A 38-year-old woman undergoes ultrasound for a left submandibular gland mass. The ultrasound shows a hypoechoic lesion with indistinct margins and heterogeneous echotexture. FNAC is performed and shows malignant cells. Which investigation is most appropriate next to assess for perineural spread and determine surgical margins?

## Staging Investigation After Cytological Diagnosis of Malignant Salivary Gland Tumor **Key Point:** MRI with contrast and DWI is the investigation of choice for staging malignant salivary gland tumors because it best demonstrates perineural spread, soft tissue extension, and bone involvement—critical for surgical planning. ### Why MRI is Superior for Malignant Salivary Gland Tumors 1. **Perineural spread detection**: MRI with contrast shows enhancement along nerve sheaths; DWI detects restricted diffusion in tumor and along nerves—highly sensitive for perineural invasion. 2. **Soft tissue characterization**: Superior contrast resolution compared to CT; clearly delineates tumor from surrounding structures. 3. **Bone marrow involvement**: T1 and T2 sequences detect marrow infiltration better than CT. 4. **No radiation**: Important in younger patients. 5. **Surgical planning**: Defines resection margins and predicts facial nerve involvement. ### Comparison of Staging Modalities | Modality | Perineural Spread | Soft Tissue | Bone Cortex | Bone Marrow | Radiation | |---|---|---|---|---|---| | **MRI + DWI** | ★★★★★ | ★★★★★ | ★★★ | ★★★★★ | None | | **CT** | ★★ | ★★★ | ★★★★★ | ★★ | Yes | | **PET-CT** | ★ | ★★ | ★ | ★ | Yes | | **Frozen section** | ✗ | ✗ | ✗ | ✗ | N/A | **High-Yield:** Perineural spread (PNS) is a hallmark of malignant salivary gland tumors (especially adenoid cystic carcinoma) and is the strongest predictor of local recurrence and poor prognosis. MRI is the imaging modality of choice to detect it. **Clinical Pearl:** If MRI shows perineural spread along the facial nerve, the surgical plan shifts from superficial parotidectomy to total parotidectomy with facial nerve sacrifice if necessary. ### Mnemonic: MRI for Malignant Salivary Gland Tumors **SPREAD** — Superior for Perineural, Soft tissue, Resection planning, Extension assessment, Anatomic detail.