Pulmonary tumourlet

Last revised by David Luong on 9 Jul 2021

Pulmonary tumourlets refer to a type of neuroendocrine cell proliferation in the lung. They are at the benign end of the spectrum of neuroendocrine cell proliferation when diffuse idiopathic pulmonary neuroendocrine cell hyperplasia DIPNECH breach basement membrane but remain less than 5 mm in diameter. 

There is a recognized female predilection. Tumourlets are generally encountered in patients around 60 to 70 years of age 2.

Most patients tend to be asymptomatic at diagnosis.

They are thought to represent tiny peripheral pulmonary carcinoids that differ mainly in size from the larger lesions identified as carcinoid tumors with which they share histological, ultrastructural, and immunohistochemical features. Due to this, they are also called pulmonary carcinoid tumourlets by some authors 4. Tumourlets are usually defined as lesions <5 mm in diameter. They are often multiple.

Tumourlets also lack mitotic activity and do not show necrosis 5.

They often occur in association with airway damage, emphysema and fibrosis.

Pulmonary tumourlets may be seen as small pulmonary nodules and mosaic attenuation secondary to air trapping on CT. 

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