下部消化管疾患は結腸、直腸、肛門に影響を与え、機能性疾患（IBSは世界人口の約10〜15%に影響）から生命を脅かす悪性腫瘍（大腸癌は世界で3番目に多いがんで、年間190万件の新症例）まで多岐にわたります。大腸内視鏡検査は下部GI診断と治療の礎石であり、直接観察、生検、ポリープ除去（ポリペクトミー、EMR、ESD）、クローン病狭窄に対するバルーン拡張を含む治療的介入を可能にします。本ガイドは、BSG、ESGE、ECCOガイドラインに沿った主要な下部GI疾患、大腸内視鏡処置、管理戦略を網羅しています。
Overview of Lower GI Diseases
The lower gastrointestinal tract comprises the small intestine (jejunum and ileum), the large intestine (colon), the rectum, and the anus. Diseases affecting this region range from common functional disorders like irritable bowel syndrome (IBS) to serious conditions including colorectal cancer, inflammatory bowel disease (IBD), and diverticular disease.
Colonoscopy — a flexible camera examination of the entire colon — is the gold-standard diagnostic and therapeutic tool for lower GI disease. It allows direct visualisation of the colonic mucosa, biopsy of suspicious lesions, and removal of polyps before they become cancerous.
When to see a doctor
Rectal bleeding, persistent change in bowel habits, unexplained weight loss, abdominal pain lasting more than a few weeks, or anaemia without obvious cause should all prompt prompt medical evaluation.
Lower GI pathology encompasses neoplastic, inflammatory, functional, vascular, and structural disease. Risk stratification tools — including the FIT (faecal immunochemical test), NICE DG30 guidelines, and Manchester scoring — guide appropriate investigation pathways. Colonoscopy remains the definitive tool; however, CT colonography (virtual colonoscopy) is an accepted alternative in patients unfit for or declining optical colonoscopy. Capsule colonoscopy and AI-assisted adenoma detection are emerging adjuncts.
| Condition | Category | Key Investigation | Colonoscopy Role |
|---|---|---|---|
| Colorectal Cancer | Neoplastic | Colonoscopy + biopsy, CT staging, CEA | Diagnosis, tattooing, palliative stenting |
| Colorectal Polyps | Pre-neoplastic | Colonoscopy | Polypectomy (snare, EMR, ESD) |
| Crohn's Disease | Inflammatory (IBD) | Colonoscopy + ileoscopy, MRE, CRP, calprotectin | Diagnosis, surveillance, stricture dilation |
| Ulcerative Colitis | Inflammatory (IBD) | Colonoscopy + biopsy, calprotectin, CRP | Diagnosis, dysplasia surveillance |
| Diverticular Disease | Structural | CT abdomen, colonoscopy (elective) | Diagnosis, haemostasis for bleeding |
| IBS | Functional | Clinical (Rome IV criteria); exclusion of organic disease | Exclusion of IBD / malignancy |
Anatomy of the Lower GI Tract
Small Intestine
6–7 metres long; divided into duodenum, jejunum, and ileum. Primary site of nutrient absorption. Crohn's disease frequently affects the terminal ileum.
Colon (Large Intestine)
~1.5 metres long; divided into ascending, transverse, descending, and sigmoid segments. Absorbs water and electrolytes; forms and stores faeces. Most colorectal cancers arise here.
Rectum
The final 15 cm of the large bowel before the anus. Stores faeces before defecation. Rectal cancer has distinct treatment pathways from colon cancer, including neoadjuvant chemoradiotherapy.
Caecum & Appendix
The caecum is the junction between small and large intestine. The appendix is a small pouch arising from the caecum; appendicitis is one of the most common surgical emergencies.
Clinical Note — Colonoscopic Landmarks
Complete colonoscopy is defined by caecal intubation, confirmed by visualisation of the appendiceal orifice and ileocaecal valve, ideally supplemented by photodocumentation. The hepatic and splenic flexures are technically demanding; right-sided colon (ascending + caecum) harbours a disproportionate share of interval cancers — often flat or sessile serrated lesions missed on inadequate withdrawal. Withdrawal time ≥6 minutes is strongly correlated with adenoma detection rate (ADR). The ADR benchmark is ≥25% (≥20% in women, ≥30% in men) per BSG / ESGE quality standards.
Colorectal Cancer (CRC)
Colorectal cancer (CRC) is cancer of the colon or rectum. It is the third most common cancer worldwide and the second leading cause of cancer-related death. The good news is that it is one of the most preventable and treatable cancers when caught early — which is why screening programmes are so important.
Most colorectal cancers develop slowly over many years from benign growths called polyps. Regular colonoscopy screening allows these polyps to be detected and removed before they become cancerous — effectively preventing the disease from developing.
CRC staging follows the TNM system (UICC/AJCC 8th edition) and is complemented by the Dukes classification. MSI (microsatellite instability) and KRAS/NRAS/BRAF mutational status are mandatory for metastatic CRC to guide immunotherapy and anti-EGFR therapy eligibility. Lynch syndrome (hereditary non-polyposis colorectal cancer) accounts for 3–5% of all CRC; universal MMR/MSI testing of all CRC specimens is recommended by ESGE and BSG.
Warning Signs
Symptoms to Watch For
- Rectal bleeding or blood in stool
- Persistent change in bowel habits (>3 weeks)
- Unexplained weight loss
- Abdominal pain or bloating
- Feeling of incomplete bowel emptying
- Iron-deficiency anaemia (fatigue, pallor)
Key Risk Factors
- Age over 50
- Family history of CRC or polyps
- Personal history of polyps or IBD
- Hereditary syndromes (Lynch, FAP)
- High-red-meat / processed-meat diet
- Obesity, physical inactivity, smoking, alcohol
| TNM Stage | Dukes | Description | 5-yr Survival |
|---|---|---|---|
| I | A | Confined to bowel wall (submucosa or muscularis propria) | ~90% |
| II | B | Through bowel wall, no node involvement | ~75% |
| III | C | Regional lymph node involvement | ~50% |
| IV | D | Distant metastases (liver, lung, peritoneum) | ~14% |
Colorectal Polyps
Colorectal polyps are small growths on the inner lining of the colon or rectum. Most are harmless, but certain types — particularly adenomatous polyps — can slowly become cancerous over 10–15 years if left untreated. Removing them during colonoscopy (polypectomy) is one of the most effective cancer-prevention strategies available.
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Tubular Adenoma
Most common; low-grade dysplasia; low cancer risk if small
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Villous Adenoma
Higher malignant potential; often sessile and larger
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Sessile Serrated Lesion
Flat, right-sided; responsible for many interval cancers; easily missed
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Hyperplastic Polyp
Generally benign; no surveillance required if small and distal
Post-Polypectomy Surveillance — BSG 2020 Guidelines
| Risk Category | Finding | Surveillance Interval |
|---|---|---|
| Low | 1–2 adenomas <10 mm, low-grade dysplasia | No surveillance; return to population screening |
| Intermediate | 3–4 small adenomas, or 1–2 adenomas ≥10 mm | 3 years |
| High | ≥5 adenomas, or ≥1 adenoma ≥20 mm, or any HGD | 1 year |
| Serrated | SSL ≥10 mm or with dysplasia; ≥3 SSLs | 3 years |
Inflammatory Bowel Disease (IBD)
Inflammatory bowel disease (IBD) is a term for two chronic conditions that cause inflammation of the digestive tract: Crohn's disease and ulcerative colitis (UC). IBD is a lifelong condition that follows a relapsing-remitting course. While there is currently no cure, effective treatments can control symptoms and achieve long-term remission.
Crohn's Disease
- Can affect any part of the GI tract (mouth to anus)
- Transmural inflammation; skip lesions; cobblestone appearance
- Symptoms: diarrhoea, abdominal cramps, weight loss, fatigue
- Complications: strictures, fistulae, abscesses, perianal disease
- Endoscopic balloon dilation used for short fibrostenotic strictures
Ulcerative Colitis
- Confined to the colon and rectum; always involves the rectum
- Mucosal inflammation only; continuous involvement
- Symptoms: bloody diarrhoea, urgency, tenesmus, cramping
- Complications: toxic megacolon, fulminant colitis, dysplasia / CRC
- CRC surveillance colonoscopy from 8–10 years after diagnosis
IBD Therapy Ladder & Biologics
| Step | Drugs | Indication |
|---|---|---|
| 1st line | 5-ASA (mesalazine) — UC; corticosteroids (induction) | Mild-moderate UC; induction of remission |
| 2nd line | Azathioprine, 6-MP, methotrexate | Steroid-dependent / chronic active disease |
| 3rd line | Anti-TNF (infliximab, adalimumab), vedolizumab, ustekinumab, JAK inhibitors | Moderate-severe IBD refractory to immunomodulators |
| Surgery | Colectomy (UC), resection / strictureplasty (Crohn's) | Medically refractory disease, complications, dysplasia, CRC |
Diverticular Disease
Diverticula are small pouches that bulge outward through weak spots in the colon wall. Having these pouches — diverticulosis — is very common and usually causes no problems. Diverticulitis occurs when one or more of the pouches becomes inflamed or infected, causing pain and other symptoms.
Diverticulosis
Presence of diverticula without inflammation. Affects >50% of people over 70. Often asymptomatic — discovered incidentally during colonoscopy.
Acute Diverticulitis
Inflammation / infection of diverticula. Left iliac fossa pain, fever, altered bowel habit. CT abdomen is the diagnostic standard. Treated with antibiotics ± surgery for complications.
Diverticular Bleeding
Most common cause of significant lower GI bleeding in the elderly. Usually painless, right-sided, and self-limiting. Colonoscopy + haemostasis (clip, thermal) for persistent bleeding.
Prevention & Management
Irritable Bowel Syndrome (IBS)
IBS is a common functional bowel disorder characterised by abdominal pain associated with altered bowel habits (diarrhoea, constipation, or both) in the absence of structural or biochemical abnormalities. It affects up to 10–15% of the global population and significantly impairs quality of life.
IBS is a diagnosis of exclusion — meaning other serious conditions must be ruled out first. Colonoscopy may be recommended to exclude IBD, microscopic colitis, or colorectal cancer, particularly in patients with alarm features (rectal bleeding, weight loss, age >45 at onset, family history of CRC).
IBS is diagnosed using Rome IV criteria: recurrent abdominal pain ≥1 day/week for the last 3 months, associated with ≥2 of: related to defecation; associated with change in stool frequency; associated with change in stool form. Subtypes: IBS-D (diarrhoea-predominant), IBS-C (constipation-predominant), IBS-M (mixed), IBS-U (unsubtyped). Investigation: FBC, CRP, tTG-IgA (coeliac serology), faecal calprotectin (<50 µg/g has high NPV for IBD). Colonoscopy indicated if FCP elevated or alarm features present.
Dietary Management
- • Low-FODMAP diet (first-line dietary intervention)
- • Regular meal timing; avoid large meals
- • Reduce caffeine, alcohol, and carbonated drinks
- • Soluble fibre for IBS-C; avoid insoluble fibre in IBS-D
- • Probiotics: limited but emerging evidence
Pharmacological Options
- • Antispasmodics (mebeverine, hyoscine) — abdominal cramps
- • Loperamide — IBS-D symptom control
- • Laxatives (macrogol) — IBS-C
- • Low-dose tricyclic antidepressants — pain modulation
- • Linaclotide / plecanatide — IBS-C (NICE-approved)
大腸内視鏡検査・診断：ポリペクトミー、EMR、ESD・バルーン拡張
Colonoscopy is the most thorough way to examine the entire colon. A thin flexible tube with a camera and light is guided through the rectum and colon while the patient is under mild sedation. Polyps found during the procedure can often be removed immediately. The preparation involves bowel cleansing the day before with a laxative solution.
Optical Colonoscopy
Gold standard; diagnostic and therapeutic in the same session
CT Colonography
Non-invasive alternative; no biopsy capability; detects polyps ≥6 mm
FIT / Stool Testing
Non-invasive screening; positive result triggers colonoscopy referral
Endoscopic Resection Techniques
| Technique | Indication | Key Points |
|---|---|---|
| Cold snare polypectomy | Polyps <10 mm (especially <5 mm) | No electrocautery; lower bleeding risk; preferred for SSLs |
| Hot snare polypectomy | Pedunculated polyps 10–20 mm | Electrocautery; risk of delayed bleeding; clip prophylaxis for large stalks |
| EMR (Endoscopic Mucosal Resection) | Sessile lesions 10–20 mm | Submucosal injection lifts lesion; piecemeal if large; surveillance at 3–6 months |
| ESD (Endoscopic Submucosal Dissection) | >20 mm lesions requiring en-bloc resection | Technically demanding; longer procedure; lower recurrence vs piecemeal EMR |
| Balloon Dilation | Crohn's strictures of the colon / ileocolonic anastomosis | Short (<5 cm), fibrostenotic strictures; through-the-scope balloon; fluoroscopy optional |
Clinical Insights & Current Guidelines
BSG / ESGE 2023–2024 Key Updates
- • ESGE 2022 Quality Colonoscopy guideline: ADR ≥25% is a mandatory performance indicator; ADR <15% is a patient safety concern requiring retraining.
- • Bowel preparation: split-dose or day-of preparation is superior to previous day-only; BSG 2022 endorses low-volume preparations (1L + ascorbic acid) as equivalent to 2L or 4L high-volume preparations.
- • AI-assisted colonoscopy (CADe systems): ESGE recommends CADe systems as adjuncts to improve ADR, particularly for right-sided flat lesions. Not yet a substitute for technique.
- • Lynch syndrome: universal MMR testing of all new CRC diagnoses now recommended (BSG/ACPGBI 2020); colonoscopic surveillance every 1–2 years from age 25.
- • Crohn's stricture dilation: short (<5 cm), non-prestenotic, fibrostenotic ileocolonic strictures are suitable for through-the-scope balloon dilation; success rate ~85% at 12 months.
Balloon Dilation in Lower GI Disease
Endoscopic balloon dilation of colonic and ileocolonic strictures in Crohn's disease is a well-established technique that delays or avoids surgery in selected patients. The Amara 3-Stage Balloon Dilator provides progressive, controlled radial force across three sequential stages within a single catheter, reducing the need for multiple device exchanges and allowing the endoscopist to titrate dilation precisely. For anastomotic strictures post-colonic resection, stepwise dilation (typically 15→18→20 mm) minimises perforation risk. High-pressure balloons are required for fibrotic post-inflammatory strictures. Injection of long-acting corticosteroid (triamcinolone) at the stricture margin at time of dilation reduces recurrence in refractory cases.
Single-Use Endoscopes in Lower GI Endoscopy
The lower GI endoscopy landscape is seeing increasing adoption of single-use flexible sigmoidoscopes and colonoscopes, driven by infection control requirements (particularly post-COVID-19), reducing reprocessing burden, and improving access in outpatient and remote settings. Single-use devices eliminate the risk of transmission of prions, biofilm-forming organisms, and emerging pathogens (e.g. CRE) that have been linked to reusable endoscope channels despite high-level disinfection. Envaste's single-use scope portfolio supports this transition.
よくある質問：下部消化管疾患
大腸癌の警告サインは？
大腸癌の警告サインには、直腸出血または血便、3週間以上持続する排便習慣の変化、原因不明の体重減少、腹痛または腹部膨満感、不完全な排便感、鉄欠乏性貧血が含まれます。これらの症状は速やかな医療的評価が必要です。大腸癌は早期発見時に高度に治療可能であり、ステージIでの5年生存率は90%を超えます。
クローン病と潰瘍性大腸炎の違いは何か？
両者とも炎症性腸疾患（IBD）の形態です。クローン病は口から肛門までGI管のどこにでも影響し、全層性（全壁厚）炎症を引き起こし、飛び石病変、狭窄、瘻孔を伴う場合があります。潰瘍性大腸炎は結腸と直腸に限局し、常に直腸から始まる連続性の粘膜炎症を引き起こし、血性下痢、尿意切迫感、テネスムスを呈します。生検を伴う大腸内視鏡検査は診断と鑑別に不可欠です。
癌スクリーニングのための大腸内視鏡検査の頻度は？
平均リスクの個人に対して、大腸内視鏡検査スクリーニングは通常45〜50歳から推奨されます（各国ガイドラインによって異なります）。ポリープが発見されない場合、次の大腸内視鏡検査は10年後に推奨されます。腺腫性ポリープを有する個人はより早期のサーベイランスが必要です（大きさと数に応じて1〜3年）。大腸癌の家族歴、リンチ症候群、FAP、長期IBDを有する方は、より若い年齢から、より高頻度のスクリーニングが必要な場合があります。
大腸内視鏡検査とは何か、処置中に何が行われるか？
大腸内視鏡検査は、細い軟性カメラ（大腸内視鏡）を直腸から挿入して結腸全体を観察します。軽い鎮静下で行われます。前日に下剤溶液による腸管前処置で結腸を空にします。処置中、内視鏡医は結腸粘膜を観察し、生検を採取し、ポリペクトミーにより即座にポリープを除去します。処置は20〜45分かかります。CT大腸内視鏡検査（仮想大腸内視鏡検査）は、光学的大腸内視鏡検査を受けることができない患者への非侵襲的代替手段です。
バルーン拡張はIBD狭窄を手術なしに治療できるか？
はい—内視鏡的バルーン拡張術は、クローン病における短い（5cm未満）線維性回盲部および吻合部狭窄に対して確立された治療法です。バルーンカテーテルを大腸内視鏡から挿入し、拡張して狭窄部を徐々に拡げます。12ヶ月での成功率は約85%に達します。選択された患者では手術を回避または延期します。線維性狭窄には高圧バルーンが使用され、難治性症例では拡張時のステロイド注射が再発を低減します。