Case
We present the case of a 22-year-old male who presented with a 10-year history of gradual right-sided hemifacial weakness, later developing a mass at the right preauricular area. The gradual enlargement of the mass prompted consultation and subsequent management in our tertiary government hospital.
On physical examination there was a 4×7 cm non-hard, slightly movable mass on the right inferior preauricular area (Fig. 1). Testing for actions of the facial muscles, the patient demonstrated right-sided weakness upon raising the eyebrows, closing the eyes, blowing out the cheeks and smiling (Fig. 2).
Ultrasonography showed a right parotid mass located inferolaterally to the gland, measuring 34.3×25.5×65.1 mm. The mass exhibited heterogenous echopattern containing hyperechoic and anechoic areas. It was hypovascular, with solid and cystic areas, and microcalcifications (Fig. 3).
Ultrasound-guided fine needle aspiration of the right parotid gland revealed a salivary gland neoplasm of uncertain malignant potential and cellular basaloid neoplasm.
Considering the presence of facial paralysis and the preauricular mass, our clinical diagnosis was a parotid malignancy. Preparation for surgery included discussion of the extent of surgical resection with nerve sacrifice, planning for facial reanimation and counselling of the patient for possible permanent facial paralysis. A multidisciplinary team of surgeons from surgical oncology and plastic surgery worked together during the operation.
The patient underwent total parotidectomy performed by the surgical oncology team. During resection, the tumor was noted to arise from the deep lobe and under the facial nerve abutting the cervical and mandibular branches (Fig. 4A). The mass was dissected off from the nerve without breaking its capsule (Fig. 4B).
The plastic surgery team then proceeded to do a minimal access cranial suspension lift and supra brow lift to address the right sided facial drooping.
Gross examination of the resected parotid specimen revealed a 7.5×4.3×3.2 cm parotid gland with a 3.7×3.4×2.9 cm, non-hard, well-encapsulated mass at the inferior portion (Fig. 5A). Cut section of the inferiorly located nodule revealed a 3.7×3.2×2.9 cm mass which was fleshy with cystic areas containing dark brown fluid (Fig. 5).
The patient’s post-operative hospital stay was unremarkable, and he was discharged on the third post-operative day. However, his symptoms of right-sided facial weakness persisted.
Histopathologic examination of the resected specimen revealed a spindle cell neoplasm described as a solid cluster of pleomorphic spindle cells arrange in a storiform architecture, invading into the surrounding fibrous capsule (Figs. 6 and 7). Vesicular nuclei and prominent nucleoli admixed with numerous mitotic figures were also noted within the specimen. All lines of resection were negative.
Differential diagnoses at this stage included myoepithelial carcinoma, MPNST, and hemangiopericytoma. Further immunohistochemical staining with S-100, vimentin, p63, epithelial membrane antigen (EMA), smooth muscle actin (SMA), CD34, and cytokeratin allowed us to narrow down our diagnosis. Positive staining for S-100 and vimentin confirmed our diagnosis of MPNST (Figs. 8 and 9). There was marked improvement in his facial asymmetry as noted 12 months postoperatively (Fig. 10). He was advised to undergo radiotherapy but refused further treatment and follow up.
Discussion
Mesenchymal tumors represent approximately 2% to 5% of all salivary gland tumors, with over 95% of all tumors involving the major salivary glands. Malignant tumors occur less frequently with the ratio of benign to malignant tumors at 2.4:1 up to 18:1 [4]. MPNSTs, tumors that arise from nerve sheaths of peripheral nerves, represent a small fraction of all sarcomas at about 2%. MPNSTs most commonly involve the nerve roots and bundles in the pelvis and extremities, with notable involvement of the sciatic nerve [2]. MPNSTs of the head and neck are very rare, with tumors involving the parotid gland even rarer still. Parotid gland MPNSTs comprised only 4 out of 142 head and neck MPNSTs in a review of literature spanning 13 years from 1990 to 2003 [3]. According to this study, the usual clinical presentation of MPNST is that almost half arise in the context of neurofibromatosis (NF1) syndrome, usually in association with pre-existing plexiform neurofibromas which was not noted in our patient. MPNST present as rapidly enlarging mass which could either be painful or can cause local neurological symptoms such as weakness or paresthesias [3] as manifested by our patient.
A sarcoma is assumed to be MPNST if one of the following 3 criteria are met: 1) tumor arises from a peripheral nerve; 2) tumor arises from a pre-existing benign nerve sheath tumor or neurofibroma; and 3) tumor displaying constellation of histological features of Schwann cell differentiation [4]. In our patient, the tumor appears to arise from the facial nerve deep within the substance of the parotid.
Immunohistochemical studies were essential in confirming the diagnosis of MPNST. S-100 protein was the most widely used antigen for neural differentiation [2], and approximately 50%-90% of MPNSTs are positive for S-100 protein [5]. Vimentin was also strongly positive in all reported cases of MPNST [2]. In our patient, the tumor stained positively for S-100 protein and vimentin on the cells of interest. The tumor did not stain positively for EMA, CD34 or cytokeratin marking the tumor as less likely of epithelial origin. Negative staining for SMA likewise ruled out hemangiopericytoma as a possible differential.
The prognosis of MPNST is generally poor. The 5-year survival rate varies from 40% to 50% [2]. The mainstay of treatment has been complete surgical resection. In our patient, the margins of resection were negative, however due to the rarity of these tumors further studies are needed to fully understand the extent of optimal surgical management of these tumors [6]. High quality studies evaluating adjuvant treatment with chemotherapy [7] and radiotherapy [8] likewise have not yielded promising results. MPNST is highly chemotherapy-resistant and adjuvant chemotherapy is usually only reserved for advanced, unresectable disease or metastatic disease however even in these populations the benefits are limited [7]. A comprehensive multidisciplinary approach to the management of the disease is necessary for a chance at a better outcome.
In conclusion, we present a rare case of MPNST arising from the parotid gland in a young male patient. Review of previous literature revealed that MPNST arising from the parotid gland is very rare and diagnosis relies heavily on confirmatory testing via immunohistochemistry. Prognosis of MPNST is generally poor and treatment relies on achieving complete resection of the tumor. After complete resection, reconstructive procedures can be considered to improve function and cosmesis. Options for adjuvant treatment are limited and a multidisciplinary approach to the patient is recommended to afford the best outcomes.