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Neuroradiology Case of the Week

Case 441

September 2009

Ashwani K. Sharma, MD, Virendra Kumar, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 47-year-old male with a significant history of having been treated for sleep apnea syndrome and nasal obstruction for one year. For the past six months he had decreased hearing on the left side and a history of headaches with increased frequency and visual disturbance.

Imaging Findings: Left sided nasopharyngeal mass is noted but does cross the midline and fills the left fossa of Rosenmüller. The lesion measures 5.0 cm in superior/inferior dimension, 4.4 cm in transverse dimension and 2.2 cm in AP dimension. There is superior extension of the lesion to the skull base at the clivus without apparent extension into the skull base.

Additionally, the left foramen ovale is well visualized separate from this lesion without evidence of abnormal perineural enhancement. The lesion inferiorly extends to the superior aspect of the oropharynx, and immediately abuts the longus colli muscles posteriorly without evidence of definitive infiltration. Along the left border of this lesion, there is mass effect upon the left masticator and carotid spaces. The separating fat planes are preserved at these locations.

Diagnosis: Nasopharyngeal carcinoma

Discussion: The word "nasopharynx" is a combination of part Latin and part Greek words. Naso is the Latin word "nasus" meaning nose. "Pharynx" is the Greek word for throat. The Greco-Roman term "nasopharynx" was coined in 1877.
     Nasopharyngeal carcinoma (NPC) is a rare tumor arising from the epithelium of the nasopharynx. Most common in patients between 40 and 60 years old, with bimodal age peaks occurring in adolescence and in elderly people (aged 50-60 years). In the United States, nasopharyngeal carcinoma accounts for approximately 0.25% of all malignancies, and there is an age peak among African Americans from 10 to 19 years old [2]. In Southeast Asia, nasopharyngeal cancers account for approximately 15–18% of all malignancies, but childhood tumors are rare [2].
     NPC is a multifactorial disease that may be the result of interactions involving race, genetics, and environment. Regardless of histologic subtype, almost 100% of cases of nasopharyngeal cancer have the Epstein-Barr virus–encoded RNA (nontranslated RNA that is not associated with protein production). Familial clusters have been reported, and there is a genetic susceptibility with HLA-A2, HLA-B17, HLA-w46, and HLA-Bsin2 [1].
     NPC rarely comes to medical attention before it has spread to regional lymph nodes. Other presentations include nasal symptoms (like congestion, nasal discharge, bleeding), changes in hearing, and cranial nerve palsies. NPC tend to spread along the path of least resistance, like extension along the muscle bundles, neurovascular structures, fascial planes, and within mucosa and submucosa. Superiorly it may directly invade the skull base (most common sites of intrusion are the region of the petroclival fissure and the foramen lacerum). Perineural infiltration occurs along the branches of 5th nerve up to the skull base and intracranially (cavernous sinus). Tumor may extend anteriorly to involve the pterygopalatine fossa, posterior aspect of the nasal cavity, and tonsillar fossa. Posteriorly tumor may extend to the posterior compartment of the parapharyngeal space and thus involve cranial nerves (9-12), and sympathetic chain. Late cases may invade the prevertebral muscles.
     Eighty-two percent of nasopharyngeal cancers arise in the posterolateral recess of the pharyngeal wall (usually in the Rosenmüller's fossa), and 12% arise in the midline. Between 60% and 72% of patients present with cervical nodal metastasis; however, there is no direct relationship between tumor size and the presence of cervical nodal metastases. Advanced disease is considered to be present when there are findings of hearing loss, otalgia, or headache or evidence of cranial nerve involvement (10–12%) [1]
     Perineural tumor spread primarily occurs after tumor has invaded into the pterygopalatine fossa, the foramen ovale, and the hypoglossal canal. Further extension of tumor can involve the orbit, cavernous sinus, and even the brain stem, all with a concomitantly worse prognosis. Signs of perineural spread include thickening and enhancement of the affected nerves, lateral bulging of cavernous sinus, foraminal enlargement on CT, atrophy of muscles of mastication and obliteration of the normal fat in the pterygopalatine fossa.
     In 12% of cases, the nasopharyngeal cancer arises in the midline nasopharynx. It can be predominantly submucosal or present as mucosal thickening. Clinical evaluation of these patients may be easily confused with benign lesions such as a Thornwaldt cyst or a retention cyst.

Imaging Features: Focal or diffuse thickening of the nasopharyngeal mucosa and cervical lymphadenopathy are the most common presentations of nasopharyngeal carcinomas
The lesions mostly show hypointense to isointense signal intensity (relative to muscles) on T1-weighted images,slightly hyperintense on T2-weighted images, and show moderate to intense enhancement on contrast-enhanced sequences. Because of its locally aggressive nature, nasopharyngeal cancer can penetrate the tough pharyngobasilar fascia extending from the top of the constrictor pharyngis superior muscle to the skull base. The tumor can also directly breach the foramen of Morgagni in the pharyngobasilar fascia, a gap in the upper ventral pharyngobasilar fascia through which the eustachian tube and the levator veli palatini muscle extend. Nasopharyngeal cancer can also violate the buccopharyngeal fascia as it encircles the pharyngeal muscles. Once through this fascia, tumor can rapidly spread to the parapharyngeal, masticator, and retropharyngeal spaces.
     Imaging of all the cervical lymph nodes is essential for staging. The retropharyngeal lymph nodes are usually the first nodes to be affected.

     At presentation, 5–11% of patients will have distant metastases, and during the course of treatment, 50–60% of patients will develop metastases. Almost 80% of metastases occur within 18 months after symptoms first appear, and after the detection of distant metastases, the mean survival is approximately 6 months [1]. Radiation therapy is the mainstay of treatment, with chemotherapy used in advanced cases. Concurrent cisplatin, 5-fluorouracil, and radiotherapy have been shown to improve survival.

References:

1. Chong VF, Zhou JY, Khoo JB, Chan KL, Huang J. Correlation between MR imaging-derived nasopharyngeal carcinoma tumor volume and TNM system. Int J Radiat Oncol Biol Phys. 2006 Jan 1;64(1):72-6. PMID: 16271442 [PubMed]
2. Kalogera-Fountzila A, Karanikolas D, Katodritis N, Samantas E, Sarafopoulos A, Ikonomou I, Zamboglou N, Tselis N, Dimitriadis AS, Fountzilas G; AJCC (American Joint Committee on Cancer). Prognostic factors and significance of the revised 6th edition of the AJCC classification in patients with locally advanced nasopharyngeal carcinoma. Strahlenther Onkol. 2006 Aug;182(8):458-66. PMID: 16896592 [PubMed]
3. Sobin LH, Wittekind C, eds. UICC TNM Classification of Malignant Tumors. 6th ed., New York: Wiley-Liss, 2002.
4. Som PM, Curtin HD. Head and Neck Imaging. 4th ed., Mosby, 2003.
5. Chin SC, Fatterpekar G, Chen CY, Som PM. MR imaging of diverse manifestations of nasopharyngeal carcinomas. AJR Am J Roentgenol. 2003 Jun;180(6):1715-22. PMID: 12760949 [PubMed]
6. Slootweg PJ, Richardson M. Squamous cell carcinoma of the upper aerodigestive system. In: Gnepp DR, ed. Diagnostic Surgical Pathology of the Head and Neck. Philadephia: WB Saunders, 2001:19–29.
7. Fu YS, Perzin KH. Pathology of the nasal cavity, paranasal sinuses, and nasopharynx. In: Fu YS, Wenig BM, Abemayor E, Wenig BL, eds. Head and Neck Pathology with Clinical Correlations. New York: Churchill Livingstone, 2001:137 –230.