| Objectives:(1) To describe imaging appearances of pulmonary intersegmental planes (IPs) on thoracic computed tomographic (CT) scans and analyze the reasons leading to the visualization of IPs within normal lungs in terms of aging and anatomy.(2) To evaluate the substance of pulmonary intersegmental plane and uncover the cause accounting for the partial visualization of intetrsegmental plane on thoracic CT.Materials and Methods:(1) A retrospective review was undertaken of104multidetector thoracic CT scans of two groups (older group, over65years; younger group, under55years). The number, location and appearance rate of IPs were assessed. Group comparisons were made, and linear regression analysis was used to assess relationships between age and visualization of IPs.30lung samples (10×10×10mm3) from autopsy were scanned by micro-CT. The thicknesses of IPs were measured. The independent-t test was made to assess the significant difference of the thickness between visible and invisible IPs.5fetal specimens of17-21weeks gestational age (GA) were scanned by7.0T Magnatic Resonance (MR) to determine the congenital difference of thickness of IPs.(2) CT images from a fresh cadaver were reviewed to identify the visible intersegmental planes. Totally,32lung samples were excised on injected lungs.20of them (visible intersegmental plane=4; invisible intersegmental plane=16) were used for micro-CT scanning in order to acquire microanatomy of visible and invisible intersegmental plane. Another6,4and2specimens were for macroscopic observation, histology and electron microscopy individually. Micro-CT images were analyzed and measured by CTAn software. The three-dimensional visualization model was obtained with3Dmed software.Results:(1) Within the right lung, the visible IPs were seen at S1-S3, S4-S5and S7-S10, and their appearance rates were71.2%,54.8%, and70.2%individually. Within the left lung, they were visible at S1+2-S3, S4-S5, S7-S8and S7-S10, their appearance rates were39.4%,64.4%,18.3%and89.4%individually. Appearance rates of visible IPs on thoracic CT were of no significant differences between younger group and older group. The thicknesses of visible and invisible IPs were681.3±75.3μm and221.7±54.1μm individually. The thicknesses of visible IPs were significantly thicker than invisible IPs (P<0.05). Visible IPs were also seen on fetal lung7.0T MRIs.(2) Varied methods show that the intersegmental plane is composed of three layers. Alveolar wall and collagenous fibers serve as the coat layers and medial layer individually. Collagenous fibers constitute the main part of the plane and feature the intersegmental plane as a layer of loosen and low-density septum. The thickness of visible intersegmental plane is significantly larger than that of invisible different (P<0.05). The largest thickness of invisible and visible intersegmental plane is individually233.7±46.2μm and742.4+108.9μm. The smallest thickness of invisible and visible intersegmental plane is individually150.5±37.6μm and464.6±180.0μm.Conclusion:The thickness of IP and variation of intersegmental veins were closely related the visualization of IPs on thoracic CT scans. Aging was excluded as the possible reason. Micro-CT images show the microarchitecture of intersegmental plane clearly. The visible intersegmental plane is featured the thicker and looser medial layer, which contribute to the visualization of intersegmental plane on thoracic CT. |
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