Lobe-Specific Risk of Malignancy in Parotid Gland Lesions: A Milan System-Based Analysis

Area of Science:

• Head and Neck Pathology
• Cytopathology
• Oncology

Background:

• Parotid gland lesions require accurate diagnosis for appropriate management.
• Fine-needle aspiration cytology (FNAC) is a key diagnostic tool.
• The Milan System for Salivary Gland Cytopathology standardizes reporting.

Purpose of the Study:

• To assess the diagnostic accuracy of FNAC for parotid lesions using the Milan System.
• To eliminate verification bias in diagnostic accuracy assessment.
• To compare the risk of malignancy (ROM) between superficial and deep lobe parotid lesions across Milan categories.

Main Methods:

• Retrospective review of 332 patients with ultrasound-guided FNAC and subsequent surgical excision (2019-2025).
• Classification of FNAC results according to the Milan System.
• Calculation of ROM and diagnostic performance metrics, with subgroup analysis by lobe location. Complete histopathological verification was ensured.

Main Results:

• Malignancy confirmed in 11.1% of cases, with significantly higher frequency in deep lobe (24.6%) vs. superficial lobe (7.9%) lesions (p<0.001), a 3.1-fold increased risk.
• Deep lobe lesions showed higher ROM across most Milan categories, including a 7.3-fold increased risk within the 'benign neoplasm' category (7.3% vs. 1.0%, p=0.009).
• High-risk categories (suspicious/malignant) had similar ROM regardless of anatomical location.

Conclusions:

• FNAC, when classified using the Milan System, offers reliable diagnostic performance for parotid lesions.
• Anatomical location is a critical factor influencing malignancy risk.
• Deep lobe parotid lesions present a substantially higher risk of malignancy across various diagnostic categories.