Appendiceal carcinoid tumor (neuroendocrine tumor — NET) is the most common primary neoplasm of the appendix, accounting for 50-85% of all appendiceal tumors. It originates from enterochromaffin cells and is typically located at the appendiceal tip. Most are <1 cm and detected incidentally in appendectomy specimens. CT shows a solid, homogeneously enhancing small intramural nodule.
Age Range
15-65
Peak Age
40
Gender
Female predominant
Prevalence
Uncommon
Appendiceal carcinoid tumors are well-differentiated neuroendocrine neoplasms originating from enterochromaffin (Kulchitsky) cells. These cells are located at the basal part of the appendiceal mucosa and produce neuroendocrine markers such as serotonin, chromogranin A, and synaptophysin. The tumor typically begins in the submucosa and may invade muscularis propria with slow growth. Their localization at the appendiceal tip is due to high enterochromaffin cell density in this region. Tumor size is the most important prognostic determinant: tumors <1 cm have <2% metastasis risk while tumors >2 cm have >30% metastasis risk. Solid enhancement on CT reflects the tumor's hypervascular nature because neuroendocrine tumors have a rich capillary network.
A markedly homogeneously enhancing, well-defined solid nodule at the appendiceal tip on arterial phase CT is the most characteristic finding of appendiceal carcinoid tumor. The triad of location (tip), enhancement pattern (hypervascular), and homogeneous structure strongly supports this diagnosis. Thin-section reconstructions and arterial phase images are critical for detecting tumors <1 cm.
A markedly enhancing solid nodule is seen at the appendiceal tip on arterial phase. Enhancement is homogeneous and intense, reflecting the tumor's hypervascular nature. The nodule typically measures 5-15 mm and enhances more intensely than the surrounding appendiceal wall.
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A markedly enhancing ... mm solid nodule at the appendiceal tip on arterial phase may be consistent with carcinoid tumor.
A well-defined, solid intramural mass is seen at the appendiceal tip on portal venous phase. Enhancement is homogeneous with no necrosis or calcification typically (in tumors <2 cm). The mass originates from the appendiceal wall and may partially obstruct the lumen.
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A ... mm well-defined solid intramural mass is identified at the appendiceal tip.
Secondary acute appendicitis findings may accompany due to carcinoid tumor causing luminal obstruction: proximal appendiceal dilatation, periappendiceal stranding, wall enhancement. In this situation, the primary tumor may be overlooked as a small nodule at the distal appendix.
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Solid nodule at the appendiceal tip accompanied by acute appendicitis findings is noted; carcinoid tumor should be considered as the cause of obstructive appendicitis.
On MRI, carcinoid tumor shows intermediate signal intensity on T2-weighted sequences. Isointense to mildly hyperintense on T1. Post-contrast sequences show marked homogeneous enhancement. Mild-to-moderate diffusion restriction may be seen on DWI.
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The lesion at the appendiceal tip shows intermediate T2 signal with marked post-contrast enhancement, consistent with neuroendocrine tumor.
On ultrasound, a hypoechoic, solid, well-defined nodule is seen at the appendiceal tip. The nodule is more hypoechoic than the surrounding appendiceal wall with homogeneous internal structure. Increased vascularity may be detected on color Doppler.
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A ... mm hypoechoic solid nodule at the appendiceal tip is noted; neuroendocrine tumor should be considered.
On Ga-68 DOTATATE PET-CT, the carcinoid tumor at the appendiceal tip shows marked somatostatin receptor uptake. This imaging modality is used particularly for metastasis screening and staging in tumors >1 cm. The primary tumor and potential regional/distant metastases are detected with high SUV values.
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Marked Ga-68 DOTATATE uptake in the lesion at the appendiceal tip is noted, consistent with somatostatin receptor-positive neuroendocrine tumor.
Criteria
Ki-67 index <3%, mitotic rate <2/10 HPF; usually <1 cm, well-defined
Distinct Features
Excellent prognosis (98-99% five-year survival). Appendectomy is sufficient treatment. CT shows homogeneous enhancement, no necrosis.
Criteria
Ki-67 index >3%, mitotic rate >2/10 HPF; usually >2 cm, invasive margins
Distinct Features
More aggressive biological behavior. Right hemicolectomy may be required. CT may show heterogeneous enhancement, necrosis areas, regional LAP.
Distinguishing Feature
Goblet cell carcinoid behaves more aggressively with diffuse wall thickening and infiltrative growth; classic carcinoid forms focal, well-defined nodule
Distinguishing Feature
Adenocarcinoma shows irregular-margined, heterogeneously enhancing mass usually at the appendiceal base; carcinoid is well-defined, homogeneous, and tip-located
Distinguishing Feature
Acute appendicitis lacks focal mass; diffuse wall thickening and prominent periappendiceal stranding predominate
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
12-monthAppendiceal carcinoid tumor treatment is determined by tumor size: simple appendectomy is sufficient for tumors <1 cm (>98% cure rate); mesoappendix invasion, lymphovascular invasion, and high grade should be evaluated for 1-2 cm tumors; right hemicolectomy is recommended for tumors >2 cm or high-risk features. Carcinoid syndrome is very rare in appendiceal NETs (<5%). Somatostatin receptor scintigraphy (Ga-68 DOTATATE PET-CT) is used for metastasis screening. Serum chromogranin A is used as a follow-up marker.
95% of appendiceal carcinoid tumors are <2 cm with excellent prognosis (5-year survival >95%). Treatment is size-based: <1 cm simple appendectomy is sufficient, 1-2 cm right hemicolectomy considered based on mesoappendix invasion and high Ki-67 index, >2 cm requires right hemicolectomy. Carcinoid syndrome is rare in appendiceal NETs (<1%). Somatostatin analogs (octreotide) are used in the presence of liver metastases.