10.1 General Consideration for Application of Ultrasound in TMJ Diagnostics

In diagnostics of TMJ high-frequency linear probes (preferably over 12 MHz) with a relatively small “footprint” are used as they offer high resolution of image with a relatively low penetration depth which is sufficient in examinations of these superficially located joints. Intraoral probes are useful in imaging of masticatory muscles, instead of infrequent finger probes or finger-tip probes, an intraoperative “hockey stick” probe can be successfully applied.

US scanning of TMJ is performed in a patient lying on a special examination bed or sitting upright. A water-soluble gel is generously administered on the patient’s skin within the region of interest in order to eliminate air bubbles from between the skin and the probe since ultrasound is strongly reflected by gases [1, 2]. The transducer is then placed parallel to the Frankfurt horizontal plane and at 60–100° to the plane, parallel to the ramus of mandible, both in open and closed mouth position (Fig. 10.1a–d). However, it must be remembered that since US is a dynamic real-time examination, during the study the probe has to be moved gently over the studied area. Therefore the US images are never truly transverse or sagittal [3]. This obstacle can be overcome by using a 3D US probe [4, 5]. During the examination, multiple images are captured and the condyle movement range can be registered as well. Complementary US scanning of masticatory muscles may be performed.

One of the disadvantages of US is high dependency on operator’s skills and experience [6]. Another disadvantage of the utmost importance in diagnostics of TMJ is that it is not possible to demonstrate structures located behind the intact bone surface, as the beam is fully reflected off dense outer cortex. Therefore, only a part of TMJ is accessible for US—the articular capsule, the disc, and cortex of laterosuperior aspect of the condyle are visible [7]. Another limitation of TMJ US imaging is osteoarthritis with reduction of joint space width and formation of bony spurs further decreasing area available for penetration with an ultrasound beam [1]. All this discourages some operators from using US in this joint at all, and MR is preferred for that purpose [8].

Reported sensitivity, specificity, and accuracy values of ultrasound vary in broad ranges, e.g., according to Melis et al. [9] sensitivity of US in assessment of disc displacement falls between 13 and 100%, specificity from 62 to 100% and accuracy in the range of 51.8 to 100%. In a meta-analysis by Dong et al. [10] comprising 1096 subjects from 11 studies, for anterior disc displacement with reduction, the pooled sensitivity and specificity were 83% and 85%, respectively while for the anterior disc displacement without reduction the weighted sensitivity and specificity values were 102% and 90%, respectively.

10.2 Indications and Contraindications for TMJ Ultrasound

As far as TMJ is concerned, the following applications were described:

• Joint effusion [11, 12].

• Internal derangement [13] and disc displacement, mainly anterior with and without reduction [5, 7, 14–18]; no studies reported data on lateral or posterior disc displacement [19].

• Osteoarthrosis including condylar erosion [4, 6, 20, 21].

• Rheumatoid, psoriatic, and juvenile idiopathic arthritis with TMJ involvement as well as polyarthritis [12, 22–26].

• Joint function basing on condylar translation range [27–32].

• Condylar movement using Duplex Doppler [33].

• Intraarticular TMJ dislocation [34].

• Guidance in fine needle aspiration cytology (FNAC).

• Guidance for TMJ arthrocentesis [35].

• Guidance in TMJ injections, e.g., with steroids.

• Soft tissue masses around TMJ (Fig. 10.2).

There are neither contraindications for ultrasound scanning nor special patient preparation required. Use of a gel stand-off pad may be necessary in case of very superficially located lesions, but a thick layer of gel with limited pressure on the probe may be applied in its stead (Ahuja and Evans 2013).

10.3 Normal Anatomy of TMJ in Ultrasound

Normal anatomy of TMJ in ultrasound is presented in Figs. 10.3, 10.4, 10.5, 10.6, 10.7 and 10.8.

10.4 Ultrasonography-Guided Invasive Procedures

10.4.1 Fine-Needle Aspiration Biopsy

The golden standard for diagnosis of pathologies concerning the temporomandibular joint is histopathological evaluation. In literature, fine needle aspiration biopsy is a proven method for obtaining pathological specimen and continuing histopathological evaluation.

Ultrasonography guidance while reaching the pathology is one of the primary methods that will ensure results that are more accurate. Features like easy access to this technology, ease of use for the radiologist, being a noninvasive procedure, and easily tolerated by the patients have made this technology a routine while performing fine needle aspiration biopsy.

Ultrasonography guided fine needle aspiration biopsy is a minor invasive procedure which can take place in an ambulatory setting, the patient can be discharged the same day and go back to the daily routine.

10.4.2 Ultrasonography-Guided Fine Needle Aspiration Biopsy

Being an invasive procedure fine needle aspiration biopsy should be planned under sterile conditions. Preparations should be made and checked before biopsy. As a minimal invasive method, ultrasonography-guided fine needle aspiration biopsy could be realized with only one operator, while two operators are commonly preferred. One operator to perform the ultrasonography and guide the procedure while the other performs biopsy.

Before passing on to the procedure the anatomy of the region and pathology should be thoroughly examined with ultrasound by both the operators. This will give both the operators advantage before performing the biopsy. The area should then be wiped from the ultrasonography gel.

Sterile gloves should be worn and the region should be cleaned with skin disinfectants to achieve antisepsis. A local anesthetic solution containing 1:100.000 epinephrine should be carefully and slowly injected inside the temporomandibular joint capsule using a 210-gauge needle. This careful and slow application of local anesthetic should prevent any discomfort during the procedure.

After local anesthetic injection, the region must be palpated and “manually sensed.” During palpation of the region, the patient should be instructed to slowly open and close the jaws. This motion will be helpful for detecting the zygomatic arch and mandibular condyle.

To identify the entrance point of the needle a soft ruler and dermal pen can be used. The ruler should be directed from the outer cantus of the eye to the tip of the outer ear tragus. On this imaginary line, a mark should be made 10 mm away anteriorly from the tragus tip. Another mark should be made on a second imaginary line parallel to the first one just 2 mm below the first mark. This second mark will be the entrance point of the needle. There will be approximately 25 mm from the skin mark to the temporomandibular joint.

A 23- or 210-gauge needle should be preferred. To increase the joint space patient should be instructed to open the jaws widely. The radiologist should then position the ultrasonography probe anterior to the entrance point. This settlement will ensure a comfortable procedure for the operator performing the biopsy. After visualization of the temporomandibular joint structures and associative pathology, the needle should be inserted from the specified mark with the bevel facing the temporomandibular joint. After some advancement, the tip of the needle should be recognized through ultrasonography. The needle should be then advanced into the structures in a posterior and superior route, into the pathology (Fig. 10.9).

Coordination between the two operators is essential during this phase. The ultrasonography operator should help the other operator channel the needle in the correct direction. After access to the pathology, the needle should be advanced to the center of the lesion. Under mild vacuum applied with the plunger, biopsy specimen should be obtained with light forward-backward movements of the needle. The needle should then be removed while mild vacuum continues and the specimen should be spread on a lamella. The specimen should then be sent for histopathological evaluation.

Following biopsy, the area should be closed with a sticking plaster with slight pressure, to prevent hematoma formation. Intermittent cold-pack applications and anti-inflammatory medication will be useful during the postoperative period.

10.4.3 Core Biopsy

Core biopsy is an invasive method, in need of special equipment. While soft tissue core biopsy needles measure around 1 mm, hard tissue core biopsy needles may measure up to 2 mm diameter. The core biopsy needle, produced especially for this procedure, enters the lesion while its blade is closed; when it is triggered the blade opens and closes at high-speed, obtaining the specimen. The specimen with an approximate length of 1 cm is then extracted. This large tissue is very valuable for a correct histopathological diagnosis. Thus, the most important advantage of core biopsy is that chance of accurate histopathological diagnosis is higher and additional biopsy procedures are needed less. Nevertheless, hemorrhage may occur more frequently during this procedure.

10.4.4 Ultrasonography-Guided Core Biopsy

Preoperative preparation and technique are similar to those of fine needle aspiration biopsy. However, postoperative complications such as pain and edema will be more excessive since wider needles are used, the entrance port is larger and larger amount of tissue is incised.

Core biopsy under ultrasonography guidance will reduce the reliability of the procedure, lower the need for additional biopsies, and shorten operation time while reducing patient comfort.

10.4.5 Intraarticular Sodium Hyaluronate Injection

Sodium hyaluronate is a material similar to the synovial fluid produced in the temporomandibular joint. It serves as a lubricant and absorber of traumas. It is commonly used to treat temporomandibular joint osteoarthritis. It is an agent effective in decreasing temporomandibular joint pain associated with intraarticular derangements unresponsive to conservative treatments.

10.4.6 Ultrasonography-Guided Sodium Hyaluronate Injection

Preoperative preparation and technique are similar to those of fine needle aspiration biopsy. The procedure should be planned under sterile conditions. Preparations should be made and checked before biopsy. As a minimal invasive method, ultrasonography-guided sodium hyaluronate injection could be performed by one operator only, while two operators are commonly preferred.

Before passing on to the procedure, the anatomy of the region and pathology should be thoroughly examined with ultrasound by both the operators. This will give both the operators advantage before performing the procedure. The area should then be wiped from the ultrasonography gel.

Sterile gloves should be worn and the region should be cleaned with skin disinfectants to achieve antisepsis. A local anesthetic solution containing 1:100.000 epinephrine should be carefully and slowly injected inside the temporomandibular joint capsule using a 210-gauge needle. This careful and slow application of local anesthetic should prevent any discomfort during the procedure.

After local anesthetic injection, the region must be palpated and “manually sensed.” During palpation of the region, the patient should be instructed to slowly open and close the jaws. This motion will be helpful for detecting the zygomatic arch and mandibular condyle.

To identify the entrance point of the needle a soft ruler and dermal pen can be used. The ruler should be directed from the outer cantus of the eye to the tip of the outer ear tragus. On this imaginary line, a mark should be made 10 mm away anteriorly from the tragus tip. Another mark should be made on a second imaginary line parallel to the first one just 2 mm below the first mark. This second mark will be the entrance point of the needle. There will be approximately 25 mm from the skin mark to the temporomandibular joint.

To increase the joint space patient should be instructed to open the jaws widely. The radiologist should then position the ultrasonography probe anterior to the entrance point. This settlement will ensure a comfortable procedure for the operator performing the biopsy. After visualization of the temporomandibular joint structures and associative pathology, the needle should be inserted from the specified mark with the bevel facing the temporomandibular joint. After some advancement, the tip of the needle should be recognized through ultrasonography. The needle should be then advanced into the structures in a posterior and superior route, into the pathology. Sodium hyaluronate preparations are usually present in ready-to-use syringes. If such syringes are used the presented needles should be used. If no needle is present, a 19-gauge needle can be used (Fig. 10.10).

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