Postirradiation changes in the pelvic wall. Findings on MR

Area of Science:

• Radiology
• Oncology
• Medical Imaging

Background:

• Radiation therapy is a common treatment for anal and rectal cancers.
• Post-treatment imaging is essential for monitoring disease recurrence and treatment effects.
• Distinguishing radiation-induced changes from tumor progression is a clinical challenge.

Purpose of the Study:

• To characterize the magnetic resonance imaging (MRI) findings of postirradiation changes in the pelvic wall.
• To differentiate normal postradiation changes from tumor infiltration in patients treated for anal or rectal cancer.

Main Methods:

• Retrospective review of MR images from 45 patients treated with radiation therapy for anal or rectal cancer.
• Analysis of T1-weighted and T2-weighted images to identify changes in bone marrow, presacral space, and pelvic wall muscles.
• Correlation of imaging findings with the timing of radiation therapy.

Main Results:

• High signal intensity in bone marrow on T1-weighted images was consistently observed, attributed to fatty replacement.
• Presacral edema was noted in 7 of 36 patients, increasing in frequency at later time points (4-6 weeks post-irradiation).
• Pelvic wall muscles showed high signal intensity on T2-weighted images, indicative of edema, most frequently observed more than 6 weeks after irradiation and subsiding over a year later.

Conclusions:

• Postirradiation MRI demonstrates characteristic changes in the pelvic wall, including bone marrow and muscle edema.
• These findings, particularly presacral edema and muscle signal changes, can mimic tumor infiltration.
• Understanding these normal postradiation changes is vital for accurate interpretation of pelvic MRIs and avoiding misdiagnosis of recurrent cancer.