Myopericytoma of the neck - a very rare tumour in a deep location

A 41-year-old woman presented with a slowly growing left lateral cervical mass. She had noticed the mass 10 months prior, and it had gradually enlarged since then. On physical examination, a solid and ovoid mass was found in the left carotid triangle, with well-defined margins, and with carotid pulse transmission.

Grayscale ultrasound identified an inhomogeneous, well-defined and markedly hypoechoic mass in the left lower neck, between the common carotid artery and internal jugular vein. The mass showed hypervascularity on power Doppler (PD) US (Fig. 1).
Axial T1-weighted imaging post gadolinium demonstrated avid enhancement of the mass (Figs. 2 and 3). On T2-weighted imaging it is of high signal intensity compared to muscle (Fig. 4). Axial diffusion-weighted imaging did not show restricted diffusion (Fig. 5).
The surgical team decided to perform resection of the mass and submit it for histopathological examination. A definitive diagnosis of myopericytoma was made.

Myopericytoma is a rare mesenchymal neoplasm, which belongs to the subgroup of perivascular tumours in the World Health Organization classification (2002) of soft tissue tumours. It is characterised by perivascular proliferation of pericytic cells of myoid differentiation. In contrast to haemangiopericytoma, myopericytoma is a truly pericytic neoplasm, which represents a continuum on the spectrum between myofibromatosis, glomus tumour and angioleiomyoma [1]. Myopericytomas have a propensity to occur as single or multiple nodules, superficially located in the dermis and subcutaneous layer of the lower extremities, followed in order by upper extremities, head and neck, and trunk, but unusual sites, such as intracranial and intravascular sites, have also been reported [1].
Clinical findings are nonspecific. It has been described that myopericytoma tends to have a female predilection and that it presents as a slow growing asymptomatic cervical mass.
B-mode ultrasound shows a well-defined mass, predominantly hypoechoic and with internal vascularity on colour Doppler. On computerised tomography after administration of contrast media you can see a mass with intense homogeneous enhancement, similar to vascular structures [2]. On magnetic resonance imaging, the mass shows high signal on T2 and T2 FS sequences and demonstrates enhancement after intravenous administration of a paramagnetic agent. These are not cellular tumours and rarely exhibit restricted diffusion on DWI.
There are few reported cases of myopericytoma in deep locations. Although the definitive diagnosis is histological myopericytoma should be considered in the differential diagnosis of carotid space (Fig. 6) lesions, including paraganglioma and schwannoma. However, schwannoma may not enhance as intensely as myopericytoma and paraganglioma are classically located at the carotid bifurcation with characteristic splaying of internal and external carotid arteries, with a salt and pepper appearance in large lesions and intense enhancement following gadolinium.
Other diagnoses to consider would be hypervascular metastasis such as from papillary thyroid carcinoma, angioleiomyoma and haemangiopericytoma [3].
For diagnosis, ultrasound-guided core-needle biopsy may sometimes be required if hypervascular metastasis or Castleman disease (giant lymph node hyperplasia) is suspected, with bleeding being the major potential complication.
Most cases of myopericytoma behave in a benign fashion, but local
recurrence can occur [4]. Rarely metastases are seen in atypical and malignant
cases. In deeply located myopericytoma no case of recurrence after complete resection, or of metastatic disease has been reported.