Primary Chordoma of the Nasopharynx: A Rare Case Report and Review of the Literatures

Primary chordoma of the nasopharynx is an extremely rare malignant tumor of notochordal origin in the extra-osseous axial skeleton. It presents as a soft tissue mass without involvement of the skull base bone (clivus) and may mimic other lesions of the nasopharynx. A 26-year-old male patient is presented with nasal obstruction and congestion for the last 3 years. Physical and radiological examination revealed a mass in the naso-oropharyngeal region. It was suspected to be a cystic mass or abscess on radiological imaging. However, histopathological examination revealed a chordoma. We review all 20 cases of primary nasopharyngeal chordoma reported previously in the literature. Nasopharyngeal chordoma should be considered in the differential diagnosis of nasopharyngeal mass due to its unspecific appearance on clinical and radiology examination.


Introduction
Chordoma is a rare malignant bone tumor that occurs in any site along the course of embryogenic notochord and typically in the axial skeleton [1]. It affects males twice compared to females, and the age range is 40-60 years [1,2]. e topographic distribution of chordoma includes sacrococcygeal (50%), cranio-cervical/spheno-occipital (35%), and thoraco-lumbar spine (15%). Cranio-cervical chordomas most o en involve the dorsum sellae, the clivus, and rarely the nasopharynx [2]. Unusual locations had been reported including the mandible and the maxilla (dental chordoma), some also with nasal and paranasal presentations [3].
Histologically, the hallmark of chordoma is the presence of large physaliphorous cells (Greek: physalis: bubbles) with vesicular nuclei embedded in a homogenous, intercellular substance. e vacuoles contain either mucinous substance or glycogen. e intercellular substance is considered as partly the result of cell secretion and in part of products of cell degeneration [4].
Chordoma is categorized into 3 types: Classical or conventional chordoma, which is rich in physaliphorous cells, and is the most frequent type of chordoma; chondroid chordoma, resembling both chordoma and chondrosarcoma; and dedifferentiated chordoma featuring sarcomatous areas which are comprised of spindle-shaped and polygonal cells, and is the most aggressive type of chordoma [5].
Immunohistochemically, the notochordal cells strongly express cytokeratin but weakly vimentin in the earlier developmental stages of the foetus. In later developmental stages, it shows distinct increase in vimentin expression and a slight decrease in cytokeratin expression [6]. Chordoma may also express epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), S100 protein, alpha 1-antichymotrypsin, and lysozyme [7]. Brachyury had been proposed as the most specific diagnostic marker of chordoma's neoplastic cells since it is a transcription factor which is required for notochord development during embryogenesis [8].
Herein we report a case of primary chordoma of the nasopharynx, its characteristics, and a review of previously reported cases.

Case Presentation
A 26-year-old man was admitted to the ear, nose, and throat department of our hospital with nasal obstruction and congestion of 3 years duration. ere was no history of headache, epistaxis, visual changes, or cranial nerve palsy/ paresis.
Physical examination showed a mass in naso-oropharyngeal region with anterior displacement of the uvula. Radiological examination by axial, coronal, and sagittal MSCT with and without contrast confirmed the presence of a roundlarge lobulated mass in naso-oropharyngeal region, approximately 5 × 6 cm with well-defined margin without involvement of the clivus (Figure 1). It was interpreted as a naso-oropharyngeal cystic mass, possibly a naso-oropharyngeal abscess. Chest X-ray was unremarkable. Laboratory workup revealed that all haematological and biochemical parameters were within normal limits.
Biopsies were taken from different parts of the mass (right and le nasopharynx and oropharynx) but they were superficial and did not reach the tumor itself. Histologically, they showed nonspecific chronic inflammation. e patient was treated with antibiotic and anti-inflammatory drugs, without any clinical improvement.
A deep biopsy from the mass was eventually obtained, and it revealed a chordoma of the nasopharynx. e patient underwent surgery to excise the mass with trans-palatal rhinotomy approach, under general anaesthesia. Approximately 30 cc of fragmented tissue was received. Macroscopically, the tumor tissue was firm and lobulated, some was covered by brownish white mucosa. Microscopic examination showed cords and lobules of physaliphorous cells embedded within extensive myxoid stroma, separated by fibrous septa. Some of tumor cells already invaded adjacent skeletal muscle. e physaliphorous cells were variable in size, with abundant eosinophilic to clear cytoplasm, some were vacuolated, with prominent vesicular nuclei. Other tumor cells were small with pyknotic nuclei. Mitotic figures were inconspicuous ( Figure 2). e immunohistochemical studies revealed positive cytoplasmic staining for cytokeratin and vimentin. Meanwhile, expression of S100 was slightly weaker (Figure 3). Immunostaining of brachyury was not performed since it was not available in any of the pathology laboratories in our country. A er surgery, the patient showed excellent recovery with no other complication. e patient had been closely followed up at the ENT outpatient clinic.

Discussion
Chordoma is a rare malignant bone tumor, primarily involving both ends of the axial skeleton, and arise from the remnant of the notochord. It was first described by Virchow in 1857 as a tumor made up of vacuolated or physaliphorous cells derived from rests of embryonic notochord along the midline central nervous system axis [9]. e notochord is a rod-like aggregate of cells extending the entire length of the embryo on the midline, ventral to the developing neural tube. e embryonic notochord degenerates early in fetal development a er being surrounded by sclerotome mesenchymal cells and remains as the nucleus pulposus within intervertebral disc. However, in some cases residual notochord cells remain outside the inter-vertebral disc and may become neoplastic [10].
Primary nasopharyngeal chordoma arises in the extraosseous nasopharyngeal so tissues and may or may not have a smaller intraosseous component along the course of the medial basal canal. e medial basal canal is considered the cephalad exit tract of the notochord as it moves from its intraclival location ventrally into the midline nasopharyngeal so tissues [3]. Chordomas arising from the skull base/clivus with extension into the nasopharynx area are excluded in the list of primary nasopharyngeal chordomas [1]. ey are preferably diagnosed as clival chordomas presenting as nasopharyngeal mass [11,12].
Primary nasopharyngeal chordoma commonly occurs in young adults with an average age of 39.6 years, ranging from 8 to 80 years. It affects males (57.1%) more than females (42.8%) with a male to female ratio of 1.3 : 1. e main clinical presentation is nasal obstruction, reported in 16 cases (76.2%). Other symptoms include hearing impairment, headache, difficulty in swallowing, dryness of the mouth, nasal bleeding, diplopia, numbness, dropping of upper eye lid, difficulty in breathing, and nasal speech. Almost all patients with primary nasopharyngeal chordoma show unremarkable laboratory findings and normal general physical examination. e tumor size ranged from 2.5 to 8.2 cm and all were lobulated. Chondroid chordoma was found in a single case with progressive manifestation within 3 months prior to diagnosis, and chondrosarcoma cannot be excluded in the differential diagnosis. Twenty cases were identified as classical chordoma (95.2%) and 6 cases (28.6%) showed slow growing tumors, with clinical manifestation observed within 6 months up to 5 years prior to the diagnosis. 5 cases had no further information regarding the onset of their clinical manifestation.
Histopathologically, 20 cases (including the current case) were classical chordomas showing numerous physaliphorous cells arranged in cord or lobules with myxoid stroma separated by fibrous tissue, meanwhile 1 case was chondroid variant, showing chondroid differentiation resembling chondrosarcoma [5]. Radiologically, classical and chondroid chordoma can be misdiagnosed with cyst, abscess, nasopharyngeal angiofibroma, or even nasopharyngeal carcinoma. Clinically, unlike malignant lesion, benign lesion do not progress in size in a short time, or invade or destroy the surrounding tissues. Cystic lesions are identified by single or multiple spaces lined with cuboidal or flattened epithelial cells [20]. Nasopharyngeal abscess formation is characterized by prominent necrotic area, infiltrated by numerous inflammation cells, specially leucocytes [21]. Angiofibroma showed proliferation of fibroblasts along with numerous blood vessels [22]. Lastly, nasopharyngeal carcinoma is characterized by islands of epithelial cells which consisted of round, oval to spindle atypical cells, infiltrating to surrounding area [23]. Up to now, dedifferentiated type of primary nasopharyngeal chordoma has not been reported yet.
is case report was interesting on several counts. We experienced some difficulties during the pre-operative diagnosis due to the nonspecific features of chordoma on clinical and radiological examinations. Moreover, particular location of the tumor was difficult to be reached and biopsied. ose factors resulted in delayed accurate diagnosis. Because of the location in nasopharynx region, the differential diagnosis of chordoma should be made from other nasopharyngeal masses. Although CT and MRI features are nonspecific, they may be suggestive of chordoma including midline location, expansible or lobular so tissue mass with well-defined margin. Other nasopharyngeal malignancies may destroy clival bone but do not demonstrate this midline tract. CT is ideal for evaluating