This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thyroid Tumor, Subject name: Pathology
All of the following are histological features of follicular carcinoma, except: 
Select and explain. 
A. Capsular and vascular invasion, B. Uniform cells forming repetitive follicular pattern, C. Intranuclear grooves and nuclear pseudo-inclusions, D. Huhle cell variant present
C: Intranuclear grooves and nuclear pseudo-inclusions
Answer: C: Intranuclear grooves and nuclear pseudo-inclusions 
Explanation: Intranuclear grooves & nuclear pseudo-inclusions are seen in papillary carcinoma of thyroid, not in follicular carcinoma. Histological features of follicular thyroid carcinoma: Microscopically, most follicular carcinomas are composed of fairly uniform cells forming small follicles containing colloid, quite reminiscent of normal thyroid. Occasional tumors are dominated by cells with abundant granular, eosinophilic cytoplasm - Huhle cells/ oncocytic variant of follicular carcinoma. Nuclei lack features of typical papillary carcinoma & psammoma bodies are not present. There is no reliable cytologic difference b/w follicular adenomas & minimally invasive follicular carcinomas. Making this distinction requires extensive histologic sampling of tumor-capsule-thyroid interface to exclude capsular and/or vascular invasion.