Para los pacientes que han abandonado recientemente Tratamientos para los exfumadores recientes

The osseous components of the temporomandibular joint (TMJ) include the mandibular condyle, glenoid (mandibu-lar) fossa, and, anteriorly, the articular tubercle (the bony eminence of the temporal bone). The TMJ disk is a bicon-cave structure, with a thick periphery and a thin center.

In the sagittal plane the disk appears biconcave, in the coronal plane crescent-shaped. The anterior and poste-rior parts of the disk are referred to as the anteposte-rior and posterior bands. In the normal closed position, the poste-rior band is located at 12:00 over the condyle. In a normal joint, regardless of position (open or closed), the central thin portion of the disk remains interposed between the condyle and the articular tubercle.

The most common internal derangement of the TMJ is disk displacement, which is usually anterior or anterome-dial. Displacement (dislocation) can occur with or with-out reduction (the disk reverting to its normal position) on opening ( Fig. 2.84 ). A “click” heard on opening can occur due to reduction of an anterior disk displacement. In a disk displacement without reduction, the disk remains displaced anteriorly regardless of jaw position. Jaw open-ing may be limited, in this instance, on the aff ected side.

Disk deformity occurs late in the disease stage, with asso-ciated degenerative bony changes including fl attening of the condyle and small osteophytes. The upper and lower compartments (joint spaces, above and below the disk) normally do not communicate. TMJ arthrography is rou-tinely performed in specialty centers, either of the lower joint space alone or of both joint spaces. CT of the TMJ is the best means of examining the osseous joint structures.

Fig. 2.81 Ameloblastoma. This 43-year-old patient pre-sented with swelling and discomfort involving the man-dible for more than 20 years. Two axial CT images are presented, depicting a large, expansile, destructive lytic mandibular lesion. The mass is at least, in part, multilocu-lated, a feature best seen on the more caudal of the two images. Although matrix calcifi cation is not typical of an ameloblastoma, fragmented bone can be present, as in this case, due to the destructive nature of the lesion.

On MR today, at 3T using bilateral dedicated multichannel surface coil arrays, true dynamic imaging of the TMJ can be accomplished, with a temporal resolution of one-fourth of a second. This should be supplemented by high resolution static images in both the open and closed position in the sagittal and coronal planes. Regardless of pulse sequence, the disk will have low signal intensity. T2-weighted im-ages can also be acquired to identify abnormal joint fl uid or edema in the adjacent tissues.

■ Nasopharynx

The roof of the nasopharynx is formed by the sphenoid sinus and upper clivus. The posterior margin is formed by the lower clivus and upper cervical spine. Anteriorly lies the nasal cavity. The lateral walls are formed by the ptery-goid plates (anteriorly) and the fascia and muscles of the airway (posteriorly). The nasopharynx is separated from the oropharynx below by the soft palate. The levator and tensor veli palatini muscles arise from the skull base, at-tach to the soft palate, and function to elevate and tense the palate. The pharyngobasilar fascia holds the airway patent. It surrounds the mucosa, superior constrictor, and Fig. 2.82 Mandibular fracture with condylar displacement. Axial images (part 1) display a subcondylar fracture on the right, and a parasymphyseal fracture on the left. Coronal reformatted images (part 2) display well both fractures, with the subcondylar fracture grossly angulated (arrow) and, in addition, dislocation or subluxation of the left mandibular condyle (*). Close inspection of the condyles, evaluating for displacement/subluxation, is advised in all facial trauma.

Fig. 2.83 Mandibular fracture. Because it is, in essence, a ring (when considered with the skull base), fractures of the mandible are often—but not always—multiple. Coronal reformatted images display two fractures, one at the angle of the mandible on the right (black arrow) and one through the body on the left (white arrows), parasymphyseal in location. For a single fracture that involves the mandible, the angle of the mandible is the most common location.

The fracture on the right did traverse the inferior alveolar canal (images not shown), with thus the potential for damage to the in-ferior alveolar nerve.

levator veli palatini muscles, and separates the nasopha-ryngeal mucosal space from surrounding fascial spaces.

The nasopharyngeal mucosal space contains mucosa, adenoidal tissue, the superior constrictor muscle, the torus tubarius, levator veli palatini muscles, and many minor salivary glands. The mucosa and normal adenoi-dal tissue are high signal intensity on T2-weighted MR images. The eustachian tubes end in the torus tubarius (a lateral cartilaginous enlargement). The lateral pharyn-geal recess (fossa of Rosenmüller) is formed by mucosal refl ection over the longus colli and capitis muscles (fl exors of the cervical spine), and is the site of origin for the vast majority of nasopharyngeal carcinomas (NPC). The leva-tor veli palatini muscle is intrapharyngeal, just lateral to the torus tubarius. The tensor veli palatini muscle is lateral

to the pharyngobasilar fascia and surrounded by fat. The retropharyngeal space is a potential space between the pharyngeal constrictor muscles anteriorly and the pre-vertebral muscles posteriorly. The prepre-vertebral (periver-tebral) space is bounded by the prevertebral fascia ante-riorly and the vertebral bodies posteante-riorly, contains the prevertebral muscles, and extends from the skull base to the coccyx.

Infection involving the nasopharynx is usually second-ary to either dental or tonsillar infection. Dental infection can spread to the masticator and prestyloid parapharyn-geal spaces, in addition to causing osteomyelitis. Tonsil-lar infection can result in an abscess that can extend to the retropharyngeal space or the prestyloid parapharyn-geal space.

Fig. 2.84 Temporomandibular joint, disk displacement. The normal appearance of the TMJ is demonstrated in closed and open mouth views (fi rst row). The mandibular condyle is located anterior to the external auditory meatus with its head articulating with the glenoid fossa and articular eminence of the temporal bone. When the mouth is closed (fi rst column), the mandibular condyle lies centered in the glenoid fossa with the meniscus (black arrow) lying along its antero-superior aspect. With mouth opening, the condyle (C) translocates anteriorly with the meniscus moving into the one o’clock position.

The most common cause of TMJ dysfunction is an anterior reducible dislocation of the meniscus (second row). In the closed mouth view,

the low SI meniscus (white *) is located anterior to the mandibular condyle with the condyle resting on retrodiskal tissue. In the open mouth view, second column, the condyle translocates anteriorly underneath the posterior band of the meniscus, with the meniscus (white arrow) now assuming a normal position (reduction of the dis-location). In a fi xed-type of dislocation (third row), the meniscus is seen anterior to the mandibular condyle in the closed-mouth view, and remains dislocated (black *) anteriorly to the condyle in the open mouth view. Often a fi xed, chronically dislocated meniscus will appear deformed or compressed due to repetitive trauma during opening and closing of the mouth.

Benign, incidental soft tissue masses in the nasopharynx include adenoidal hypertrophy (seen in children and young adults), and the Tornwaldt cyst. The latter is very common, seen in 4% of patients, and is a small midline cyst that lies along the posterior nasopharyngeal wall. A Tornwaldt cyst will have high signal intensity on T2, refl ecting fl uid, and intermediate to high signal intensity on T1-weighted im-ages, dependent on the protein concentration.

Nasopharyngeal carcinoma is by far the most common malignant tumor of the nasopharynx, strongly associated with Epstein-Barr virus infection. The lateral pharyngeal re-cess is the most common site of origin. These tumors often cause eustachian tube obstruction, due to involvement of

the levator veli palatine muscle, resulting in a middle ear eff usion ( Fig. 2.8 ). A tumor in this location can grow in any direction, with lateral extension most common. Eighty to 90% of patients have nodal involvement on presentation (retropharyngeal, level II and level V) ( Fig. 2.85 ). Involve-ment of lymph nodes can be suggested on many diff erent bases—by size criteria, with visualization of necrosis, and by restricted diff usion, with FDG PET extremely valuable for identifi cation of tumor involvement (above a certain size). It is important to note that radiation therapy causes a substantial change in appearance of tissues in this region on both CT and MR, with fi brosis having low signal inten-sity on both T1- and T2-weighted images.

Fig. 2.85 Nasopharyngeal carcinoma, undiff erentiated, with exten-sive cervical nodal metastases. Abnormal enhancing soft tissue is present on the right in the posterior nasopharynx at the level of the ostium of the eustachian tube, centered on (and obliterating) the fossa of Rosenmüller (pharyngeal recess), as well as extend-ing slightly across the midline (part 1, arrow). Tumor margins are relatively well delineated on MR, as compared to CT, with the latter

modality demonstrating only soft tissue prominence. Coronal imag-ing, both MR and CT (part 2), reveals extensive bilateral lymphade-nopathy, consistent with metastatic spread. Also note the middle ear and mastoid fl uid due to eustachian tube obstruction. Positron emission tomography (PET) CT (part 3) identifi es the primary lesion in the right nasopharynx with slight extension across the midline, together with involved level II lymph nodes bilaterally.

(HPV). Other much less common malignant lesions include non-Hodgkin lymphoma and minor salivary gland tumors.

Half of all minor salivary gland tumors in this region are malignant. In regard to the tongue, squamous cell carci-noma easily spreads along the intrinsic muscles. In image interpretation, it is important to assess spread in relation to the midline. Without midline extension, hemiglossec-tomy is a surgical option ( Fig. 2.88 ). The most common oral cavity tumor is squamous carcinoma of the lower lip. Other common sites include the tongue, fl oor of the mouth, retromolar trigone, and hard palate.

Within the oropharynx, tonsil carcinoma is the most common squamous cell carcinoma, with a strong HPV association ( Fig. 2.89 ). In this location in particular, there is a very high incidence of nodal metastases at Rhabdomyosarcoma is the most common sarcoma in

pediatrics and young adults. Forty percent of these lesions occur in the head and neck, with the most common loca-tions being the orbit and nasopharynx. This tumor is lo-cally invasive, often with bone destruction and perineural tumor extension.