BENIGN MANDIBULAR LESIONS: a PICTORIAL REVIEW LESÕES BENIGNAS DA MANDÍBULA: UMA REVISÃO PICTÓRICA Francisco Rego Costa1, Cátia Esteves1, Maria Teresa Bacelar2
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ACTA RADIOLÓGICA PORTUGUESA Maio-Agosto 2016 nº 108 Volume XXVIII 25-34 Artigo de Revisão / Review Article BENIGN MANDIBULAR LESIONS: A PICTORIAL REVIEW LESÕES BENIGNAS DA MANDÍBULA: UMA REVISÃO PICTÓRICA Francisco Rego Costa1, Cátia Esteves1, Maria Teresa Bacelar2 1Serviço de Radiologia do Hospital de São João, Abstract Resumo Porto 2Serviço de Radiologia do Instituto Português de Mandibular lesions are a common imaging fin- As lesões mandibulares constituem um Oncologia, Porto ding and they usually represent a diagnostic achado imagiológico frequente, representando Serviço de Radiologia do Instituto Português de challenge. This article intends to make a pictorial habitualmente um desafio diagnóstico. Este Oncologia do Porto. review of the most frequent benign mandibular artigo pretende realizar uma revisão pictórica Directora: Dra. Margarida Gouvêa lesions categorizing them according to their na- das lesões benignas mais comuns da mandíbula, ture (cystic or solid) and also according to their estratificando-as de acordo com a sua natureza origin (odontogenic/non-odontogenic and os- (quística ou sólida) e também de acordo com a seous/non-osseous). Odontogenic lesions will sua origem (odontogénica/não odontogénica Corresponding Author Address be designated accordingly to the World Health e óssea/não óssea). As lesões odontogénicas Organization (WHO) classification of odontoge- serão denominadas tendo por base a classificação Francisco Rego Costa nic tumors, published in 2005. da Organização Mundial de Saúde (OMS) dos Serviço de Radiologia The main objectives of this article are to describe tumores odontogénicos, publicada em 2005. Hospital de São João the epidemiologic, anatomic and imaging charac- Os principais objectivos deste artigo são descrever Alameda Prof. Hernâni Monteiro teristics of the most common benign mandibular as características epidemiológicas, anatómicas e 4200–319 Porto lesions, emphasizing the aspects that aid in the imagiológicas das lesões benignas mais comuns e-mail: [email protected] differential diagnosis; and to present some illus- da mandíbula, com ênfase nos aspectos que trative examples of these lesions in orthopanto- permitem realizar o diagnóstico diferencial; e mography, computorized tomography and mag- apresentar alguns exemplos ilustrativos destas Received 21/06/2016 netic resonance. lesões em ortopantomografia, tomografia Acceptance 24/07/2016 computorizada e ressonância magnética. Key-words Palavras-chave Mandibula; Benign lesions; Orthopantomography; Computorized Mandíbula; Lesões benignas; tomography; Magnetic resonance. Ortopantomografia; Tomografia Computorizada; Ressonância Magnética Introduction Benign Cystic Lesions Mandibular lesions are relatively common imaging findings. Cystic mandibular lesions are most often odontogenic. They can be encountered by head and neck-dedicated Their anatomic relationship with teeth is an important radiologists or by general radiologists. These lesions can be diagnostic clue. Usually they appear as lucent, well-defined, incidentally detected or actively searched for secondarily to uni or multilocular lesions. Cysts can predispose to infection patient’s symptoms or signs. They usually represent a diagnostic or pathologic fractures1,2. challenge. Knowledge of prevalence, imaging patterns and secondary signs that point to a specific diagnosis are essential Periapical (Radicular) Cyst for a thorough evaluation. Periapical cysts are the most common type of odontogenic Imaging can have a significant impact on treatment, cysts. They are slightly more common in men and have an supporting clinical decisions and avoiding unnecessary and incidence peak between 30 and 60 years. They result from invasive procedures. Panoramic radiograph (PR), computed infectious processes (abscess or granuloma) caused by tomography (CT) and magnetic resonance imaging (MRI) chronic apical periodontitis, usually associated with dental are most useful. The World Health Organization (WHO) cavities1-5. classification of odontogenic tumors, published in 2005, is still PR and CT (Fig. 1) show a lucent unilocular area around used worldwide and will be applied in this article. the root of a non-vital tooth, generally measuring less This article intends to accomplish a pictorial review of the than 1 cm in diameter. Dental root resorption or deviation most common benign mandibular lesions, emphasizing on and cortical expansion are possible complications. MRI anatomical, epidemiological and imaging aspects that are demonstrates lesions with high signal on T2-weighted crucial for narrowing the differential diagnosis. images (T2WI) and only peripheral enhancement. The term residual cyst should be used when referring to a lesion that persists after tooth extraction (Fig. 2)1-3. 25 Figure 3 – Dentigerous cyst. PR shows a lucent image around an unerupted mandibular 3rd molar (arrow). appear as well-circumscribed lytic lesions. They commonly affect men aged 50 years or older5,7. Odontogenic Keratocystic Tumor Odontogenic keratocystic tumors (OKT) are intraosseous benign lesions. Most are localized in the mandibular body or rami. These lesions can induce dental impaction but tooth involvement is not necessary (absent in one third of cases). They are more common in men and have an incidence peak Figure 1 – Periapical cyst. PR (A) shows a lucent rounded image around nd th the root of 4.1 (arrow). The tooth is fragmented. Bone window CT images between the 2 and 4 decades of life. in the coronal (B) and sagittal (C) planes demonstrate a hypodense lesion in Imaging appearance consists of uni or multilocular lesions the mandibular body, surrounding the 4.1 root (white arrows). The tooth is that can extend through “daughter cysts”. The walls of the fragmented and has a cavity (black arrow). lesion are thin but the contour may be lobulated owing to the coalescence of satellite lesions. Osseous expansion and cortical erosion can be evident, especially in large lesions. The internal content is cheese-like in consistency, which is responsible for the CT density as high as 50HU and for the variable signal on MRI T1WI and T2WI (Fig. 4 e 5)3-5,7,8. OKTs can have a locally aggressive behavior and the local recurrence rate after surgery is high (up to 60%). Squamous cell carcinoma malignant transformation is rare3-5,7,8. Basocelular Nevus (Gorlin-Goltz) syndrome should be suspected when multiple lesions are found in a young patient. Other hereditary syndromes such as Ehler-Danlos can be associated with multiple OKTs3-5,7,8. Figure 2 – Residual cyst. Bone window axial CT image shows a well-defined Simple Osseous Cyst hypodense image in the left mandibular body (arrow). Teeth are absent (extracted). Simple osseous cysts are pseudocysts that result from previous traumatic episodes, such as dental extractions, Dentigerous (Folicular) Cyst associated with bone bleeding. They are more common in Dentigerous cysts are the second most common type of women and tend to occur before 20 years. These lesions are odontogenic cyst (after periapical cysts) but are the most commonly located in the posterior mandibular medulla. They 1,4 common developmental (non-acquired) odontogenic cyst. are generally asymptomatic and found incidentally . These lesions form around the crown of an unerupted tooth Imaging studies demonstrate unilocular radiolucent lesions (usually the 3rd molar). They have an incidence peak at 20-40 of variable dimensions that do not induce erosion nor change years. teeth position. The internal content can be serous, associated PR (Fig. 3) and CT show well-defined unilocular lucent areas with high T2W signal or hemorrhagic, associated with variable around the crown of the 3rd molar (the root of the tooth is spontaneous CT density and MRI signal (that depends on the 1,4 not involved). The tooth follicular space should be greater age of blood). These lesions do not enhance . than 5 mm. Unlike periapical cysts, dentigerous cysts can grow to a large Static Bone Cavity (Stafne Cyst) size and induce teeth deviation and osseous remodeling, Stafne cysts are pseudocysts located in the lingual border although the cortex is usually preserved3,6. CT imaging is of the mandibular angle, caudally to the mandibular canal. important to determine cortical integrity and relationship They result from osseous remodeling due to the adjacent 1,3,4 with adjacent structures (mainly the mandibular canal), prior submandibular gland and are more common in men . to surgical intervention. MRI shows a lesion with signal They are well-defined radiolucent lesions, less than 2 cm in characteristics similar to periapical cysts and is used only in diameter, and represent cortical defects. Imaging evaluation 1,3,4 atypical cases1,3,4. is usually limited to panoramic radiograph . Periodontal Lateral Cyst These are less common odontogenic cysts. They form between the roots of teeth, usually in the premolar region and 26 Figure 4 – Odontogenic keratocystic tumor. Axial CT images after contrast administration in bone window (A) and soft tissue window (B) display a well-circumscribed lesion in the right mandibular body (arrows) with soft tissue density, associated with bulging and thinning of the outer cortex, without disruption. Figure 5 – Odontogenic keratocystic tumor. Bone window axial CT image (A) and PR (B) of the same patient. Image (A) shows a lesion in the transition between the body and the right mandibular ramus (arrow), with soft tissue density, that is responsible for bulging and thinning of the osseous cortex. Image (B) demonstrates