <div class="usa-media-block__body"> <p> <strong>Official websites use .gov</strong><br />A <strong>.gov</strong> website belongs to an official government organization in the United States. </p> </div> </div> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="https://medlineplus.gov/uswds/img/icon-https.svg" role="img" alt="" aria-hidden="true" /> <div class="usa-media-block__body"> <p> <strong>Secure .gov websites use HTTPS</strong><br />A <strong>lock</strong> ( <span class="icon-lock" ><svg xmlns="http://www.w3.org/2000/svg" width="52" height="64" viewBox="0 0 52 64" class="usa-banner__lock-image" role="img" aria-labelledby="banner-lock-description-default" focusable="false" > <title id="banner-lock-title-default">Lock</title> <desc id="banner-lock-description-default">Locked padlock icon</desc> <path fill="#000000" fill-rule="evenodd" d="M26 0c10.493 0 19 8.507 19 19v9h3a4 4 0 0 1 4 4v28a4 4 0 0 1-4 4H4a4 4 0 0 1-4-4V32a4 4 0 0 1 4-4h3v-9C7 8.507 15.507 0 26 0zm0 8c-5.979 0-10.843 4.77-10.996 10.712L15 19v9h22v-9c0-6.075-4.925-11-11-11z" /> </svg> </span >) or <strong>https://</strong> means you鈥檝e safely connected to the .gov website. Share sensitive information only on official, secure websites. </p> </div> </div> </div> </div> </div> </section> <div id="mplus-wrap"> <header> <div id="mplus-header"> <div id="mplus-orgs"> <a href="http://www.nih.gov/" class="nih-org" target="_blank" title="National Institutes of Health"> <img class="nihlogo" src="https://medlineplus.gov/images/nihlogo.png" alt="National Institutes of Health"/> </a><a href="https://www.nlm.nih.gov/" target="_blank"> National Library of Medicine</a> </div> <div id="mplus-logo" class="years-25"> <a href="https://medlineplus.gov/"> <img alt="MedlinePlus Trusted Health Information for You" title="MedlinePlus Trusted Health Information for You" src="https://medlineplus.gov/images/m_logo_25.png"/> </a> </div> <div id="mplus-nav"> <div aria-live="polite" class="sm-live-area hide-offscreen"></div> <button id="sm-menu-btn" class="navmenu-btn" title="Menu" role="button" aria-controls="mplus-menu-list" type="submit">Menu<span class="icon icon-nav-menu"></span></button> <ul id="mplus-menu-list" class="nav-list"> <li><a href="https://medlineplus.gov/healthtopics.html">Health Topics</a></li> <li><a href="https://medlineplus.gov/druginformation.html">Drugs & Supplements</a></li> <li><a href="https://medlineplus.gov/genetics/">Genetics</a></li> <li><a href="https://medlineplus.gov/lab-tests/">Medical Tests</a></li> <li><a href="https://medlineplus.gov/encyclopedia.html">Medical Encyclopedia</a></li> <li><a href="https://medlineplus.gov/about/">About MedlinePlus</a></li> </ul><button id="sm-search-btn" class="navmenu-btn" title="Search" role="button" aria-controls="mplus-search" type="submit"><span class="hide-offscreen"></span>Search<span class="icon icon-nav-search"></span></button> <div class="top-1"> <form id="mplus-search" method="get" action="https://vsearch.nlm.nih.gov/vivisimo/cgi-bin/query-meta" title="Search MedlinePlus" target="_self"> <input type="hidden" name="v:project" value="medlineplus"/> <input type="hidden" name="v:sources" value="medlineplus-bundle"/> <div class="form-box text-combo"> <div class="form-area"><label class="hide-offscreen" for="searchtext_primary">Search MedlinePlus</label> <input id="searchtext_primary" class="form-text" type="text" placeholder="Search MedlinePlus" alt="#Site Search input" title="Site Search input" maxlength="400" size="40" name="query" autocomplete="off" role="textbox" aria-autocomplete="list" aria-haspopup="true"/> </div> <div class="button-area"> <button class="form-btn" title="Search MedlinePlus" alt="Search MedlinePlus" type="submit">GO</button> </div> </div> </form> <div class="secondarynav"> <ul class="nav-list"> <li><a href="https://medlineplus.gov/about/"><span>About MedlinePlus</span></a></li> <li><a href="https://medlineplus.gov/whatsnew/">What's New</a></li> <li><a href="https://medlineplus.gov/sitemap.html"><span>Site Map</span></a></li> <li><a href="https://support.nlm.nih.gov/knowledgebase/category/?id=CAT-01231&category=medlineplus&from=https%3A//medlineplus.gov/encyclopedia.html" target="_blank"><span>Customer Support</span></a></li> </ul> </div> </div> <div id="mplus-nav-bar"> <ul class="nav-list"> <li><a href="https://medlineplus.gov/healthtopics.html">Health Topics</a></li><li><a href="https://medlineplus.gov/druginformation.html">Drugs & Supplements</a></li><li><a href="https://medlineplus.gov/genetics/">Genetics</a></li><li><a href="https://medlineplus.gov/lab-tests/">Medical Tests</a></li><li><a href="https://medlineplus.gov/encyclopedia.html">Medical Encyclopedia</a></li> </ul> </div> <a id="mplus-lang-toggle" href="https://medlineplus.gov/spanish/encyclopedia.html" title="Espa帽ol">Espa帽ol</a> </div> </div> </header> <div id="mplus-content"> <div id="static-page"> <!-- Breadcrumbs --> <div id="breadcrumbs"> <div itemprop="breadcrumb" itemscope="" itemtype="http://schema.org/BreadcrumbList"> <span class="hide-offscreen">You Are Here:</span> <div itemscope itemprop="itemListElement" itemtype="http://schema.org/ListItem"> <a href="https://medlineplus.gov/" itemprop="item"><span itemprop="name">Home</span></a> → <meta itemprop="position" content="1"/> </div> <div> <span>Medical Encyclopedia</span> </div> </div> </div> <span class="page-url print-only">URL of this page: https://medlineplus.gov/encyclopedia.html</span> <!-- Article --> <article> <!-- Two Column Layout--> <div class="page-info"> <div class="page-title"> <a name="start" id="start"></a> <h1>Medical Encyclopedia</h1> </div> <div class="page-actions"><!-- Share Buttons --></div> <noscript> <span class="js-disabled-message">To use the sharing features on this page, please enable JavaScript.</span> </noscript> </div> <div class="main"> <p>The A.D.A.M. Medical Encyclopedia includes over 4,000 articles about diseases, tests, symptoms, injuries, and surgeries. It also contains an extensive library of medical photographs and illustrations. For more information about A.D.A.M., see its <a target="TheNewWin" href="http://www.adam.com/editorialGuidelines.aspx">content review board</a>.</p> <nav role="navigation"> <div class="alphanav section azlanding"> <div class="section-header"> <div class="section-title"> <h2>Find encyclopedia articles A-Z</h2> </div> <div class="section-button"> <button type="submit" aria-controls="az-section2" role="button" title="Expand/Collapse section" aria-pressed="false" tabindex="0"> <span class="icon icon-section-action"></span> </button> </div> <!-- Area for accessibility for mobile --> <div class="sm-live-area hide-offscreen" aria-live="polite"></div> </div> <div class="section-body bluearea" id="az-section2"> <ul class="alpha-links"> <li><a href="ency/encyclopedia_A.htm">A</a></li> <li><a href="ency/encyclopedia_B.htm">B</a></li> <li><a href="ency/encyclopedia_C.htm">C</a></li> <li><a href="ency/encyclopedia_D.htm">D</a></li> <li><a href="ency/encyclopedia_E.htm">E</a></li> <li><a href="ency/encyclopedia_F.htm">F</a></li> <li><a href="ency/encyclopedia_G.htm">G</a></li> <li><a href="ency/encyclopedia_H.htm">H</a></li> <li><a href="ency/encyclopedia_I.htm">I</a></li> <li><a href="ency/encyclopedia_J.htm">J</a></li> <li><a href="ency/encyclopedia_K.htm">K</a></li> <li><a href="ency/encyclopedia_L.htm">L</a></li> <li><a href="ency/encyclopedia_M.htm">M</a></li> <li><a href="ency/encyclopedia_N.htm">N</a></li> <li><a href="ency/encyclopedia_O.htm">O</a></li> <li><a href="ency/encyclopedia_P.htm">P</a></li> <li><a href="ency/encyclopedia_Q.htm">Q</a></li> <li><a href="ency/encyclopedia_R.htm">R</a></li> <li><a href="ency/encyclopedia_S.htm">S</a></li> <li><a href="ency/encyclopedia_T.htm">T</a></li> <li><a href="ency/encyclopedia_U.htm">U</a></li> <li><a href="ency/encyclopedia_V.htm">V</a></li> <li><a href="ency/encyclopedia_W.htm">W</a></li> <li><a href="ency/encyclopedia_X.htm">X</a></li> <li><a href="ency/encyclopedia_Y.htm">Y</a></li> <li><a href="ency/encyclopedia_Z.htm">Z</a></li> <li><a href="ency/encyclopedia_0-9.htm">0-9</a></li> </ul> </div> </div> </nav> <div class="adam-logo"><a target="TheNewWin" href="https://www.adam.com/about"><img alt="About A.D.A.M." src="https://medlineplus.gov/images/ftrAdamlogo.gif"/></a></div> <p>The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 1997-2024 A.D.A.M., Inc. Duplication for commercial use must be authorized in writing by ADAM Health Solutions.</p> </div> </article> </div> </div> <footer> <div id="mplus-footer"> <div class="footer1"> <ul class="secondarynav"> <li><a href="https://medlineplus.gov/about/">About MedlinePlus</a></li> <li><a href="https://medlineplus.gov/whatsnew/">What's New</a></li> <li><a href="https://medlineplus.gov/sitemap.html">Site Map</a></li> <li><a href="https://support.nlm.nih.gov/knowledgebase/category/?id=CAT-01231&category=medlineplus&from=https%3A//medlineplus.gov/encyclopedia.html" target="_blank"><span>Customer Support</span></a></li> </ul> <ul class="follow-footer"> <li> <a href="https://medlineplus.gov/rss.html" class="follow-item">Subscribe to RSS<img src="https://medlineplus.gov/images/feed.png" class="social-media-toolkit-icon" alt="RSS" title="RSS"></a> </li> <li> <span class="follow-label">Follow us</span> <a href="https://twitter.com/medlineplus" class="follow-item" target="_blank"> <img src="https://medlineplus.gov/images/i_share_twitter.png" class="follow-icon" alt="X" title="X"> </a> <a href="https://facebook.com/Mplus.gov/" class="follow-item" target="_blank"> <img src="https://medlineplus.gov/images/i_share_fb.png" class="follow-icon" alt="Facebook" title="Facebook"> </a> <a href="https://www.instagram.com/mplusgov/" class="follow-item" target="_blank"> <img src="https://medlineplus.gov/images/Instagram_Glyph_Gradient_RGB.png" class="follow-icon" alt="Instagram" title="Instagram"> </a> </li> <li> <a href="https://medlineplus.gov/social-media-toolkit/" class="social-media-toolkit-item">Social Media Toolkit<img src="https://medlineplus.gov/images/i_social_media_toolkit.png" class="social-media-toolkit-icon" alt="Social Media Toolkit" title="Social Media Toolkit"></a> </li> </ul> </div> <div class="footer2"> <ul> <li><a href=" https://www.nlm.nih.gov/web_policies.html" target='_blank'>NLM Web Policies</a></li> <li><a href="https://medlineplus.gov/about/using/usingcontent/" >Copyright</a></li> <li><a href="https://medlineplus.gov/accessibility.html">Accessibility</a></li> <li><a href="https://medlineplus.gov/about/using/criteria/">Guidelines for Links</a></li> <li><a href="https://medlineplus.gov/plugins.html">Viewers & Players</a></li> <li><a href="https://www.hhs.gov/vulnerability-disclosure-policy/index.html" target="_blank">HHS Vulnerability Disclosure</a></li> <li><a href="https://medlineplus.gov/medlineplus-connect/">MedlinePlus Connect for EHRs</a></li> <li><a href="https://medlineplus.gov/about/developers/">For Developers</a></li> </ul> <div class="address"> <a href="https://www.nlm.nih.gov" target="_blank">National Library of Medicine</a> <span>8600 Rockville Pike, Bethesda, MD 20894</span> <a href="http://www.hhs.gov" target="_blank">U.S. Department of Health and Human Services</a> <a href="http://www.nih.gov" target="_blank">National Institutes of Health</a> </div> <div class="date"> </div> <div class="return-top"><a href="#top" title="Return to top"><img class="return-top-icon" alt="Return to top" src="https://medlineplus.gov/images/return-top.png"></a></div> </div> </div> </footer> </div> <script src="https://medlineplus.gov/jslib/jquery-3.6.0.min.js" type="text/javascript"></script> <script src="https://medlineplus.gov/jslib/mplus-frontend-controls-new.js" type="text/javascript"></script> <script src="https://medlineplus.gov/jslib/mplus-share.js?id=1112022" type="text/javascript"></script> <!--[if lte IE 9]><script src="//www.nlm.nih.gov/medlineplus/jslib/jquery.placeholder.js" type="text/javascript"></script><![endif]--> <script src="https://medlineplus.gov/jslib/control.js" type="text/javascript"></script> <script src="https://medlineplus.gov/uswds/js/uswds.min.js" type="text/javascript"></script> <script src="https://medlineplus.gov/utilities/lostatic.js" type="text/javascript"></script> </body> </html>