A 62-year-old man with a history of laryngeal carcinoma (T3N1M0) has completed radiation therapy 6 months ago. He now presents with persistent hoarseness and dysphagia. Flexible laryngoscopy shows an irregular lesion at the site of the original tumor. What is the most appropriate next investigation to differentiate residual/recurrent disease from radiation-induced changes?

Explanation

## Investigation of Choice for Suspected Recurrent/Residual Laryngeal Carcinoma **Key Point:** PET-CT is the most appropriate investigation to differentiate residual/recurrent laryngeal carcinoma from benign radiation-induced changes. It combines metabolic activity (FDG uptake) with anatomical detail. ### Why PET-CT in Post-Radiation Surveillance? **High-Yield:** In the post-radiation setting (within 6–12 months), distinguishing recurrent tumor from radiation edema, fibrosis, and necrosis is challenging on anatomical imaging alone. 1. **Metabolic imaging advantage** — FDG-PET detects increased glucose metabolism in viable tumor cells, not in scar tissue or radiation-induced inflammation 2. **High sensitivity and specificity** — reported sensitivity 85–95% and specificity 80–90% for detecting recurrent laryngeal carcinoma [cite:Robbins 10e Ch 7] 3. **Whole-body staging** — simultaneously assesses for distant metastases and nodal recurrence 4. **Guides biopsy decision** — if PET-CT is positive, biopsy is indicated; if negative, close follow-up is safer than biopsy ### Diagnostic Approach Algorithm ```mermaid flowchart TD A[Post-radiation hoarseness + lesion on laryngoscopy]:::outcome --> B{Suspicion of recurrence?}:::decision B -->|High| C[PET-CT for metabolic assessment]:::action C --> D{FDG uptake present?}:::decision D -->|Yes| E[Biopsy to confirm recurrence]:::action D -->|No| F[Benign radiation changes; close follow-up]:::outcome B -->|Uncertain| C E --> G[Salvage surgery or chemotherapy]:::action F --> H[Clinical and imaging surveillance q3-6 months]:::action ``` ### Comparison of Investigations in Post-Radiation Setting | Investigation | Advantage | Limitation | |---|---|---| | **PET-CT** | Metabolic imaging; distinguishes viable tumor from scar | Cost; radiation exposure; not available everywhere | | **DW-MRI** | Good soft tissue contrast; restricted diffusion in tumor | Difficult to distinguish early recurrence from edema; longer acquisition time | | **Repeat biopsy** | Definitive histology | Risk of non-healing ulceration; radiation-induced necrosis; may miss small recurrences | | **Ultrasound + FNA** | Accessible; low cost | Poor visualization through scar tissue; limited for laryngeal lesions | **Clinical Pearl:** Biopsy in the immediate post-radiation period (< 3 months) is avoided because: - Radiation-induced ulceration may not heal - Histology may show dysplasia without malignancy - Risk of laryngeal stenosis Wait 6+ months post-radiation, then use PET-CT to guide biopsy decision. **Mnemonic:** **PET-CT for POST-radiation** — Positron Emission Tomography–Computed Tomography is the investigation of choice in the post-radiation setting to differentiate recurrence from benign changes. **Warning:** ~~Biopsy immediately after radiation~~ is not recommended due to risk of non-healing and radiation necrosis. PET-CT should guide the decision to biopsy.