口外型舌下囊肿发病较少,其主要表现为无口内表征的颌下或颏下区囊性肿物,临床上易造成误诊误治。本文报道1例以耳后区巨大肿物为主要临床表现的口外型舌下腺囊肿。患者无明显诱因出现左耳后区反复肿胀半年,皮肤表面破溃后有黄色黏稠液体溢出。首次于北京大学口腔医院就诊时以左侧鳃裂囊肿继发感染为临床诊断,并于2018年11月在全身麻醉下行“左颈部肿物、瘘管切除术”,术中向颈部解剖追踪瘘道至口底舌下腺附近。术后1个月,患者左侧外耳道有可拉丝的“蛋清样”透明黏性液体流出,考虑为舌下腺囊肿口外型,遂于2019年1月在全身麻醉下于口腔内完整摘除同侧舌下腺。经9个月随访,肿物未见复发,外耳道未见溢液。因此,本病例最后诊断为口外型舌下腺囊肿。本病例提示:口外型舌下腺囊肿也可位于耳后区,其最主要的特征是含有“蛋清样”可拉丝的黏性液体,其治疗方法是口内摘除患侧舌下腺。

Plunging ranula is rare and manifests as the submandibular or submental cystic mass, without intra-oral abnormality. It usually causes misdiagnosis and malpractice. This article reported a case of plunging ranula that appeared as a massive mass located behind the left ear. A 6-year-old child presented with recurrent left retroauricular swelling over six months without obvious inducement. The mass showed repeatedly swelling and persistent skin ulcers. Physical examinations described a fluctuant, nontender mass behind the left ear whose size was about 5 cm×5 cm×3 cm. The skin upon the surface of the mass was thin and red, and overflowed yellow slime-like contents. Computed tomography (CT) showed an extensive cystic lesion in the left neck. After local incision and drainage the mass was shrink. With the primary clinical diagnosis of branchial cyst, the patient underwent mass resection through postauricular incision. During the operation, the fistula was traced to the area around the sublingual gland, and the postoperative pathology report demonstrated cystic spaces occurring in soft tissue without lymphoid tissue. One month postoperatively, the patient presented the “egg-white”, wire-drawing transparent viscous fluid outflowing from the left external auditory canal, indicating that the fluid in the external auditory canal originated from the sublingual gland and the disease was the plunging ranula presenting as a giant left retroauricular mass. We readmitted the patient to the hospital and the ipsilateral sublingual gland was completely removed in the mouth under general anesthesia. No clinical evidence of recurrence was found at the end of 9 months follow-up. So far, there is no literature reporting plunging ranula behind ear. This case report describes the clinical manifestation, diagnosis, and differential diagnosis and treatment of a case of plunging ranula, and reveals that, other than the submandibular or submental, plunging ranula also could be found in retroauricular region. The plunging ranula is difficult to fully confirm through a clinical character, and usually easy to be misdiagnosed as other tumors, like lymphatic malformation, venous malformations, etc. Radiographic examination and/or puncture fluid observation are required for identification. “Egg-white”, wire-drawing mucous secretion is the most important characteristic in clinical diagnosis of sublingual gland cyst. However, if sublingual gland resection, i.e. removal of the source of cyst fluid is performed, a good prognosis can be achieved.