eMedicine Specialties > Oncology > Carcinomas of the Gastrointestinal Tract

Carcinoid Tumor, Intestinal: Differential Diagnoses & Workup

Author: Hemant Singhal, MD, MBBS, FRCSE, FRCS(C), Senior Lecturer, Department of Surgery, Imperial College School of Medicine, UK; Consultant Surgeon, Northwick Park and St Marks Hospitals, UK
Coauthor(s): Kanchan Kaur, MBBS, MS, MRCS (Ed), Clinical Fellow, Department of Surgery, Northwick Park Hospital, UK; Alan A Saber, MD, MS, FACS, Chief, Minimally Invasive Surgery and Bariatric Surgery, Associate Professor, Department of Surgery, Michigan State University; Charles Zammit, MD, Senior Specialist Registrar, Department of Surgery, Breast Unit Charing Cross Hospital of London, England; Michael K McLeod, MD, FACE, FACS, Professor of Surgery and Program Director, Integrated General Surgery Program, Department of Surgery, Michigan State University College of Human Medicine
Contributor Information and Disclosures

Updated: Jan 8, 2009

Differential Diagnoses

Irritable Bowel Syndrome
Malignant Neoplasms of the Small Intestine
Mastocytosis, Systemic
Thyroid, Medullary Carcinoma

Workup

Laboratory Studies

  • Unfortunately, as already mentioned, most patients with carcinoid tumors present with metastatic disease. Only approximately 20% of patients are diagnosed with potentially resectable disease.8
  • Urinalysis  
    • In persons with carcinoid syndrome, levels of urinary 5-HIAA are usually greatly increased. This is because tryptophan metabolism is diverted from protein and nicotinic acid metabolism to serotonin, with consequent breakdown to 5-HIAA. A very high (usually >5 times normal values) level of urinary 5-HIAA in a 24-hour collection is diagnostic, provided that avocados, bananas, plums, walnuts, pineapples, tomatoes, eggplants (aubergines), and cough medicines are excluded from the diet for 24 hours before the collection is made.
    • In very rare cases, usually in bronchial carcinoids or gastric tumors (derived from the foregut), the tumor cells lack the aromatic amino acid decarboxylase enzyme, and hence the secretion of 5-HTP is increased. If this is the situation, then 5-HIAA urinary excretion would be normal. The diagnosis is confirmed by measuring total 5-hydroxyindole excretion. Such measurement includes 5-HTP, serotonin, and 5-HIAA.

Imaging Studies

  • Ultrasound  
    • Ultrasound has limited use, particularly in lesions smaller than 1 cm.
    • Endoscopic ultrasound is useful for detecting gastric, duodenal, and pancreatic  lesions; experience in this technique is mainly in detecting duodenal gastrinomas and is highly operator dependent.9 It is also used to detect anal lesions.
  • CT scan  
    • Noncontrast CT scan is the investigation of choice for carcinoid tumors because metastatic carcinoid tumors are usually extremely vascular; consequently, they tend to become isodense in the presence of contrast.8
    • CT scan can also detect mesenteric involvement with tumor in 50% of patients with metastatic disease.
  • MRI
    • In the past, availability and the speed of the procedure initially limited use of this investigation. Another dilemma was the difficulty in distinguishing between small (<2 cm) vascular intrahepatic lesions and benign hemangiomas.
    • With technical improvements, MRIs are increasingly being used as the supplemental abdominal investigation of choice.
  • Radionucleotide scans
    • Radionucleotides injected into the blood stream can bind to the neuroendocrine tumor cells and thus help localize the site of the tumor.
    • The scan used most commonly is the OctreoScan in which octreotide (an analogue of somatostatin) is labelled with a radioactive isotope and injected. Carcinoid tumors often have somatostatin receptors on their surface. The radio-labelled analogue (111 In-octreotide) therefore binds to the tumor cells. Radiography then allows the tumor to be visualized. This test is particularly useful when other routine modalities have failed to localize the site of the carcinoid. Another compound used less commonly is I131 MIBG.
  • PET scan
    • This modality utilizes the ability of certain tumors to take up radiolabeled tracers and thus be used to assess the function of different metabolic pathways specific to the tissue being scanned. It is useful in those instances in which scintigraphy with In111 octreotide has been inconclusive.
    • FDG (F18 labelled deoxyglucose) is the tracer that is useful in detecting less differentiated neuroendocrine tumors, as they have a higher metabolic rate.
    • Well-differentiated tumors have slower metabolic rates and therefore do not take up FDG as avidly. These tumors are better visualized on PET scans, which use the tracer C15 5-HTP.

Other Tests

Endoscopy: Gastric and anal carcinoid tumors can be evaluated by endoscopic techniques. Standard gastroscopy is of limited use except in patients with multiple gastric carcinoids.

Staging

There is no single system of classification and staging of carcinoid tumors. The various different ways of classifying these tumors are as follows: 

  • Based on site of origin
    • Lung
    • Gastrointestinal
  • World Health Organization (WHO) classification of carcinoids: The WHO now classifies these growths on the basis of their malignant potential into the following categories:
    • Neuroendocrine tumors (benign)
    • Neuroendocrine cancers (malignant), which  are further subclassified as follows:
      • Well differentiated (less aggressive)
      • Poorly differentiated (aggressive)
  • Based on spread
    • Localized - Limited to the organ of origin
    • Regional spread - Limited infiltration into surrounding tissues
    • Distant metastasis

More on Carcinoid Tumor, Intestinal

Overview: Carcinoid Tumor, Intestinal
Differential Diagnoses & Workup: Carcinoid Tumor, Intestinal
Treatment & Medication: Carcinoid Tumor, Intestinal
Follow-up: Carcinoid Tumor, Intestinal
Multimedia: Carcinoid Tumor, Intestinal
References
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Further Reading

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Keywords

intestinal carcinoid tumor, intestinal carcinoid tumour, gastroenteropancreatic neoplasm, GEP, GEP neoplasm, well-differentiated gastrointestinal neuroendocrine cancer, GI neuroendocrine tumor, neuroendocrine tumor, neuroendocrine tumour, argentaffinoma, carcinoid syndrome, small bowel malignancy, irritable bowel syndrome, IBS, idiopathic flushing, intestinal tumor, intestinal tumour, GI tumor, GI tumour, gastrointestinal tumor, gastrointestinal tumour, intestinal malignancy, appendectomy, cancer of the appendix, carcinoid tumor of the appendix, carcinoid tumor of the small intestine, distal small bowel malignancy

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Contributor Information and Disclosures

Author

Hemant Singhal, MD, MBBS, FRCSE, FRCS(C), Senior Lecturer, Department of Surgery, Imperial College School of Medicine, UK; Consultant Surgeon, Northwick Park and St Marks Hospitals, UK
Hemant Singhal, MD, MBBS, FRCSE, FRCS(C) is a member of the following medical societies: Royal College of Physicians and Surgeons of Canada and Royal College of Surgeons of Edinburgh
Disclosure: Nothing to disclose.

Coauthor(s)

Kanchan Kaur, MBBS, MS, MRCS (Ed), Clinical Fellow, Department of Surgery, Northwick Park Hospital, UK
Disclosure: Nothing to disclose.

Alan A Saber, MD, MS, FACS, Chief, Minimally Invasive Surgery and Bariatric Surgery, Associate Professor, Department of Surgery, Michigan State University
Alan A Saber, MD, MS, FACS is a member of the following medical societies: American College of Surgeons, American Society for Gastrointestinal Endoscopy, and American Society for Metabolic and Bariatric Surgery
Disclosure: Nothing to disclose.

Charles Zammit, MD, Senior Specialist Registrar, Department of Surgery, Breast Unit Charing Cross Hospital of London, England
Disclosure: Nothing to disclose.

Michael K McLeod, MD, FACE, FACS, Professor of Surgery and Program Director, Integrated General Surgery Program, Department of Surgery, Michigan State University College of Human Medicine
Michael K McLeod, MD, FACE, FACS is a member of the following medical societies: American Association of Clinical Endocrinologists, American Association of Endocrine Surgeons, American College of Surgeons, American Medical Association, Association for Academic Surgery, Central Surgical Association, International Association of Endocrine Surgeons, Michigan State Medical Society, Midwest Surgical Association, National Medical Association, Society of American Gastrointestinal and Endoscopic Surgeons, and Western Surgical Association
Disclosure: Nothing to disclose.

Medical Editor

Lodovico Balducci, MD, Professor of Oncology and Medicine, University of South Florida College of Medicine; Division Chief, Senior Adult Oncology Program, H Lee Moffitt Cancer Center and Research Institute
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Benjamin Movsas, MD, Vice-Chairman, Department of Radiation Oncology, Fox Chase Cancer Center
Benjamin Movsas, MD is a member of the following medical societies: American College of Radiology, American Radium Society, and American Society for Therapeutic Radiology and Oncology
Disclosure: Nothing to disclose.

CME Editor

Rajalaxmi McKenna, MD, FACP, Southwest Medical Consultants, SC, Department of Medicine, Good Samaritan Hospital, Advocate Health Systems
Rajalaxmi McKenna, MD, FACP is a member of the following medical societies: American Society of Clinical Oncology, American Society of Hematology, and International Society on Thrombosis and Haemostasis
Disclosure: Nothing to disclose.

Chief Editor

Jules E Harris, MD, Clinical Professor of Medicine, Division of Hematology/Medical Oncology, Department of Internal Medicine, University of Arizona College of Medicine at Tucson; Consulting Staff, Arizona Cancer Center
Jules E Harris, MD is a member of the following medical societies: American Association for Cancer Research, American Association for the Advancement of Science, American Association of Immunologists, American Society of Hematology, and Central Society for Clinical Research
Disclosure: GlobeImmune Salary Consulting; Amplimed Consulting fee Consulting; FibroGen Consulting fee Consulting

 
 
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