Can retroperitoneal fibrosis present as circumferential wall thickening in the rectum?

Can Retroperitoneal Fibrosis Present as Circumferential Wall Thickening in the Rectum?

Yes, retroperitoneal fibrosis can extend into the pelvis and cause circumferential rectal wall thickening, though this is an atypical and uncommon presentation that may mimic a rectal tumor. 1

Understanding the Typical vs. Atypical Presentations

Classic Retroperitoneal Fibrosis Distribution

• Retroperitoneal fibrosis (RPF) characteristically presents as a fibrotic plaque in the lower lumbar region, typically involving periaortic tissues and causing ureteral obstruction with hydronephrosis 2, 3
• The disease is characterized by replacement of normal retroperitoneal tissue with fibrosis and chronic inflammation, most commonly affecting structures around the abdominal aorta 4, 2
• Approximately 30% of patients present with imaging features suggestive of retroperitoneal fibrosis in the typical retroperitoneal distribution 5

Atypical Pelvic Extension

• Extension of RPF below the pelvic rim to involve the rectum is very unusual but well-documented 1
• In a retrospective review of 30 patients with biopsy-proven RPF, 40% presented with atypical locations, including 7 patients with pelvic involvement 2
• When RPF extends into the pelvis, it can cause compression of the rectum, presenting with constipation as the chief complaint and mimicking a rectal tumor both symptomatically and radiologically 1

Clinical Presentation When Rectum is Involved

Key Distinguishing Features

• Patients may present with constipation as the primary complaint when the fibrotic mass compresses the rectum 1
• Concurrent ureteral involvement is common, with compression causing hydronephrosis (the right ureter was involved in the documented case) 1
• The presentation differs from typical rectal pathology because pain is usually absent unless there is significant obstruction 1

Important Diagnostic Pitfall

• The circumferential rectal wall thickening from RPF can be indistinguishable from a rectal malignancy on imaging studies 1
• Even with CT findings and needle biopsies supporting RPF, exploratory laparotomy may be necessary to definitively rule out malignancy 1
• This is critical because the prognosis for malignant RPF is dismal, while the prognosis for idiopathic or other benign forms is very good 3

Differential Diagnosis Considerations

Distinguishing RPF from Other Conditions

• The differential diagnosis for pelvic fibrotic masses includes malignant RPF (secondary to lymphoma, sarcoma, or metastatic disease), IgG4-related disease, and primary rectal tumors 4, 3
• RPF may be part of a systemic fibrosing disease, with up to 15% of patients having additional fibrotic processes outside the retroperitoneum 2
• In the context of Erdheim-Chester disease (a histiocytic neoplasm), periarterial fibrosis of visceral arteries including the superior mesenteric artery can lead to bowel ischemia, though this represents a different pathophysiologic mechanism 5

Diagnostic Approach

Imaging Strategy

• MRI is the preferred imaging modality to stage and monitor RPF, though CT and PET/CT may also provide value 4
• Contrast-enhanced CT can demonstrate the characteristic findings of RPF, but may not definitively distinguish benign from malignant disease 4, 1
• Advanced imaging techniques such as diffusion-weighted imaging and 18F-FDG PET/MRI can help evaluate disease activity 4

Tissue Diagnosis

• Surgical biopsy remains the only way to definitively establish the diagnosis and distinguish benign from malignant RPF 3, 1
• Needle biopsies may support the diagnosis but are often insufficient to rule out malignancy when rectal involvement is present 1
• Exploratory laparotomy serves both diagnostic and therapeutic purposes, allowing for tissue diagnosis and release of compressed structures like the ureter 1

Clinical Management Implications

When to Suspect Pelvic RPF

• Consider atypical pelvic RPF when a patient presents with constipation, hydronephrosis, and a pelvic mass that appears to involve the retrorectal space 1
• Look for signs of systemic fibrosis or associated conditions (IgG4-related disease, autoimmune disorders, medication history including ergot derivatives) 4, 3
• The combination of rectal compression and ureteral obstruction should raise suspicion for this diagnosis 1

Treatment Considerations

• Treatment may be surgical or medical, with the best outcomes observed in patients receiving both modalities 3
• Surgical intervention may be necessary to release compressed structures and obtain definitive tissue diagnosis 1
• The prognosis is very good for idiopathic and other benign forms of RPF once appropriately diagnosed and treated 3