Materials and methods
This retrospective, observational, descriptive longitudinal study was
approved by our institutional Research Ethics Board. We performed a free
word search of our radiological report database using the terms
”subpleural cysts”, “peripheral cysts” or ”subpleural blebs” over a
21-year period (2001-2022) at a tertiary level pediatric hospital. We
limited the search to children under 3 years of age at their initial
chest CT. Patient demographics, clinical information and laboratory
work-up including genetics and histopathology were extracted from
patients’ charts. Echocardiographic and cardiac catherisation reports
were reviewed for the documentation of underlying congenital heart
disease (CHD) and/or pulmonary artery hypertension (PAH).
All CT scans, including studies acquired at external institutions, were
performed on multi-detector scanners. Scanners differed with upgraded
technology due to a long study duration of over 22 years. All cases were
performed as helical scans, reconstructed to 2.5mm thickness for review
of mediastinal/soft tissue windows using approximate window width 350,
level 40 and reconstructed to 0.625-2.5mm thickness for review on a lung
algorithm (approximate window-width 1500, level -500). Intravenous
contrast was given in most cases, depending on the clinical question.
Our primary endpoint was the presence or absence of multiple 1-4 mm
air-filled subpleural cysts.
All studies performed at our institution utilised a CT dose-adjusted
algorithm according to the body weight of the child. More recent studies
were performed using CT scanners that provided additional automatic
exposure control (AEC) with modulation of the tube-current depending on
the thickness of the body part examined. As a result, mAs varied between
80-150 with a 120 kVp. As all patients were under the age of 4, scans
were performed either using a “feed and sleep” approach, sedation or
under general anaesthesia (GA). Non-GA cases were acquired in quiet
breathing and GA cases were acquired in full inspiration, either via
endotracheal tube or positive pressure mask. Prospective ECG-gated
triggering was done in cases performed with a cardiac CT protocol.
All CT images were qualitatively analysed for the presence and
distribution of subpleural cysts. The size of the largest cyst was
recorded. The heart and mediastinal structures were evaluated for
structural cardiac abnormalities, in correlation with data from
echocardiographic examinations. Ancillary findings of mosaic
attenuation, ground glass opacities and pleural effusion or pneumothorax
were also recorded. Follow-up CT’s in the available cases were compared
for the interval status of cyst size and distribution. All images were
analysed independently by three pediatric radiologists with a specialty
interest in pulmonary imaging (33 years’ experience, 3 years’
experience, and a fellow in pediatric imaging). The radiologists were
blinded to the clinical information and to each other’s interpretations,
with a consensus on final image interpretation.
Subpleural cysts were differentiated from subpleural lines seen in
children with lymphatic distension due to lymphangiectasia by set
criteria consisting of the lack of fissural thickening, lack of pleural
effusions, lack of basal septal thickening creating typical hexagonal
opacities, and lack of ‘Kerley’ lines in our cohort of children with
peripheral cystic disease.
Demographic characteristics were summarized using descriptive
statistics.