Published online Apr 28, 2019. doi: 10.3748/wjg.v25.i16.1997
Peer-review started: November 12, 2018
First decision: December 28, 2018
Revised: February 12, 2019
Accepted: February 15, 2019
Article in press: February 16, 2019
Published online: April 28, 2019
Chronic radiation proctopathy (CRP) occurs as a result of pelvic radiation therapy and is associated with formation of abnormal vasculature that may lead to persistent rectal bleeding. While incidence is declining due to refinement of radiation delivery techniques, CRP remains one of the major complications of pelvic radiation therapy and significantly affects patient quality of life. Radiofrequency ablation (RFA) is an emerging treatment modality for eradicating abnormal vasculature associated with CRP. However, questions remain regarding CRP pathophysiology and optimal disease management.
This pilot study utilizes ultrahigh-speed optical coherence tomography (OCT) and OCT angiography (OCTA) to investigate microvascular features of normal versus CRP patients and how they respond under endoscopic RFA treatment.
We utilized OCT and OCTA for assessing subsurface depth-resolved microvasculature around the dentate line and rectum of normal patients as well as CRP patients who were RFA-naïve or under treatment. OCTA can image normal and abnormal microvasculature in the mucosal and submucosal layers of the rectum, providing information not available by endoscopy. Blinded reading of vascular features were performed to assess incidence of abnormal features in RFA treatment naïve CRP as well as response under treatment. Association with endoscopic rectal telangiectasia density scoring was also investigated.
Two patients with normal rectum and 8 patients referred for, or undergoing endoscopic treatment with RFA for CRP were imaged with ultrahigh-speed OCTA/OCT over a total of 15 OCT/colonoscopy visits (2 normal patients, 5 RFA-naïve CRP patients, 8 RFA-follow-up visits). Imaging was performed using a prototype ultrahigh-speed OCT instrument at 600 kHz axial scan rate using a small imaging catheter. OCTA enabled depth-resolved microvasculature imaging using motion contrast from flowing blood, without requiring injected dyes.
OCTA visualized normal vasculature with regular honeycomb patterns versus abnormal distorted honeycomb patterns with ectatic and tortuous microvasculature in the rectal mucosa. Normal arterioles and venules < 200 μm in diameter versus abnormal heterogenous enlarged arterioles and venules > 200 μm in diameter were visualized in the submucosa. Abnormal mucosal vasculature occurred in 0 of 2 normal patients and 3 of 5 RFA-naïve patients, while abnormal submucosal vasculature occurred more often, in 1 of 2 normal patients and 5 of 5 RFA-naïve patients. After RFA treatment, vascular abnormalities decreased, with abnormal mucosal vasculature observed in 0 of 8 RFA-follow-up visits and abnormal submucosal vasculature observed in only and 2 of 8 RFA-follow-up visits.
This study demonstrated that OCTA can visualize depth-resolved normal and abnormal microvasculature around the dentate line and rectum associated with CRP and treatment response. Submucosal vascular abnormalities seemed more strongly associated with CRP than mucosal vascular abnormalities. Both mucosal and submucosal abnormal vasculature was observed to normalize after RFA treatment. However, these observations must be viewed with caution since this was a retrospective study with a small patient enrollment. Further larger scale, prospective, longitudinal studies are warranted.
The role of mucosal vs submucosal vascular alterations in CRP remains an open question in pathophysiology. Submucosal vasculature is not visible endoscopically and therefore OCTA/OCT provides a unique modality for assessing CRP. Furthermore, OCTA does not require injected dyes and is well suited for longitudinal studies. It can rapidly imaging large regions of rectum to yield integrated microstructural and microvascular maps. These advantages suggest that OCTA/OCT could be a viable tool for investigation of CRP to elucidate pathophysiology as well as potentially plan treatment and assess response.