淋巴结（LN）转移引起的颈部肿胀是头颈部肿瘤的一个初期症状，有时原发肿瘤并不明显。对于未知原发部位的LN转移的影像学检查的目的是识别原发肿瘤或发现其缺失，从而达到正确的诊断和最佳治疗效果。本文作者讨论了在未知原发颈部LN转移病例中鉴别原发肿瘤的诊断影像学方法。LN转移的分布和特征可能有助于定位原发部位。未知原发的LN转移通常发生在II和III级淋巴结，而且最近的报道多与口腔咽癌的人乳头瘤病毒（HPV）阳性鳞状细胞癌相关。另一个提示来自HPV相关的口咽癌的LN转移的特征性影像学表现是LN转移的囊性变化。其他表现出特征性影像学表现的病变，如钙化，可能有助于预测组织学类型和定位原发部位。在IV和VB级淋巴结转移的情况下，还必须考虑头颈部区域外的原发病灶。在影像学上发现解剖结构的破坏是发现小黏膜病变或亚黏膜肿瘤的线索，同时荧光素18荧光脱氧葡萄糖PET/CT还有助于鉴定原发肿瘤。这些鉴别原发肿瘤的影像学检查方法能够迅速识别原发病灶，协助临床医生做出正确的诊断。© RSNA，2023本文的测验问题可通过在线学习中心获得。

Neck swelling due to lymph node (LN) metastasis is one of the initial symptoms of head and neck cancer, and in some cases, the primary tumor is not clinically evident. The purpose of imaging for LN metastasis from an unknown primary site is to identify the primary tumor or detect its absence, which leads to the correct diagnosis and optimal treatment. The authors discuss diagnostic imaging approaches for identifying the primary tumor in cases of unknown primary cervical LN metastases. The distribution and characteristics of LN metastases may help locate the primary site. Unknown primary LN metastasis often occurs at nodal levels II and III, and in recent reports, these were mostly related to human papillomavirus (HPV)-positive squamous cell carcinoma of the oropharynx. Another characteristic imaging finding suggestive of metastasis from HPV-associated oropharyngeal cancer is a cystic change in LN metastases. Other characteristic imaging findings such as calcification may help predict the histologic type and locate the primary site. In cases of LN metastases at nodal levels IV and VB, a primary lesion located outside the head and neck region must also be considered. One clue for detecting the primary lesion at imaging is the disruption of anatomic structures, which can help in identifying small mucosal lesions or submucosal tumors at each subsite. Additionally, fluorine 18 fluorodeoxyglucose PET/CT may help identify a primary tumor. These imaging approaches for identifying primary tumors enable prompt identification of the primary site and assist clinicians in making the correct diagnosis. © RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.