Review
CT and MR imaging findings of palatal tumors

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Abstract

Palatal tumors commonly arise from the minor salivary glands, and benign tumors account for approximately half of all minor salivary gland tumors. Minor salivary gland tumors have an affinity for the posterior hard palate and soft palate and virtually never arise in the midline, probably because of the distribution of palatal salivary glands. The majority of benign salivary gland tumors of the palate are pleomorphic adenomas, while the most common malignant salivary gland tumor is adenoid cystic carcinoma, followed by mucoepidermoid carcinoma, adenocarcinoma, and polymorphous low-grade adenocarcinoma. Epithelial tumors frequently arise from the soft palate. The majority of benign epithelial tumors of the palate are papillomas, while most malignant epithelial tumors are squamous cell carcinomas. Various types of mesenchymal tumors, including fibromas, lipomas, schwannomas, neurofibromas, hemangiomas, and lymphangiomas, also involve the palate. This article describes the CT and MR findings of benign and malignant palatal tumors.

Introduction

The hard palate is one of the anatomical subdivisions of the oral cavity. It comprises the anterior two-thirds of the palate and separates the oral cavity from the nasal cavity. It is formed by the palatine process of the maxilla and the horizontal plate of the palatine bone, which is covered by a mucous membrane, and hundreds of minor salivary glands are located between the mucosal surface and the underlying bone.

The soft palate is one of the anatomical subdivisions of the oropharynx. It comprises the posterior third of the palate and separates the oropharynx from the nasopharynx. It is formed by connective tissue and muscle fibers, mainly the glossopalatine and pharyngopalatine muscles, without underlying bone. The soft palate is covered by squamous mucosa and contains a smaller number of minor salivary glands compared with the hard palate. It is very flexible during speaking and swallowing.

Minor salivary glands usually located in the oral cavity, include the labial, buccal, molar, lingual, and palatine glands. The palatine glands form a thick submucosal layer in the soft palate and a thin submucosal layer in the hard palate, but they are absent in the region of the incisive fossa and the anterior part of the palatine raphe. The palatine glands are primarily mucous secreting glands.

The sensory supply to the palate is derived mainly from branches of the maxillary nerve via the pterygopalatine ganglion in the pterygopalatine fossa. The greater palatine nerve exits to the oral cavity via the greater palatine foramen, whereas the lesser palatine nerve via the lesser palatine foramen (Fig. 1). The nasopalatine nerve passes along the nasal septum in the nasal cavity, and into palatal mucosa through the incisive foramen. The greater palatine nerve supplies the gums, the mucosa and glands of the hard palate, and communicates in front with the nasopalatine nerve, whereas the lesser palatine nerve supplies the mucosa and glands of the soft palate and uvula. A small area behind the incisor teeth is supplied by the nasopalatine nerves.

From the pterygomaxillary junction to the pterygopalatine fossa region, the maxillary artery was usually branched into 5 arteries in the following order: posterior superior alveolar artery, infraorbital artery, artery of the pterygoid canal, descending palatine artery, and sphenopalatine artery. The descending palatine artery branches into the greater palatine artery and lesser palatine artery. The greater palatine artery descends through the greater palatine foramen and supplies the hard palate, anastomosing through the incisive foramen with the posterior septal branches of sphenopalatine artery that supplies the nasal cavity. The lesser palatine artery descends through the lesser palatine foramen and supplies the soft palate and the palatine tonsils, anastomosing with the ascending palatine artery that branches off from the facial artery.

Benign and malignant palatal tumors are usually asymptomatic masses that are occasionally associated with a low level of discomfort. Salivary gland tumors of the palate usually appear as slow-growing, well-circumscribed, dome-shaped, smooth-surfaced, nonmovable swellings. Pain or ulceration is occasionally observed. Adjacent bone invasion, perineural extension, and sinonasal involvement are commonly observed with palatal malignancies [1]. Tumor size, histological tumor grade, and presence of lymph node metastasis at the time of initial diagnosis are associated prognostic factors for palatal malignancies [2], [3].

Preoperatively, fine-needle aspiration cytology plays a definitive role in revealing the epithelial, myoepithelial, and stromal components of tumors [4]. CT and MR imaging are usually performed to assess the extent of the tumor, including bone erosion or destruction, soft tissue involvement, and perineural spread. This review aims to illustrate the CT and MR imaging findings of benign and malignant palatal tumors.

Section snippets

Cross-sectional imaging

CT and MR imaging are the most frequently used imaging modalities. CT is useful for evaluating adjacent bone erosion or destruction, and coronal CT images should be obtained by multiplanar reconstruction (MPR). Metallic artifacts are quite common in CT images of patients who have metallic dental implants or filling materials, whereas most dental metallic materials usually cause mild distortions to the local magnetic field. Moreover, MR imaging provides excellent soft-tissue contrast that is

Staging of malignant palatal tumors

Malignancies of hard or soft palate origin are known to spread perineurally along the palatine branches of the maxillary nerve. The characteristic imaging findings of perineural spread into greater or lesser palatine foramen include asymmetric enlargement or destruction on CT images, obliteration of fat plane on T1-weighted images, or the enlarged nerves with abnormal enhancement on contrast-enhanced T1-weighted fat-suppressed MR images.

Malignancies of soft palate occasionally metastasise to

Pleomorphic adenoma

Pleomorphic adenoma is the most common type of salivary gland tumor of the palate. Other sites of occurrence in the oral cavity include the lips, buccal mucosa, tongue, floor of the mouth, tonsils, pharynx, and retromolar area [10]. In the palate, it is commonly located lateral to the midline of the posterior hard palate. These tumors frequently present as painless, firm or rubbery, slow-growing, well-delineated masses that are covered with normal mucous membranes, although mucosal ulcerations

Adenoid cystic carcinoma

Adenoid cystic carcinoma is the most common salivary gland malignancy in the palate. These tumors typically present as indurated masses in the lateral to middle area of the hard palate and may be ulcerated. Persistent pain usually occurs before any noticeable swelling. Adenoid cystic carcinomas can be classified into three distinct histopathological patterns: tubular, cribriform, and solid [34]. Palatal lesions are known to spread perineurally along the palatine branches of the maxillary nerve

Conclusions

In conclusion, the differential diagnosis of palatal tumors can present a challenging task for radiologists. However, an understanding of benign and malignant tumors that affect the hard and soft palate allows radiologists to make correct diagnoses, and also directs physicians to appropriate clinical diagnoses and treatments.

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