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Neuroendocrine tumours of GIT for md pathology exam

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carcinoid tumour GIT neuroendocrine histology microscopy

Histology image: Light microscopy of a formalin-fixed paraffin-embedded tissue section stained with Hematoxylin and Eosin reveals features consistent with an atypical carcinoid tumor, a pulmonary neuroendocrine neoplasm. Tumor cells are arranged in nests and sheets with occasional trabecular patterns, showing organoid architecture typical of neuroendocrine neoplasms. The cells are round to polygonal with moderate cytoplasm and nuclei displaying mild to moderate pleomorphism; chromatin may show a salt-and-pepper appearance. Notable features include focal necrosis and an elevated mitotic rate, defined here as 2–10 or more mitoses per high-power field, which supports the atypical designation over typical carcinoid. Calcifications can be present as small basophilic foci within tumor nests. The overall pattern is relatively cohesive with limited invasion into the surrounding stroma in this field. These histologic characteristics—neuroendocrine differentiation, organoid nesting, increased mitotic activity, and necrosis—confer clinical significance by indicating at least an intermediate-grade tumor with higher potential for metastasis compared to typical carcinoid. Clinically, this information informs prognosis and guides management decisions, including consideration of surgical resection and assessment for adjuvant therapy based on stage and grade. Differential diagnosis includes typical carcinoid, small cell lung carcinoma, and large cell neuroendocrine carcinoma within the pulmonary neuroendocrine tumor spectrum.

Histology image: Light microscopy of a formalin-fixed paraffin-embedded tissue section stained with Hematoxylin and Eosin reveals features consistent with an atypical carcinoid tumor, a pulmonary neuroendocrine neoplasm. Tumor cells are arranged in nests and sheets with occasional trabecular patterns, showing organoid architecture typical of neuroendocrine neoplasms. The cells are round to polygonal with moderate cytoplasm and nuclei displaying mild to moderate pleomorphism; chromatin may show a salt-and-pepper appearance. Notable features include focal necrosis and an elevated mitotic rate, defined here as 2–10 or more mitoses per high-power field, which supports the atypical designation over typical carcinoid. Calcifications can be present as small basophilic foci within tumor nests. The overall pattern is relatively cohesive with limited invasion into the surrounding stroma in this field. These histologic characteristics—neuroendocrine differentiation, organoid nesting, increased mitotic activity, and necrosis—confer clinical significance by indicating at least an intermediate-grade tumor with higher potential for metastasis compared to typical carcinoid. Clinically, this information informs prognosis and guides management decisions, including consideration of surgical resection and assessment for adjuvant therapy based on stage and grade. Differential diagnosis includes typical carcinoid, small cell lung carcinoma, and large cell neuroendocrine carcinoma within the pulmonary neuroendocrine tumor spectrum.

Imaging modality and technique: light microscopy of an H&E stained histology section. The specimen represents a carcinoid tumor, a well differentiated neuroendocrine neoplasm, captured in cross sections that reveal multiple growth patterns. The tumor nests, trabecular bands, rosette arrangements, and papillary or pseudoglandular formations predominate, with occasional solid areas and peripheral spindle cell arrangements typical of peripheral neuroendocrine tumors. The cells are uniform with round to oval nuclei, stippled 'salt and pepper' chromatin, and modest eosinophilic cytoplasm; mitotic activity is variable but generally low in well differentiated lesions. The background stroma is highly vascular and may show hyalinization, calcification, and in some cases mucin, amyloid, bone, or cartilage formation, reflecting the diverse morphologic spectrum of carcinoids. Immunophenotype is typically neuroendocrine, with positivity for chromogranin A and synaptophysin in well differentiated lesions; Ki-67 proliferation index correlates with grade. Clinically, recognition of the architectural heterogeneity is important, as carcinoid tumors may mimic other neoplasms on limited samples. The described pattern diversity informs differential diagnosis, guides immunohistochemical workup, and supports diagnosis of a neuroendocrine tumor. This image is educational for pathology learners, highlighting classic patterns of growth and the characteristic stromal background that aid in distinguishing carcinoid/neuroendocrine tumors from adenocarcinomas and poorly differentiated neoplasms.

Imaging modality and technique: light microscopy of an H&E stained histology section. The specimen represents a carcinoid tumor, a well differentiated neuroendocrine neoplasm, captured in cross sections that reveal multiple growth patterns. The tumor nests, trabecular bands, rosette arrangements, and papillary or pseudoglandular formations predominate, with occasional solid areas and peripheral spindle cell arrangements typical of peripheral neuroendocrine tumors. The cells are uniform with round to oval nuclei, stippled 'salt and pepper' chromatin, and modest eosinophilic cytoplasm; mitotic activity is variable but generally low in well differentiated lesions. The background stroma is highly vascular and may show hyalinization, calcification, and in some cases mucin, amyloid, bone, or cartilage formation, reflecting the diverse morphologic spectrum of carcinoids. Immunophenotype is typically neuroendocrine, with positivity for chromogranin A and synaptophysin in well differentiated lesions; Ki-67 proliferation index correlates with grade. Clinically, recognition of the architectural heterogeneity is important, as carcinoid tumors may mimic other neoplasms on limited samples. The described pattern diversity informs differential diagnosis, guides immunohistochemical workup, and supports diagnosis of a neuroendocrine tumor. This image is educational for pathology learners, highlighting classic patterns of growth and the characteristic stromal background that aid in distinguishing carcinoid/neuroendocrine tumors from adenocarcinomas and poorly differentiated neoplasms.

Imaging modality: light microscopy of an H&E stained histology slide of a carcinoid/neuroendocrine tumor. Primary subject: carcinoid tumor with trabecular architecture; other growth patterns such as nesting, rosettes, papillary or solid patterns are described in the literature, but the presented field most prominently demonstrates a classic trabecular arrangement of uniform, round to oval cells with salt-and-pepper chromatin and relatively scant cytoplasm. The tumor cells are arranged in interlacing cords and columns separated by delicate vascularized stroma, contributing to a highly vascular background. Mitotic activity is typically low in well-differentiated carcinoids, with mild cytologic atypia; necrosis is uncommon but may be present in larger tumors. Cytoplasm is amphophilic to eosinophilic; nuclei are round to elongated, with stippled chromatin. Rosettes or microcystic formations may be seen occasionally. The background stroma may show hyalinization, calcification, mucin, amyloid, bone or cartilage formation. Immunophenotype is typically positive for neuroendocrine markers such as synaptophysin and chromogranin A, supporting a neuroendocrine tumor diagnosis. Clinically, these lesions arise in the GI tract or bronchopulmonary system and may express diverse patterns; accurate histologic classification informs prognosis, surveillance, and therapeutic strategy, including surgical resection and consideration of adjuvant therapy in higher-grade cases. This aids in differential diagnosis and therapy planning.

Imaging modality: light microscopy of an H&E stained histology slide of a carcinoid/neuroendocrine tumor. Primary subject: carcinoid tumor with trabecular architecture; other growth patterns such as nesting, rosettes, papillary or solid patterns are described in the literature, but the presented field most prominently demonstrates a classic trabecular arrangement of uniform, round to oval cells with salt-and-pepper chromatin and relatively scant cytoplasm. The tumor cells are arranged in interlacing cords and columns separated by delicate vascularized stroma, contributing to a highly vascular background. Mitotic activity is typically low in well-differentiated carcinoids, with mild cytologic atypia; necrosis is uncommon but may be present in larger tumors. Cytoplasm is amphophilic to eosinophilic; nuclei are round to elongated, with stippled chromatin. Rosettes or microcystic formations may be seen occasionally. The background stroma may show hyalinization, calcification, mucin, amyloid, bone or cartilage formation. Immunophenotype is typically positive for neuroendocrine markers such as synaptophysin and chromogranin A, supporting a neuroendocrine tumor diagnosis. Clinically, these lesions arise in the GI tract or bronchopulmonary system and may express diverse patterns; accurate histologic classification informs prognosis, surveillance, and therapeutic strategy, including surgical resection and consideration of adjuvant therapy in higher-grade cases. This aids in differential diagnosis and therapy planning.

This histology image depicts a neuroendocrine carcinoma of the gastrointestinal tract, evaluated by light microscopy on a formalin-fixed paraffin-embedded tissue section stained with Hematoxylin and Eosin. The specimen is deep to the mucosa, in the submucosal compartment, consistent with an infiltrative neoplasm arising from the GI tract. At intermediate power, tumor cells are arranged in cohesive ribbons and trabeculae with cribriform-like infoldings and occasional nests within a fibrous stroma. The cells show increased nuclear-to-cytoplasmic ratio, hyperchromatic, grooved nuclei with irregular contours and conspicuous nucleoli; mitotic activity may be variable, with occasional apoptotic bodies; focal necrosis may be present in higher-grade lesions. The cytoplasm is scant to moderate, and a high-grade neuroendocrine carcinoma pattern is favored over a typical carcinoid. The architectural pattern, cohesive trabeculae, and back-to-back arrangement support a neuroendocrine phenotype; however, definitive classification requires immunohistochemistry (synaptophysin, chromogranin A, and Ki-67 proliferation index). Clinical correlation suggests a GI primary with regional/submucosal invasion; accurate grading (G1-G3) informs prognosis and chemo-sensitivity. Differential diagnoses include well-differentiated neuroendocrine tumor (carcinoid), small or large cell neuroendocrine carcinoma, and adenocarcinoma with neuroendocrine differentiation. This image is valuable for educational purposes, differential diagnosis discussions, and correlating histology with immunophenotype and clinical behavior.

This histology image depicts a neuroendocrine carcinoma of the gastrointestinal tract, evaluated by light microscopy on a formalin-fixed paraffin-embedded tissue section stained with Hematoxylin and Eosin. The specimen is deep to the mucosa, in the submucosal compartment, consistent with an infiltrative neoplasm arising from the GI tract. At intermediate power, tumor cells are arranged in cohesive ribbons and trabeculae with cribriform-like infoldings and occasional nests within a fibrous stroma. The cells show increased nuclear-to-cytoplasmic ratio, hyperchromatic, grooved nuclei with irregular contours and conspicuous nucleoli; mitotic activity may be variable, with occasional apoptotic bodies; focal necrosis may be present in higher-grade lesions. The cytoplasm is scant to moderate, and a high-grade neuroendocrine carcinoma pattern is favored over a typical carcinoid. The architectural pattern, cohesive trabeculae, and back-to-back arrangement support a neuroendocrine phenotype; however, definitive classification requires immunohistochemistry (synaptophysin, chromogranin A, and Ki-67 proliferation index). Clinical correlation suggests a GI primary with regional/submucosal invasion; accurate grading (G1-G3) informs prognosis and chemo-sensitivity. Differential diagnoses include well-differentiated neuroendocrine tumor (carcinoid), small or large cell neuroendocrine carcinoma, and adenocarcinoma with neuroendocrine differentiation. This image is valuable for educational purposes, differential diagnosis discussions, and correlating histology with immunophenotype and clinical behavior.

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I have all the key content I need. Let me now compile a comprehensive, exam-focused answer on GIT Neuroendocrine Tumours for MD Pathology.

Neuroendocrine Tumours of the GIT - MD Pathology

1. Introduction & Terminology

Neuroendocrine tumours (NETs) of the gastrointestinal tract were historically called carcinoid tumours - a term coined by Oberndorfer in 1907 to denote tumours that were "carcinoma-like" but apparently benign. The term "carcinoid" is now considered problematic because it implies indolent behavior and is used inconsistently. The WHO 2010/2017 classification uses "neuroendocrine tumour/neoplasm" (NET/NEN) as the preferred terminology, reserving "neuroendocrine carcinoma" (NEC) for poorly differentiated, high-grade neoplasms.
They arise from the diffuse neuroendocrine system (DNES) - previously known as the APUD cell system (Amine Precursor Uptake and Decarboxylation). The specific cells of origin in the GIT are the Kulchitsky cells (enterochromaffin cells) located at the base of intestinal crypts of Lieberkuhn.

2. Classification by Embryologic Origin (Williams & Sandler)

SegmentSitesSecretory ProductsCarcinoid Syndrome
ForegutStomach, proximal duodenum, lung, pancreasHistamine, catecholamines, 5-HTP (not 5-HT)Atypical: prolonged flushing, lacrimation, facial edema
MidgutDistal duodenum, jejunum, ileum, appendix, right colonSerotonin (5-HT) - produces in large quantityClassic carcinoid syndrome (when liver metastases present)
HindgutTransverse/descending/sigmoid colon, rectumUsually nonsecretoryRarely
Key facts:
  • Midgut carcinoids produce serotonin in great quantity, but it is released into the portal circulation and cleared by the liver - carcinoid syndrome only occurs if hepatic metastases are present (serotonin escapes hepatic filtration)
  • Foregut carcinoids produce 5-HTP because they lack the enzyme aromatic amino acid decarboxylase (AAAD) that converts 5-HTP to 5-HT
  • Hindgut tumours are most often nonsecretory

3. WHO Grading Classification (2017)

Based on Ki-67 labeling index and mitotic count - this is the most important prognostic parameter:
DifferentiationGradeKi-67 IndexMitoses per 10 HPF
Well differentiated (NET)G1≤3% (some sources ≤2%)<2
Well differentiated (NET)G23-20%2-20
Well differentiated (NET)G3>20%>20
Poorly differentiated (NEC)G3>20%>20
Important distinction: A G3 well-differentiated NET differs from a poorly differentiated NEC - both have Ki-67 >20% but differ in morphology, behavior, and treatment response. When Ki-67 and mitotic count give discordant grades, the higher grade is assigned (NANETS 2013 update).
Source: Yamada's Textbook of Gastroenterology, 7th ed.

4. Frequency and Location

  • Most common site: Appendix (most frequent GI site - approximately 50% of all GI NETs in older series), followed by ileum and rectum
  • Bailey & Love: "most commonly in the appendix, ileum and rectum in decreasing order of frequency"
  • Small bowel NETs: 1/3 are multiple
  • The appendiceal NET is usually benign if <2 cm; those >2 cm have significant risk of metastasis
  • Gastrinomas ("triangle of gastrinoma"): 90% within the gastrinoma triangle - bounded by cystic duct, junction of 2nd and 3rd parts of duodenum, and junction of head and neck of pancreas

5. Histopathology (MORPHOLOGY - High Yield)

Gross Appearance

  • Primary is usually small and firm
  • May cause dense desmoplastic fibrosis in surrounding mesentery - causing bowel kinking, obstruction, and a characteristic radiological "sunburst" mesenteric appearance
  • Cut surface: yellow-tan in color
  • Liver metastases can be bulky even with small primaries

Microscopic Appearance (H&E)

Well-differentiated NETs show a characteristic organoid architecture:
  • Nesting/insular pattern (most common)
  • Trabecular/ribbon-like pattern
  • Glandular/tubular/acinar pattern
  • Rosette (pseudorosette) formation
  • Mixed patterns common
Cytology: Uniform, small-to-medium sized cells with:
  • Round to oval nuclei
  • "Salt and pepper" chromatin (finely stippled - the hallmark feature)
  • Inconspicuous nucleoli
  • Moderate eosinophilic cytoplasm
  • Low mitotic activity (in G1)
  • Highly vascular stroma
Poorly differentiated NEC (G3):
  • Large or small cell neuroendocrine carcinoma morphology
  • High nuclear:cytoplasmic ratio
  • Prominent nucleoli
  • Frequent mitoses and necrosis
Here are the histological appearances:
H&E - Well-differentiated NET (insulinoma), showing organoid nesting pattern:
H&E histology of well-differentiated NET showing organoid nesting with uniform cells and salt-and-pepper chromatin
H&E - Carcinoid tumour showing classic trabecular and nesting growth patterns:
H&E carcinoid tumour with trabecular nesting pattern and uniform cells
Ki-67 immunostaining of a poorly differentiated NET (>20% positivity = G3):
Ki-67 immunostaining of neuroendocrine tumour showing brown nuclear positivity

6. Histochemical & Immunohistochemical Staining

Special Stains

StainReactionBasis
Fontana-Masson (argentaffin reaction)Positive (black/silver)Self-reduce silver - contains serotonin granules; midgut tumours
Grimelius (argyrophil reaction)PositiveRequires external reducing agent; more sensitive, foregut + midgut
Periodic acid-Schiff (PAS)VariableMucinous variants
  • Argentaffin +: midgut (serotonin-producing) carcinoids
  • Argyrophil +: all NETs (more sensitive)

Immunohistochemistry (IHC) - Neuroendocrine Markers

MarkerComment
SynaptophysinMost sensitive pan-neuroendocrine marker; stains all NETs
Chromogranin A (CgA)Most specific; also used as serum tumour marker
CD56 (NCAM)Additional neuroendocrine marker
NSE (Neuron-specific enolase)Less specific
Ki-67Grading marker (MIB-1 antibody)
Specific functional markers: Insulin, Gastrin, Glucagon, VIP, Somatostatin, Serotonin - identify the functional subtype.

7. Tumour Markers (Laboratory Diagnosis)

Serotonin Pathway

  • Most 5-HT produced by midgut carcinoids is taken up by platelets in the portal circulation and stored in their dense granules
  • A portion enters renal tubules → converted to 5-hydroxyindoleacetic acid (5-HIAA) by monoamine oxidase and aldehyde dehydrogenase
  • 24-hour urinary 5-HIAA is the standard screening test (normal <10 mg/day)
  • False positives: tryptophan-rich foods (avocado, banana, pineapple, walnuts, tomatoes), drugs (phenothiazines)
  • Platelet serotonin is the most accurate marker (not affected by diet)
  • 5-HIAA and 5-HT may be normal in 20-30% of patients, particularly foregut and hindgut tumours

Other Markers

MarkerUse
Chromogranin A (serum)Best overall tumour burden marker; correlates with treatment response
5-HIAA (24h urine)Serotonin-producing (midgut) NETs
GastrinGastrinoma / ZES
Insulin + C-peptideInsulinoma
VIPVIPoma
GlucagonGlucagonoma
PP (pancreatic polypeptide)Nonfunctioning PNETs
Source: Quick Compendium of Clinical Pathology, 5th ed.

8. Carcinoid Syndrome

Definition: Clinical syndrome resulting from systemic release of vasoactive substances, occurring almost exclusively with hepatic metastases (liver can no longer clear portal serotonin) or with bronchial/ovarian primary (drains directly to systemic circulation, bypassing portal system).

Classic Features (midgut serotonin-secreting tumours):

  • Episodic flushing (reddish-blue cyanosis) - triggered by alcohol, stress, food
  • Diarrhea (watery, secretory) with borborygmi
  • Bronchospasm (wheezing)
  • Right-sided heart disease: tricuspid regurgitation ± pulmonary stenosis (fibrous plaques - carcinoid heart disease; serotonin causes endocardial fibrosis on the right side because left side is protected by pulmonary metabolism of serotonin)
  • Pellagra-like skin changes (due to diversion of tryptophan to serotonin synthesis)
Atypical carcinoid syndrome (foregut - histamine + 5-HTP secreting):
  • Prolonged patchy flushing
  • Lacrimation, periorbital edema
  • Bronchoconstriction
  • No 5-HIAA elevation

Carcinoid Crisis

  • Life-threatening exacerbation of carcinoid syndrome
  • Triggered by: surgical manipulation, induction of anesthesia, tumor necrosis (from chemotherapy/embolization)
  • Prevention: Octreotide (somatostatin analogue) prophylaxis

9. Specific GIT NETs

A. Appendiceal NET (most common GI NET)

  • Arises from subepithelial enterochromaffin cells at the base of crypts
  • Most found incidentally during appendicectomy
  • Usually at the tip of the appendix
  • <2 cm: essentially benign, simple appendicectomy curative
  • >2 cm: significant risk of metastasis, right hemicolectomy required
  • Goblet cell carcinoid (adenocarcinoid): mixed neuroendocrine-mucin-secreting adenocarcinoma; more aggressive

B. Small Bowel NET (most common cause of carcinoid syndrome)

  • Most common in the terminal ileum
  • 1/3 are multiple (multicentric)
  • Cause intense desmoplastic reaction in mesentery
  • Most likely to cause carcinoid syndrome when metastatic
  • IHC: serotonin positive, chromogranin A+, synaptophysin+
  • Argentaffin positive

C. Gastric NET

Three types:
TypeAssociationBiology
Type I (75%)Chronic atrophic gastritis, hypergastrinemiaBenign, ECL cell origin
Type II (5-10%)MEN1 + ZES, hypergastrinemiaLow-grade malignant
Type III (15-20%)Sporadic, normal gastrinMost aggressive; may metastasize

D. Gastrinoma (Zollinger-Ellison Syndrome)

  • G-cell tumour secreting gastrin → massive HCl production
  • ZES triad: severe peptic ulcers (often multiple, atypical sites), diarrhea, elevated gastrin
  • 20-30% associated with MEN1 (look for multiple pancreatic tumours)
  • Up to 5% develop ectopic ACTH secretion (Cushing syndrome)
  • Gastrinoma triangle - 90% of gastrinomas occur here
  • Fasting serum gastrin >1000 pg/mL highly diagnostic; secretin stimulation test
  • Treated with: PPIs (for acid control), surgical resection (for cure), octreotide

E. Insulinoma

  • Most common functional PNET (60% of functional pancreatic NETs)
  • Whipple's triad: symptomatic hypoglycemia (symptoms with fasting/exercise) + blood glucose <2.5 mmol/L + relief with glucose
  • 4-6% associated with MEN1; 5% malignant (lowest malignancy rate of all PNETs)
  • Usually small (<2 cm), solitary, evenly distributed in head/body/tail
  • Diagnosis: elevated fasting insulin + C-peptide, low blood glucose

F. VIPoma (WDHA syndrome / Verner-Morrison syndrome / Pancreatic cholera)

  • Watery Diarrhea, Hypokalemia, Achlorhydria
  • Massive secretory diarrhea (>6-8 L/day), tea-coloured, persists with fasting
  • 80-90% in pancreas (often tail); 50-89% metastatic at presentation
  • VIP → stimulates adenylate cyclase in intestinal epithelium → massive Cl-/water secretion

G. Glucagonoma

  • Glucagon-secreting pancreatic NET; primarily >50 years
  • Classic presentation: 4Ds - Diabetes (mild), Dermatitis (necrolytic migratory erythema - pathognomonic), DVT/thrombosis, Depression
  • Necrolytic migratory erythema (NME): erythematous vesiculobullous rash on lower limbs, groin, perineum; due to glucagon excess and hypoaminoacidemia

H. Somatostatinoma

  • Rare; Inhibitory hormone → inhibits everything
  • Somatostatinoma triad: Diabetes mellitus (mild), Steatorrhea (fat malabsorption), Cholelithiasis (gallstones - reduced cholecystokinin effect)
  • Most found in pancreas head or duodenum
  • Duodenal somatostatinomas have association with von Recklinghausen's disease (NF1)

10. Genetics and Hereditary Associations

SyndromeGeneAssociated NETs
MEN1MEN1 (menin)Gastrinoma, insulinoma, VIPoma, glucagonoma (3 Ps: Parathyroid, Pituitary, Pancreas)
MEN2A/2BRETMedullary thyroid carcinoma, pheochromocytoma
VHLVHLPancreatic NETs (non-functional)
NF1NF1Duodenal somatostatinomas, carcinoids
TSCTSC1/TSC2Pancreatic NETs

11. Prognosis and Malignancy

  • All NETs are potentially malignant - the distinction benign vs malignant cannot be made on histology alone; only metastasis confirms malignancy
  • Appendiceal NETs <2 cm: very rarely malignant
  • Ileal NETs: frequently malignant despite small size
  • 5-year survival by grade: G1 ~95%, G2 ~75%, G3 (NEC) ~15-25%
  • Hepatic metastases: most common site; patients may live many years even with metastatic disease (slow growth rate)

12. Treatment Summary

ModalityApplication
SurgeryFirst-line for resectable disease; appendicectomy for appendiceal NETs <2 cm; right hemicolectomy for >2 cm
Octreotide / LanreotideSomatostatin analogues - control carcinoid syndrome (flushing, diarrhea); antiproliferative; must cover surgery/anaesthesia to prevent carcinoid crisis
Octreotide scanning (somatostatin receptor scintigraphy)Staging and detection of metastases; detects occult primaries
PRRT (Peptide receptor radionuclide therapy)177Lu-DOTATATE for somatostatin-receptor positive metastatic NETs
Hepatic resection / ablationPalliative cytoreduction for liver metastases
ChemotherapyLess effective for well-differentiated NETs; streptozocin + 5-FU for PNETs; platinum-based for poorly differentiated NEC

13. High-Yield Exam Points

  1. Cell of origin: Kulchitsky (enterochromaffin) cells at base of crypts of Lieberkuhn
  2. Most common site: Appendix; most common site causing carcinoid syndrome = terminal ileum
  3. Argentaffin vs Argyrophil: Argentaffin (self-reduces silver) = midgut only; Argyrophil = all NETs
  4. Carcinoid syndrome requires liver metastases (or bronchial primary) - portal serotonin cleared by liver
  5. 5-HIAA in urine = screening test; false positives with tryptophan-rich foods
  6. Chromogranin A = best serum marker for tumour burden
  7. IHC: Synaptophysin (most sensitive) + Chromogranin A (most specific)
  8. "Salt and pepper" chromatin = hallmark nuclear feature
  9. Carcinoid heart disease = RIGHT-sided (tricuspid regurgitation, pulmonary stenosis); left side protected by lung degradation of serotonin
  10. WHO grading based on Ki-67 and mitotic count - G1/G2/G3
  11. Gastrinoma triangle: cystic duct + D2/D3 junction + neck/head of pancreas = 90% of gastrinomas
  12. Glucagonoma 4Ds: Diabetes, Dermatitis (NME - pathognomonic), DVT, Depression
  13. VIPoma = WDHA (Watery Diarrhea, Hypokalemia, Achlorhydria)
  14. Somatostatinoma triad: Diabetes + Steatorrhea + Cholelithiasis
  15. MEN1: gastrinoma, insulinoma - 20-30% of gastrinomas are MEN1-associated
  16. Malignancy cannot be determined histologically - only by presence of metastasis
  17. Appendiceal NETs: <2 cm = benign behavior; >2 cm = need right hemicolectomy
Primary sources: Quick Compendium of Clinical Pathology 5th ed.; Yamada's Textbook of Gastroenterology 7th ed.; Bailey and Love's Short Practice of Surgery 28th ed.; Robbins Pathologic Basis of Disease; Sleisenger and Fordtran's GI & Liver Disease
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