Multiple sclerosing pneumocytomas: a review

Sclerosing pneumocytoma (SP) is a rare benign low-grade tumour of the lung, and typically presents as single discrete coin lesions on imaging. Multiple SP is an exceedingly rare entity and thus reported sparingly. We review the literature on multiple SP, their clinical presentations, histopathology, relevant differential diagnoses and molecular histogenesis of this entity. SP has a predilection for East Asian origin females who have never smoked. Patients are either asymptomatic or have symptoms such as cough, haemoptysis that may be persistent, chest pain if involving the pleura and presents as discrete coin lesion on chest X-ray. Histologically, they are papillary, solid, angiomatoid or sclerotic, or combinations of these four basic patterns. Multiple lesions have the same or slightly different histological patterns. They can be distributed in either lung, in any lobe and can even be bilateral. AKT-1 molecular pathways are pivotal in their molecular pathogenesis. In this review, we further propose a classification based on five types of distribution of multiple SP.