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What caused an otherwise healthy 23-year-old man to suddenly develop a large painless mass on the left side of his neck? That's what Jianyong Zhang, MD, and Xin Zhu, MM, of Guizhou Provincial People's Hospital in Guiyang, China, needed to determine.

When the patient presented at the vascular thyroid surgery clinic for examination, he told clinicians that the mass had developed suddenly 10 days prior. Although it was not painful, he described feeling uncomfortable tightness on the left side of his neck, the authors explained in .

He had not experienced any recent injuries or incidents of neck trauma or impact. Furthermore, his medical history did not reveal any previous hematological disorders. The patient underwent an ultrasound examination, which revealed a solid regularly shaped mass with well-defined boundaries, located in the left lobe of the thyroid gland. In addition to distinct boundaries, the mass was characterized by heterogeneous echogenicity and observable blood flow signals.

They performed a CT scan of the patient's neck, which revealed "heterogeneous density mass shadows within the soft tissue region near the left lobe of the thyroid, exhibiting distinct boundaries measuring 53 × 41 × 88 mm," the authors wrote. On follow-up with enhanced CT, there was no significant enhancement of the cystic components of the mass.

The medical team considered several differential diagnoses, including lymphoma, a venous malformation, vagal schwannoma, or a thyroid cyst. Subsequently, in an effort to address his persistent symptoms, the patient requested that the mass be surgically removed. He underwent open surgical resection of the mass, toward making a definitive diagnosis and determining appropriate treatment.

Surgeons removed a large tumor with morphology they believed to be a schwannoma; it was located adjacent to the vagus nerve, within the cervical sheath. A specimen sent to the lab for histological analysis confirmed the presence of "a distinctly demarcated mass, while intraoperative pathology suggested the presence of a spindle cell tumor, specifically identified as a schwannoma."

Clinicians' diagnosis was supported by immunohistochemical characteristics that confirmed a vagal schwannoma:

• S100 and SOX10 positive
• p53 negative
• Ki-67 proliferation index of 3%

Discussion

"A schwannoma, which is alternatively referred to as neuroschwannoma, neurilemmoma, or neurinoma of Verocay, is a nonmalignant neoplasm that arises from Schwann cells located in the cranial, peripheral, and autonomic perineural regions," the authors wrote.

People can develop these benign neoplasms along any cranial, peripheral, or autonomic nerve in the body, except for the olfactory and optic nerves, which do not contain Schwann cells, the authors noted. Data suggest that 25% to 45% of schwannomas are extracranial, affecting the head and, most often, the side of the neck. As this case reflects, a vagal schwannoma is an indolent benign tumor that develops on the neck, occurs on its own, and is typically asymptomatic.

To date, the epidemiological characteristics of cervical vagal nerve schwannomas have not been defined, Zhang and Zhu said. However, findings of a suggested that both sexes are equally affected. And while vagal nerve schwannomas can affect people of any age, they are somewhat more common in individuals ages 30 to 50.

Benign schwannomas rarely become malignant, although this transformation has been reported. As benign neoplasms, schwannomas typically progress gradually, growing in size by about 3 mm yearly.

The patient reported in this case presented with acute onset of an unusually large tumor, the authors noted, which had previously been overlooked as a schwannoma before surgery. Schwannomas located on the vagal nerve generally require only . This patient has had no recurrences.

have identified use of various , including ultrasound, CT, MRI, and fine-needle aspiration cytology (FNAC), the authors said.

"Nevertheless, it is worth noting that FNAC often poses challenges in accurately characterizing schwannomas, and some authors have found it to be of limited assistance in the diagnostic process," they wrote.

Conversely, MRI represents "the most sensitive and specific preoperative" diagnostic tool, because it allows more precise identification of the originating nerve, they added.

Prior to undergoing surgery, the patient in this case declined both MRI and FNAC. Zhang and Zhu explained that use of FNAC in this patient was associated with a "potential risk of considerable hemorrhaging associated with the mass."

Thus, they noted that "use of surgical resection accompanied by microscopic tissue examination proved indispensable in establishing the diagnosis of schwannoma."

In addition, supported the schwannoma diagnosis, in that test results were positive for S100, SOX10, PGP9.5, and H3K27Me3, and negative for NF, SMA, p53, and CKpan and a Ki-67 proliferation index of 3%. "In this case, the presence of S100 and SOX10 proteins was observed through immunohistochemistry, which serves as a valuable for Schwann cells," the authors wrote.

Most malignant peripheral nerve sheath tumors (MPNSTs) are immunoreactive for Ki-67 in 5% to 65% of tumor cell nuclei, they noted. In contrast, "benign peripheral nerve sheath tumors display nuclear staining not exceeding 5%."

Furthermore, a significant proportion of MPNSTs exhibit "nuclear staining for p53 ranging from 5% to 100%, whereas no benign peripheral nerve sheath tumors exhibit nuclear staining exceeding 1%," they added.

In this case, immunohistochemistry assessments -- conducted to exclude the possibility of an MPNST -- were negative for the p53 antigen, while the Ki-67 proliferation index was 3%, the authors concluded.

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