Imaging Aspects of Palatal Torus in Cone Beam Computed Tomography and Magnetic Resonance: Case Report

Abstract

The torus palatinus is a unilocular or multilocular exostosis that occurs in the midline of the hard palate. It is considered a common clinical finding. Magnetic resonance imaging (MRI) is not commonly used in dentistry and descriptions of the torus by this imaging method are therefore rare in the literature. This case study reports on a female patient referred to the dentist to elucidate a bone enlargement detected by MRI, which was requested by the physician who accompanied the patient for migraine treatment. Additional routine dental imaging exams were performed for the planning of different treatments. Here is a description of the torus palatinus along with MRI in order to provide a complete representation of the clinical finding.

Introduction

The torus palatinus (TP) is a generally asymptomatic exostosis that commonly occurs in the midline of the hard palate. Its etiology is still not fully established (1, 2). Theories of the development of TP include genetic traits (2), environmental factors, or even a multifactorial theory (3) that comprises factors related to occlusal stress (4). Cantín et al. (5) emphasize that TP arises from tissues present in the palatine suture and can still occur in the maternal uterus.

Female patients during their fourth and fifth decades of life are most commonly affected (6). Clinically, TP is found in the midline of the posterior hard palate and manifests as a round and symmetrical, sometimes multilobulated, nodule (7), generally discovered on routine clinical examination (4).

Palatal and mandibular tori are microscopically characterized by lamellae of compact bone covered with a thin and poorly vascularized mucosa (6, 7). Larger specimens can have a center of cancellous bone and the only difference between the palatal torus and other exostoses is in its being developed at characteristic sites and in a symmetrical manner (7). Palatal tori are characterized by slow growth and the torus can reach a large size that requires surgical removal, for example, when representing an obstacle to prosthetic treatment (2, 7).

There are reports on complications related to TP, such as spontaneous exposure of a torus and osteonecrosis of a torus associated with the use of bisphosphonates, which require surgical or pharmacological treatment (8). On the other hand, the presence of tori can be advantageous since they can be sites of bone tissue collection for autogenous grafts in implant and periodontal surgery (8, 9).

Torus palatinus is frequently identified on computed tomography (CT) scans, where it appears as a bone protuberance with a density similar to that of compact bone (10). This complementary exam is needed in some cases, as stated in the report of Godinho et al. (8).

Magnetic resonance imaging (MRI) is not an imaging method of choice in these cases nor is it used for diverse dental planning. Reports of MRI of TP are therefore sparse in the literature. However, the description of MRI features of TP, in conjunction with its confirmation by an imaging method that is more familiar to the dentist such as CT, is important for dental and medical practice. This approach permits the differential diagnosis of this entity, which generally does not require intensive interventions, from other conditions that can mimic it. Within this context, this study provides a detailed description of the presence of TP of exacerbated dimensions on cone beam CT and MRI images.

Case report

A 44-year-old woman sought medical care because of recurrent episodes of migraine. An MRI scan of the skull was requested to help diagnose the case, which revealed a hyposignal in the region of the soft palate. The physician, who was unaware of this alteration, referred the patient to a dentist for diagnosis.

During anamnesis, the patient confirmed to be diabetic and hypertensive and reported significant nocturnal snoring. The patient was diagnosed with obstructive sleep apnea by an otorhinolaryngologist. Clinical examination showed a sessile nodule of firm consistency, which had the color of the adjacent mucosa (Figure 1a). Tomographic and radiographic examination revealed a concentric radiopaque image in the region of the hard palate, which measured approximately 2 cm in diameter. The T2-weighted MRI images of the skull showed a hypersignal throughout the lining of the left maxillary sinus compatible with mucosal thickening of the sinus and, surprisingly, an eminent hyposignal corresponding to pronounced bulging of the entire hard palate (Figure 2a and 2b).

Figure 1.

A) Initial clinical photograph of the jaws showing an exuberant torus palatinus. B) Periapical radiograph of the central incisors. Note the radiopaque image in the apical region of teeth 11 and 21. C) Periapical radiograph of the upper right canine.

Figure 2.

A) Magnetic resonance imaging in the frontal plane. B) Magnetic resonance imaging in the axial plane. C) Axial tomographic section. D) Coronal tomographic section. E) Sagittal tomographic section.

Imaging scans were performed for dental treatment planning. Imprecise areas of opacity with ill-defined borders and a bony aspect were observed on periapical radiographs of the upper anterior teeth, which occupied the region corresponding to the nasal fossae (Figure 1b and 1c). Panoramic radiography showed an extensive radiopaque convexity area in the region of the hard palate, which extended bilaterally to the molar area and had the appearance of cancellous bone tissue. Cone beam CT was performed using an ICAT Next Generation dental scanner (Imaging Science International, Hatfield, PA, USA), with a field of view of 16 x 13 cm comprising the middle third of the face. Axial, coronal and sagittal sections were obtained, which revealed an extensive hyper dense lobulated bilateral mass with the density of bone tissue that caused bulging of the entire hard palate (Figure 2c, 2d and 2e).

The final diagnosis was TP. The patient received detailed information about the anatomical variation and returned to medical treatment for her migraine.

Discussion

Gorsky et al. (3) studied the prevalence of TP in a population of 1,002 Israeli Jews. The prevalence of TP was 21% in the entire sample and a higher prevalence was observed among women (24.9%) compared to men (16.45%), without significant differences between age groups (≤ 21 years and > 21 years). The most common location was near the molar area. The prevalence of tori larger than 2.0 cm was higher among older subjects. Al-Bayaty et al. (2) reported an average age at the onset of TP of 30.7 years. However, Beena (11) reported the case of an 18-month-old boy with TP, in which he concluded that torus can adversely affect some oral functions such as speech, especially during childhood.

One study demonstrated a high incidence of tori among families, suggesting a dominant autosomal inheritance (12). Pechenkina et al. (13) studied exostosis formation and found out that exostosis was unusually common on the Neolithic skulls from China. They concluded that the formation of exostoses is a complex process the etiology of which can be any trauma or inflammation of gingival tissue. Severe occlusal stress is the most common environmental factor, which can lead to the development of exostosis when the individual has a genetic predisposition. However, this hypothesis is not well founded since tori are located distant from dental structures, as observed in the present case.

Morrison and Tamimi (14) studied the patients with tori and those without oral tori and found out that tooth wear is related to parafunctional habits in patients with tori. A correlation was also observed between the presence of a torus and hypothyroidism. Age, gender, smoking, hypertension, periodontal disease, diabetes or depression did not differ between groups. Respiratory problems, including apnea as reported during medical history taking for the present case, were also correlated with the presence of tori. Palm et al. (15) evaluated the relationship between the presence of torus mandibularis and obstructive sleep apnea and found no association between the prevalence of tori and snoring or different degrees of apnea. However, smaller tori tended to be present in more severe degrees of apnea, disagreeing with the hypothesis of the authors who have stated that larger tori interfere with sleep disorders when air is blocked from entering into the lungs. Furthermore, the patients with larger tori treated with a mandibular advancement device had significantly better success rates than those with smaller tori. The hypothesis was that larger tori contribute to tongue positioning and subsequently reduce sleep apnea symptoms. In our case, the presence of the torus was not correlated with snoring or apnea of the patient. Studies associating TP with sleep disorders are sparse.

The differential diagnosis of tori includes osteomas found in patients with Gardner syndrome. However, these osteomas are generally numerous and asymmetrical, are more common in the mandible, and are associated with dental impaction and syndrome-related odontoma (1). This hypothesis was ruled out in the present case, since the patient did not exhibit any other alteration. Torus palatinus can also be found in patients with Worth syndrome, a rare dominant autosomal disease, known as hyperostosis corticalis generalized congenita. This rare disease is characterized by increased bone density, the presence of bone protuberances (TP) in the palate, and thickening of various long bones (16).

The importance of a correct diagnosis is related to the choice of treatment. Tori can persist for a long period and their surgical excision may become necessary. Different types of safe surgery are being investigated for these cases. In a study using an Er:Yag laser, the instrument promoted good remodeling of the surgical wound, decontamination and biostimulation despite an increased length of surgery (17). Computed tomography is widely used for the diagnosis of specific pathological conditions or observation of anatomical structures, since it provides a three-dimensional view and transverse images and permits to visualize details when compared to panoramic or periapical radiography (10). Tomography scans permit better evaluation of these anatomical variations and demonstrate their relationship with adjacent structures and the composition of medullary and cortical bone (12). However, in most cases, TP is also an incidental finding on CT. Ruprecht et al. (18) investigated mandibular tori by relating their intraoral radiographic appearance to their corresponding appearance in dissected skulls and found that tori smaller than 3 mm are very difficult or impossible to detect radiographically.

The description of tori by MRI is rare in the literature. Platzek et al. (19) described the MRI features of a case of mandibular torus, including low signal intensity as it consists of compact bone. Smaller tori are difficult to identify on MRI scans and their detection is impaired in the presence of metallic artifacts. This was not the case in the present study, in which the torus and its relationship with adjacent structures were easily identified. However, in most cases, this anatomical variation does not require additional diagnostic methods. Computer tomography is needed for dental planning and to make a correct diagnosis. Also, MRI is used for medical diagnostic purposes, apart from situations in which clinical alterations occur in the torus. Generally, its clinical features are sufficient for the diagnosis and imaging findings are specific and should be part of medical and dental knowledge. Case reports are therefore important, especially for professionals involved in the diagnosis of head and neck lesions who are not familiar with this entity, in order to avoid unnecessary procedures.

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