Abstract
BACKGROUND: Adenoid cystic carcinoma (ACC) of the parotid gland is a rare malignant salivary tumor with aggressive biological behavior, including perineural invasion and delayed metastasis. Despite an 85% 5-year survival rate, long-term prognosis declines to approximately 30%. Preoperative imaging diagnosis remains challenging due to ACC's heterogeneous features on ultrasound, often mimicking benign tumors like pleomorphic adenoma, leading to misdiagnosis. The clinical value of multimodal imaging integration for ACC is underexplored. CASE DESCRIPTION: A 46-year-old female presented with a painless left parotid mass persisting for >1 year. Initial ultrasound revealed a well-defined, hypoechoic solid nodule (measuring 2.5 cm × 2.0 cm × 2.0 cm on sonography) with homogeneous echogenicity, posterior acoustic enhancement, and sparse punctate/linear vascular signals, suggestive of pleomorphic adenoma. Enhanced computed tomography (CT) showed a heterogeneously enhancing mass (+45 HU arterial phase) without invasion. Postoperative pathology confirmed ACC (cribriform/trabecular patterns; SOX10/p63-positive; Ki-67 3%; MYB::NFIB fusion-negative). The patient underwent parotidectomy with facial nerve preservation and adjuvant radiotherapy, with no recurrence at 6-month magnetic resonance imaging (MRI) follow-up. CONCLUSIONS: This case highlights ACC's propensity for "benign-mimicking" sonographic features (well-defined margins, posterior enhancement, hypovascularity), contributing to misdiagnosis. It underscores that integrating elastography (for assessing stiffness), contrast-enhanced ultrasound (for evaluating washout patterns), CT/MRI (for detecting suspicious perineural spread), and molecular biomarkers (e.g., low Ki-67) is crucial to improving diagnostic accuracy and optimizing follow-up management for ACC.