Patient selection: follicular neoplasm
Features of true vascular invasion:
(1) tumor cells present within a blood vessel wall with invasion through the endothelium
(2) thrombus adherent to the intravascular tumor
The number of foci of true vascular invasion is often limited, so the entire lesion should be submitted for histology and the sections carefully examined. Immunostaining with anti-CD34 or other marker can highlight the endothelium.
Examples of pseudo-vascular invasion:
(1) tumor cells bulging into a vascular space under an intact endothelium
(2) displacement of tumor cells into a vascular space
(3) endothelium proliferation and/or fibrosis entrapping adjacent follicular cells following a fine needle aspirate (FNA). Although a thrombus could form after an FNA the time interval between the FNA and surgery is usually long enough for this to be resorbed.
About a third of patients with a well-differentiated follicular carcinoma will develop distant metastases. About half of patients with a poorly differentiated follicular carcinoma will develop distant metastases.
