An unusual case of latero-cervical swelling

Clinical History

A 33-year old male presented with a painless right latero-cervical swelling, which grew slowly over the previous three months. Physical examination revealed a mobile, non-tender mass lesion. The patient’s history was unremarkable and no systemic symptoms or signs were noted. No family history of tumors was reported.

Imaging Findings

High-resolution ultrasound showed, on longitudinal scans, a well-defined, ovoid, homogeneous hypoechoic mass with no posterior acoustic enhancement; its direct connection to the right vagus nerve was hypothesised - see discussion (Fig.1). Color-Doppler examination revealed mild internal vascularity (Fig.2).
MRI demonstrated the presence of an encapsulated mass (23x16x16 mm) within the right carotid space lying between the common carotid artery and the jugular vein, which was displaced postero-laterally. This lesion was homogeneous and isointense to skeletal muscle on T1-weighted sequences and hyperintense on T2-weighted sequences (Figs.3-4). Intravenous administration of gadolinium-based contrast agent demonstrated heterogeneous enhancement (Figs.5-6). Reactive level II and III-level lymph nodes were evident bilaterally, being most prominent on the right side. The contralateral neurovascular bundle appeared morphologically normal.
Ultrasound-guided core-needle biopsy was performed under local anaesthetic and showed a mesenchymal proliferation of neuronal type, with low mitotic activity and no cellular atypia. The immunohistochemical panel was S100-positive, pancytokeratin-negative, smooth muscle actin-negative. These findings were confirmed at histology performed after surgery.

Discussion

Clinical, radiological and biopsy findings correlated with the diagnosis of a neurogenic tumor, in particular a schwannoma arising from the right vagus nerve. Schwannomas are uncommon, benign nerve sheath tumors that occur most frequently between the second and fifth decade [1]. They arise from Schwann cells and are usually solitary and sporadic; multiple schwannomas have been described in association with neurofibromatosis type 2 [2]. 25-45% of schwannomas has been reported to lie in the head and neck, most commonly originating from the vagus nerve [1].

The diagnosis of schwannoma was suspected first for a number of reasons, such as the anatomical location (in the carotid sheath), the apparent connection with the vagus nerve (as seen in Figure 1), the solid iso/hyperechoic echotexture and the lack of intense internal vascularization that are not typical of pathologic lymphnodes.

The lack of specific clinical features gives imaging a key role in the diagnosis and management of schwannomas [3]. Ultrasound typically shows a well-defined, ovoid or round, hypoechoic mass eccentrically arising from the nerve trunk [4]. Ultrasound may also guide minimally-invasive diagnostic procedures, such as core-needle biopsy [5]. MRI provides useful morphologic and topographic information about the schwannoma and adjacent structures. Schwannomas typically appear hypointense to isointense on T1-weighted images and hyperintense on T2-weighted images [1, 4]. Increased distance between the jugular vein and carotid artery, observed in our case, is typical of vagal schwannomas [6].

The differential diagnosis of the lesion was a pathological lymph node or a schwannoma of the vagus nerve. Lymph node biopsy is a routine procedure and presents limited risk. On the other hand, as the schwannoma is a benign tumor of the nerve sheath, it displaces the nerve to one side. Using ultrasound guidance, it is easy to guide a needle into the lesion, thus avoiding adjacent structures, such as vessels within the neurovascular bundle [7].

Tumor surgical excision with preservation of the parent nerve is the treatment of choice, since schwannomas develop eccentrically and may be separated from residual intact nerve fascicles [8, 9].

In our case, tumor excision was successfully performed (Figs.7-8), without any post-surgical complication, and allowed microscopic confirmation of the pre-operative diagnosis.

Although rare, vagal schwannoma should be considered in the differential diagnosis of neck swellings. Ultrasound is valuable for early diagnosis; MRI is essential in pre-operative assessment.

Differential Diagnosis List

Final Diagnosis

Cervical vagal schwannoma

URL:	https://www.eurorad.org/case/13218
DOI:	10.1594/EURORAD/CASE.13218
ISSN:	1563-4086