Peripheral pulmonary carcinoid tumor

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

Clinical presentation

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

Pathology

Peripheral pulmonary carcinoid tumors are considered a neuroendocrine tumor of the lung. They can be:

• typical pulmonary carcinoid tumors (well-differentiated, common)

• atypical pulmonary carcinoid tumors (more aggressive, uncommon) 

Risk factors

• smoking: the rate of carcinoid tumors 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 post-contrast imaging of ~50 ². Imaging features are often non-specific and tissue diagnosis is essential in determining diagnosis.

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

Calcification may be present in a small percentage (~11% ) of tumors ².

Some authors have suggested a "bronchial triangle sign" which may assist in diagnosis ¹².

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. 

⁶⁸Ga-Octreotide-PET / ⁶⁸Ga-DOTATATE 

Usually avid and useful for diagnosis ⁸.

Treatment and prognosis

Some authors consider these as complex tumors, requiring a multidisciplinary approach and long-term follow-up ¹⁰.

Differential diagnosis

In some situations for CT appearances consider:

• pulmonary hamartoma

• enlarged intrapulmonary / bronchopulmonary node (e.g. station 12,13,14)

For a broader differential see differentials for a solitary pulmonary nodule.