Peripheral pulmonary carcinoid tumor

Peripheral pulmonary carcinoid tumour refer to a subtype of pulmonary carcinoid tumours that arise within the periphery of the lung. They are considered less common than the more centrally-located bronchial carcinoid tumours. 

Clinical presentation

Many patients tend to be asymptomatic  ². Presentation with carcinoid syndrome is extremely rare ⁶. 

Pathology

Peripheral pulmonary carcinoid tumours are considered a neuroendocrine tumour of the lung. They can be typical

• typical pulmonary carcinoid tumours (well-differentiated - common) or atypical
• atypical pulmonary carcinoid tumours (more aggressive - uncommon). 

Risk factors

• smoking: the rate of carcinoid tumours is similar between smokers and non-smokers, although there is an increased incidence of atypical subtype amongst smokers ^5,6

Radiographic features

CT

Most are discovered as an incidental rounded solitary pulmonary nodule. The size at diagnosis can vary but is usually reported to be in the range of 10-30 mm ². Many have a lobulated margin with an average Hounsfield value on postcontrast imaging of ~50 ². Imaging features are often non-specific and tissue diagnosis is essential in determining diagnosis.

Most peripheral carcinoid tumours tend to involve a subsegmental bronchus ². 

Nuclear medicine

FDG-PET

May have a sensitivity of around 75% ⁷. Although most cases will show uptake on an 18-FDG PET, up to a quarter of false negative has been described ². 

Galliun68-Octreotide-PET / ⁶⁸Ga-DOTATATE 

Usually avid and useful for diagnosis ⁸.

Treatment and prognosis

Some authors consider there as complex tumours as a whole which require a multidisciplinary approach and long-term follow-up ¹⁰.

Differential diagnosis

See differentials for a solitary pulmonary nodule.