In a patient who has undergone long‑course chemoradiotherapy and abdominoperineal resection with permanent colostomy, a contrast‑enhanced computed tomography now shows a presacral soft‑tissue mass (described as rectal growth). What further evaluation is indicated?

Evaluation of Presacral Soft-Tissue Mass After Rectal Cancer Treatment

A presacral soft-tissue mass detected on CECT after abdominoperineal resection with prior chemoradiotherapy requires tissue biopsy for definitive diagnosis, preceded by pelvic MRI with contrast and PET/CT to characterize the lesion and assess for distant metastases.

Immediate Diagnostic Workup

Essential Imaging Studies

• Pelvic MRI with IV contrast is the primary imaging modality for characterizing presacral masses after rectal cancer surgery, as it provides superior soft-tissue contrast to distinguish recurrent tumor from post-treatment fibrosis 1, 2
• PET/CT should be performed to differentiate benign from malignant presacral abnormalities with 100% sensitivity and 96% specificity, and to detect distant metastases that would alter management 1, 3
• MRI demonstrates recurrent tumor as high signal intensity on T2-weighted images, while fibrosis appears as low signal intensity, achieving greater accuracy than CT alone 2

Clinical Assessment Requirements

• Measure serum CEA and CA19-9 levels, as elevated tumor markers support the diagnosis of recurrence 1
• Document specific symptoms including pelvic/perineal pain, altered sensation, or discomfort, which are common manifestations of local recurrence 1
• Perform digital rectal examination if anterior resection was performed (not applicable after abdominoperineal resection) 1

Tissue Diagnosis

Biopsy Indications

• Pathological confirmation is mandatory before proceeding with organ-destructive salvage surgery such as pelvic exenteration 1
• Biopsy should be performed after imaging characterization to guide sampling of viable tumor areas and avoid sampling error 1
• Treatment decisions can proceed based on clinical and imaging findings alone only if less aggressive interventions are planned 1

Imaging Features Requiring Biopsy

• Eccentric, round, or irregular presacral soft-tissue mass measuring 2-20 cm 4
• Marked enhancement after IV contrast administration 4
• New areas of enhancement or lack of spontaneous involution over time 1
• Invasion of surrounding muscle and/or bone 4

Multidisciplinary Team Evaluation

• Comprehensive MDT discussion must include colorectal surgery, medical oncology, radiation oncology, radiology, and potentially urology, gynecology, or plastic surgery depending on the extent of disease 1
• Apply the Leeds classification system to categorize recurrence as central type (confined to pelvic organs), lateral wall type (involving pelvic sidewall structures), sacral side type (presacral with sacral involvement), or mixed type 1
• Assess surgical resectability based on anatomical involvement, with central type having the highest resection rate and lateral type the lowest 1

Treatment Algorithm Based on Findings

If Biopsy Confirms Recurrence Without Distant Metastases

• Resectable disease with prior chemoradiotherapy: Proceed directly to surgery with possible postoperative chemotherapy 1
• Unresectable disease with prior chemoradiotherapy: Offer palliative treatment and reassess for potential resection after response 1
• Patients intolerant to surgery should receive chemotherapy alone 1

If Distant Metastases Are Detected

• Manage according to synchronous metastatic rectal cancer treatment principles 1
• Systemic therapy becomes the primary treatment modality 1

Common Pitfalls to Avoid

• Do not rely on CT alone to distinguish recurrent tumor from post-surgical fibrosis, as CT cannot determine with certainty whether presacral soft-tissue density represents recurrence 5
• Avoid PET/CT as the sole imaging modality for local assessment, as physiologic FDG uptake in displaced pelvic organs causes false-positive interpretations in 35% of cases when PET is used without CT correlation 3
• Do not delay biopsy if imaging demonstrates concerning features and curative-intent surgery is being considered, as pathological confirmation prevents unnecessary morbidity from surgery for benign conditions 1
• Recognize that enhancement patterns may be misleading in the immediate post-treatment period, as completely treated lesions can show persistent enhancement for weeks to months 1

Surveillance Considerations

• The majority of recurrences occur within 2-3 years after initial treatment, with recurrence rates of 10-30% after chemoradiotherapy 1
• Presacral masses detected more than 6 months post-treatment are more likely to represent true recurrence rather than treatment-related changes 1