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Perineural invasion (PNI) refers to the spread of tumor cells along and around nerve sheaths. In the abdomen, this phenomenon is particularly important in pancreatic, biliary, gastric, rectal, and prostate cancers. It is associated with aggressive tumor biology, higher recurrence, and poorer prognosis.

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Pathophysiology

• Tumor cells exploit perineural spaces as “low-resistance pathways” to extend beyond the primary site.
• Mechanisms include:
  • Neurotrophic factors (NGF, GDNF) attracting tumor cells.
  • Tumor-induced nerve remodeling and angiogenesis.
• Spread can occur in a proximal–distal fashion along autonomic plexuses (e.g., celiac plexus, mesenteric plexus).

Common Abdominal Tumors with PNI

• Pancreatic adenocarcinoma (up to 90% show PNI).
• Cholangiocarcinoma and gallbladder carcinoma.
• Gastric carcinoma.
• Rectal carcinoma (especially low rectal tumors).
• Prostate carcinoma (pelvic/abdominal extension).

Radiological Features

CT / MRI (often indirect signs)

• Nerve thickening or asymmetric enlargement.
• Soft tissue stranding or mass along neural pathways (e.g., celiac axis, SMA plexus, mesorectal fascia).
• Obliteration of fat planes around expected nerve locations.
• For pancreatic cancer: encasement of celiac axis/SMA with extension along perivascular neural plexus.