Pulmonary carcinoid tumor is a neoplasm originating from bronchial neuroendocrine cells with low to intermediate malignant potential. It constitutes 1-2% of all lung tumors. Typical carcinoid (90%) is low-grade with excellent prognosis, while atypical carcinoid (10%) has a more aggressive course. Mean age at diagnosis is 45-55 years with minimal gender predilection. 75-80% of cases are centrally located endobronchially and may present with obstructive pneumonia or hemoptysis. Carcinoid syndrome (5%) — flushing, diarrhea, wheezing — is rarer in peripheral tumors.
Age Range
20-60
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Pulmonary carcinoid originates from Kulchitsky cells (neuroendocrine cells) in the bronchial mucosa. Typical carcinoid is well-differentiated and slow-growing — characterized by low mitotic index (<2/10 HPF) and absence of necrosis. Slow growth produces a well-defined, smooth-contoured mass. The tumor's intense vascularity (rich capillary network) explains the prominent homogeneous enhancement on contrast-enhanced CT — this feature is critical in differentiating from other lung nodules. Endobronchial growth causes luminal obstruction, distal atelectasis, and obstructive pneumonia. Calcification occurs in approximately 30% of cases through dystrophic mechanism. Atypical carcinoid shows higher mitotic activity (2-10/10 HPF) and focal necrosis — reflected as heterogeneous enhancement and irregular margins. Neuroendocrine granules express somatostatin receptors — forming the basis for octreotide scintigraphy (OctreoScan) positivity and therapeutic somatostatin analog response.
Intense, homogeneous enhancement with >40 HU increase in a lung nodule — hypervascular neuroendocrine tumor signature. Distinctly different from the heterogeneous and less intense enhancement of adenocarcinoma and squamous cell carcinoma.
Centrally located (75-80%), well-defined, round/oval, homogeneous soft-tissue density mass in the bronchial lumen or peribronchial region. Size usually 2-5 cm. Peripheral carcinoids (20-25%) are more common in lower lobes and tend to be smaller.
Report Sentence
A well-defined, homogeneous-density endobronchial mass measuring approximately ___ cm in the main/lobar bronchial lumen is identified, and central carcinoid tumor should be the primary consideration.
Marked homogeneous enhancement — typically >40 HU increase (60-80 HU in some series). Enhancement intensity reflects the hypervascular nature of the tumor and is the most important CT criterion in differentiation from other lung nodules (adenocarcinoma, metastasis).
Report Sentence
The lesion demonstrates marked homogeneous enhancement (___ HU increase), consistent with a hypervascular tumor; carcinoid tumor should be considered in clinical context.
Calcification is observed in approximately 30% of cases. Pattern may be central, eccentric, or diffuse. Punctate calcifications are most common. Ossification can rarely be seen. The presence of calcification does not definitively exclude malignancy but supports the diagnosis.
Report Sentence
Calcification focus/foci within the lesion are identified, consistent with a slow-growing neoplasm (carcinoid tumor).
Distal atelectasis (40-60%) or obstructive pneumonia may be observed in central endobronchial carcinoids. Bronchial obstruction causes lobar or segmental collapse, mucus plugging, and post-obstructive infection. The tumor itself is visualized proximal to the obstruction site.
Report Sentence
Endobronchial mass in the ___ bronchus with distal atelectasis/obstructive pneumonia findings is observed; central carcinoid tumor causing bronchial obstruction should be considered in the differential diagnosis.
Intermediate to high signal intensity on T2-weighted sequences. Homogeneous signal pattern is characteristic of typical carcinoid. Necrotic areas in atypical carcinoid may show focal high T2 signal. Moderate diffusion restriction is observed on DWI.
Report Sentence
The lesion demonstrates homogeneous intermediate-high signal intensity on T2-weighted images with moderate diffusion restriction on DWI; findings are consistent with carcinoid tumor.
FDG uptake is variable: low to moderate in typical carcinoid (SUVmax 1.5-4), moderate to high in atypical carcinoid (SUVmax 4-10). Low FDG uptake is characteristic of typical carcinoid and important in differentiating from high-grade malignancies. Octreotide scintigraphy (OctreoScan) or 68Ga-DOTATATE PET/CT has >90% sensitivity for somatostatin receptor-positive carcinoids.
Report Sentence
Low/moderate FDG uptake (SUVmax ___) is observed in the lesion, consistent with a low-grade neuroendocrine tumor (typical carcinoid); confirmation with somatostatin receptor imaging (68Ga-DOTATATE PET/CT) is recommended.
Iceberg phenomenon — the endobronchial component appears small while the peribronchial/extrabronchial component is much larger. Observed in 40-50% of central carcinoids. The tumor may extend through the bronchial wall to show mediastinal or hilar spread.
Report Sentence
Peribronchial extension of the endobronchial mass is observed ('iceberg phenomenon'), with total mass size much larger than suggested by the intraluminal component.
Criteria
Mitosis <2/10 HPF, no necrosis. WHO Grade 1 neuroendocrine tumor. 10-year survival >90%.
Distinct Features
Well-defined margins, homogeneous enhancement, low FDG uptake (SUVmax <4). Usually central endobronchial. Calcification more common (30%). Metastasis rare (5-15% lymph node metastasis).
Criteria
Mitosis 2-10/10 HPF and/or focal necrosis. WHO Grade 2 neuroendocrine tumor. 10-year survival 50-70%.
Distinct Features
Larger size, heterogeneous enhancement (necrotic areas), irregular margins may be present. Peripheral location more common. Moderate-high FDG uptake (SUVmax 4-10). Lymph node metastasis 30-50%, distant metastasis 20-25%.
Criteria
Located in lung periphery (parenchymal). 20-25% of cases. Usually asymptomatic, incidental finding.
Distinct Features
Well-defined round/oval nodule (1-3 cm), no obstructive findings (not endobronchial). Intense homogeneous enhancement is preserved. More common in lower lobes. Carcinoid syndrome is rare.
Criteria
Size <5 mm. Originates from neuroendocrine cell hyperplasia. Usually incidental histological finding.
Distinct Features
Usually not visible on CT (<5 mm). May be multiple, especially in the setting of bronchiolitis obliterans and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH). Malignant transformation extremely rare.
Distinguishing Feature
Adenocarcinoma shows heterogeneous enhancement (<40 HU increase), spiculated margins, and ground-glass component; carcinoid enhances homogeneously and intensely (>40 HU increase) with smooth margins.
Distinguishing Feature
Squamous cell carcinoma, although central, shows cavitation, necrosis, and irregular margins; carcinoid is solid, homogeneous, and rarely cavitary. Squamous is strongly associated with smoking, carcinoid weakly. FDG uptake is very high in squamous (SUVmax >10).
Distinguishing Feature
Hamartoma shows fat content (<-40 HU) and popcorn calcification — carcinoid does not contain fat. Hamartoma is peripherally located with minimal enhancement, while carcinoid enhances intensely.
Distinguishing Feature
Metastases are usually multiple and bilateral; solitary carcinoid is a single lesion. Enhancement in metastases is variable and usually not as intense as carcinoid. Known primary malignancy history supports metastasis.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
6-monthTypical carcinoid has excellent prognosis — surgical resection (lobectomy or sleeve resection) is curative with >90% 10-year survival. Bronchoscopic biopsy is diagnostic for endobronchial tumors, but bleeding risk exists due to hypervascularity. Atypical carcinoid is more aggressive requiring mediastinal lymph node dissection. Octreotide scintigraphy or 68Ga-DOTATATE PET/CT should be standard for staging. Somatostatin analogs (octreotide LAR) provide symptom control in carcinoid syndrome.
Typical carcinoids have excellent prognosis (5-year survival >90%). Surgical resection is curative. Atypical carcinoids have worse prognosis. Somatostatin analogs can be used for functional tumors.