Diagnostic Approach to a Suspected Small Bowel Neuroendocrine Tumor

👉Patients with small bowel carcinoids often present with a mesenteric mass without an imageable small bowel primary tumor.

  • The differential diagnosis of an isolated mesenteric tumor includes:
    • Lymphoma
    • Desmoid tumor
    • Reactive lymphadenopathy:
      • From an inflammatory process
    • Mesenteric peritoneal implant:
      • From an abdominal malignancy
    • Small bowel carcinoid
  • Desmoid tumors:
    • Often have a spiculated appearance on CT
  • In carcinoid tumors with associated mesenteric masses:
    • The relationship to the major mesenteric vessels should be assessed:
      • As nodal carcinoid metastases:
        • Can be unresectable:
          • If they involve the root of the mesentery
  • Patients with mesenteric masses should undergo:
    • Biochemical testing for carcinoid:
      • Serum chromogranin A
      • Urine 5-hydroxyindoleacetic acid [5-HIAA])
    • Endoscopy:
      • If the small bowel associated with the mesenteric mass is endoscopically accessible
    • Small bowel enterography (CT or MRI):
      • Can occasionally identify a previously occult primary small bowel tumor

Chromogranin A

  • Chromogranins are peptides:
    • Released from neuroendocrine cells:
      • Vary day to day and with food intake
  • Depending on the threshold used:
    • The sensitivity approaches 95%
    • The specificity is low (55%):
      • Given the high rate of false positivity:
        • As it is elevated in multiple other conditions, including:
          • Endocrine diseases
          • Inflammatory conditions
          • Proton pump inhibitor use

5-HIAA

  • 5-hydroxyindoleacetic acid (5-HIAA):
    • Is the end product of serotonin metabolism:
      • It is excreted in the urine
  • Twenty-four-hour urinary excretion of 5-HIAA:
    • Can be elevated:
      • In patients with carcinoid tumors
    • It is most useful in patients:
      • With carcinoid syndrome:
        • Where it has high (90%) sensitivity and specificity
    • In patients with carcinoid tumors:
      • Without carcinoid syndrome:
        • The sensitivity is lower (~ 70%) even when using a low-level 5-HIAA cutoff
  • Foods containing high levels of tryptophan or serotonin and certain drugs:
    • Can result in false positive values

CT

  • Small bowel carcinoid tumors:
    • Are often small (less than 2 cm median size):
      • And are thus difficult to identify by cross-sectional imaging
  • Given the hypervascularity of these tumors:
    • Arterial phase:
      • May improve visibility
  • More commonly:
    • CT imaging reveals:
      • Mesenteric or hepatic metastases:
        • Without a small bowel mass
  • The classic CT appearance demonstrates:
    • A “spokes in a wheel” pattern:
      • With a mesenteric nodal mass (wheel)
      • With radiating desmoplastic fibrosis
    • The occult primary small bowel carcinoid tumor:
      • Is often in the bowel adjacent to the nodal metastases:
        • And may manifest with radiographic signs of:
          • A partial small bowel obstruction
  • Enterography (CT or MR):
    • May have higher sensitivity in detection small bowel carcinoids:
      • But is not universally available and is understudied
    • CT imaging:
      • Often underestimates the extent:
        • Of mesenteric, peritoneal, and hepatic metastases

OctreoScan

  • Indium-111 pentetreotide (OctreoScan):
    • Exploits the presence of:
      • Somatostatin receptors on carcinoid tumor cells:
        • Unlike high-grade neuroendocrine:
          • Low-grade carcinoid tumors:
            • Express:
              • High levels of somatostatin receptors
  • Octreotide scans:
    • Can allow for metastatic assessment and can predict response to somatostatin analogue therapy
      • However:
        • The spatial resolution and sensitivity of small carcinoid tumor detection:
          • Is limited
  • Functional PET/CT (i.e., gallium-68 dotatate) scans:
    • Offer improved sensitivity and resolution:
      • And are preferred where available

ENDOSCOPY

  • Similar to small bowel adenocarcinomas:
    • Small bowel carcinoids must be in an endoscopically accessible location to be visualized by endoscopy
    • Because they are often in the distal most 60 cm of the terminal ileum:
      • Colonoscopy or retrograde enteroscopy:
        • Can often reach these tumors
  • Endoscopic assessment allows opportunities to:
    • Biopsy and tattoo the lesion for identification during resection

#Arrangoiz #SurgicalOncologist #CancerSurgeon #Teacher #Surgeon #SmallBowelTumors #Carcinoids

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