Clinical Investigations
Prognostic factors of nasopharynx tumors investigated by MR imaging and the value of MR imaging in the newly published TNM staging

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Abstract

Purpose: To examine the usefulness of MR imaging for predicting local control of nasopharyngeal carcinoma (NPC) and the value of MR imaging in the newly published fifth edition of the TNM classification.

Methods and Materials: We studied 29 patients with NPC with MR imaging and CT before and after treatment. Staging was done according to the fourth and newly published fifth editions of the International Union Against Cancer (UICC) staging system. The radiotherapy protocol was designed to deliver 66 to 68 Gy to the primary tumor and clinically involved nodes.

Results: MR proved better than CT at identifying obliteration of the pharyngobasilar fascia, invasion of the sinus of Morgagni, through which the cartilaginous portion of the eustachian tube and the levator veli palatini muscle pass, invasion of the skull base, and metastases to lymph nodes in the carotid and retropharyngeal spaces. All seven patients without invasion of the pharyngobasilar fascia had local control. The local control rates of patients with invasion of the skull base were not good (60 to 73%). There was no apparent relationship between tumor volume determined by T1-weighted MR images and local control when the tumor volume was more than 20 cc. The newly published N staging system appears to successfully identify the high-risk group for distant metastasis as N3. In our series, four of five patients with N3 disease developed distant metastases.

Conclusion: Deep infiltration of the tumor is a more important prognostic factor in NPC than tumor volume. Since the newly published T staging system requires a search for tumor invasion into soft tissue such as parapharyngeal space and bony structures, MR imaging may be indispensable for the newly published NPC staging system.

Introduction

A proper staging system is needed for all tumors of all possible sites, in order to choose treatment modalities, assign prognosis, and exchange information among institutions. The fourth edition of the TNM classification proposed by the Union Internationale Contre le Cancer (International Union Against Cancer; UICC) (1) has been used for the staging of nasopharyngeal carcinoma (NPC). Computed tomographic (CT) scanning is very useful in the diagnosis and evaluation of tumors of the nasopharynx, and is widely used. However, CT findings are not always reflected in the fourth edition of the TNM classification of NPC, because this classification system does not consider the extent of depth of tumor infiltration.

The fifth edition of the TNM staging system was published in 1997 by the UICC (2), and this new staging system for NPC represents substantial change from the fourth edition. Within this new system, radiologic imaging, such as CT and magnetic resonance (MR) imaging, plays an important role because in the diagnosis of T2, T3, and T4 tumors, such imaging is essential for an evaluation of the invasion of bony structures, the paranasal sinuses, the intracranium, the infratemporal fossa, and the orbit.

MR imaging has excellent soft tissue contrast resolution and multiplanar imaging capability (3). MR imaging has recently proven to be a valuable diagnostic tool in the diagnosis of lesions of the nasopharynx. However, the exact role of MR imaging in the T-staging of NPC has not well been established.

In the present study, we examined the value of MR imaging for predicting both local control and distant metastases. We also compared the prognostic ability of the newly published fifth edition of the TNM classification of NPC with the fourth edition.

Section snippets

Methods and materials

From January 1988 to September 1995, 29 patients with NPC were studied with MR imaging and CT before and after treatment: 20 patients were male and 9 were female, ranging in age from 15 to 78 years (mean age, 50 years). All cases were biopsy-proven squamous cell carcinoma. Only one patient had distant metastases at presentation and he was treated with the same radiotherapy as the others and was included in the analysis for local control.

The radiotherapy protocol was designed to deliver 66 to 68

Staging

A detailed analysis of the results obtained in the staging is reported in Table 2. Obliteration of fat planes in the parapharyngeal space was seen in all patients. However, it was impossible to detect obliteration of the pharyngobasilar fascia with CT. It was also difficult to identify invasion of the sinus of Morgagni with CT, but MR imaging identified it much more clearly. MR imaging proved better than CT at identifying metastases to lymph nodes in the carotid space and the retropharyngeal

Discussion

Since the introduction of CT use, there has been a dramatic change in the results of T and N staging of NPC. Because CT detects subtle bone destruction, more patients have been classified as T4, based on the fourth edition of the UICC staging system. However, it is not conceivable that T4 tumors staged by clinical findings alone or by CT or MR imaging have the same local prognosis after radiation therapy. Improved 5-year local failure-free rates reported in the international literature 4, 5 in

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