As a result of developments in ultrasound (US) technology and high-resolution ultrasonography (USG), US is now used in the examination and diagnosis of bone pathology of the paranasal sinuses and midface [1]. USG may be performed as a screening tool and to get a preliminary diagnosis even though a negative result does not certainly eliminate the possibility of pathology of the paranasal sinuses and midface. Because it is radiation-free, it may be recommended as a first step for the examination of pregnant women, young women, and children [2].

B-mode US images might be generated by mechanically moving an US probe on a trajectory, (i.e., a line), receiving RF-echo traces from each probe position, and then reconstructing the US image following numerous signal processing stages. A-mode USG is the most basic display mode right after plotting the RF-signal and it is progressively being substituted by B-mode USG in diagnostic imaging of the paranasal sinuses and midface [2, 3].

The frontal and maxillary sinuses are easier to visualize with USG owing to their superficial location. Sound waves penetrating through the anterior wall of the frontal and maxillary sinus are reflected by the air in the sinus, as the healthy sinuses are filled with air [4, 5]. However, in the presence of fluid or mucus inside the sinus cavity, sound waves can pass to the posterior wall of the sinus, thereby creating an ultrasound image of the sinus. The first layer is the skin and subcutaneous tissue in the US image of the healthy sinus. The second layer is the anterior wall of the maxillary sinus which is observed as well-defined, hyperechoic lines (Fig. 12.1) [5, 6]. The greater the volume of the mucosal thickening or fluid, the greater the visibility of the US wave [7].

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig1_HTML.jpg — Fig. 12.1

Normal maxillary sinus US image obtained with a 5–11 MHz linear probe. From outside to inside; mildly hypoechoic epidermis (orange arrow), subcutaneous adipose tissue (blue arrow) with hypoechoic lobule appearance, mildly hyperechoic soft tissue (yellow arrow), and hyperechoic maxillary anterior wall (green arrow) with smooth convex surface

Normal and pathological structures in the eyeball can be visualized with USG (Fig. 12.2). The eyeball is also fluid-filled which allows the imaging of tissues posterior to it such as orbit and ethmoid air cells [8]. However, the ultrasonic acoustic barrier prevents visualization of bony details and deep anatomic tissues, as is the case for posterior ethmoid air cells and sphenoid sinus [9].

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig2_HTML.png — Fig. 12.2

US image of a normal globe

Hockey stick and linear probes are preferred for imaging of the maxillofacial region [4–6]. When performing ultrasonographic examination in the paranasal sinuses, the upper body should be in an upright position with the head slightly tilted forward to obtain the appropriate image. Hyperextension or anteflexion of the head can differentiate effusion or fluid from other pathologies [4, 8].

The examination of the frontal and maxillary sinuses is always carried out in longitudinal and transverse planes. It is important to compare the patient’s right and left side findings. To evaluate the maxillary sinus, the probe is placed at the level of the infraorbital nerve on the anterior wall of the maxillary sinus (Figs. 12.3 and 12.4). The region is examined by moving the probe in the craniocaudal and mediolateral directions. Positioning the probe at different angles allows a full examination of the area of interest. During the ultrasonographic evaluation of the frontal sinus, the probe must be positioned between and just above the eyebrows (Figs. 12.5 and 12.6). High gain, a penetration depth of ±60 mm, and as low insonation frequency as possible should be adjusted in advance [8].

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig3_HTML.png — Fig. 12.3

Photograph showing patient and ultrasound probe positioning for maxillary sinus examination

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig4_HTML.png — Fig. 12.4

US image of normal maxillary sinus. ASW: Anterior sinus wall

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig5_HTML.png — Fig. 12.5

Photograph showing patient and ultrasound probe positioning for frontal sinus examination

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig6_HTML.png — Fig. 12.6

US image of normal frontal sinus of frontal bone

12.2 Diseases of Paranasal Sinuses and Midface: A Brief Review of Typical USG Aspect of the Most Frequently Encountered Pathologies

12.2.1 Inflammatory Changes

12.2.1.1 Sinusitis

US has a significant value in the evaluation of sinusitis of maxillary sinuses, especially acute sinusitis as maxillary sinuses are generally affected. The normal sinus can be accurately diagnosed as healthy because of the total reflection of the air-filled normal sinus [2].

When the sinus is filled with fluid material such as secretion, pus or mucus, sound waves passing through these inflammatory products are reflected by the posterior wall of the sinus cavity giving a visible “posterior wall echo.” The posterior wall echo, which is observed in the echogram, indicates that there is a pathological condition in the sinus. When there is fluid collection (i.e., sinusitis) in the paranasal sinus, anechoic to hypoechoic with scarce isolated internal echoes, homogeneous or heterogeneous, well-defined, triangle shape (maxillary sinus) is observed in the image, whereas in case of mucosal thickening, hypoechoic to echoic, non-triangular shape image with unclear boundaries is observed [4–6, 8].

The USG examination is done while the patient is sitting in an upright position, with the head at an angle of 90 degrees flexion to concentrate any fluid characteristics of the sinusitis on the anterior sinus wall (Figs. 12.7 and 12.8) [4, 10]. Swelling of adjacent soft tissues, following interruption of bony structures in presence of aggravated inflammatory process, can be seen [8].

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig7_HTML.jpg — Fig. 12.7

Photograph showing patient and ultrasound probe positioning for frontal sinus examination in presence of fluid collection (i.e., sinusitis). The patient is in a seated position and the neck is anteriorly flexed to concentrate any fluid characteristics of the sinusitis on the anterior sinus wall. The 5–11 MHz linear probe is placed in the medial part of the orbit and angled to the proximal part of the nasal region

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig8_HTML.jpg — Fig. 12.8

Photograph showing patient and ultrasound probe positioning for maxillary sinus examination in presence of fluid collection (i.e., sinusitis). The patient is in a seated position and the neck is anteriorly flexed to concentrate any fluid characteristics of the sinusitis on the anterior sinus wall. Maxillary sinus is visualized from the anterior wall with a 5–11 MHz linear probe

12.3 Benign Lesions

12.3.1 Paranasal Sinuses

Generally, benign tumors display homogeneous internal echoes, round or oval shape, and clear margins [9]. The visualization of the tumor is not dependent on the head position. If the USG performed while moving the patient’s head at different angles shows that the sinus content does not change in thickness; this implies the existence of a solid hypoechoic lesion [4, 10]. In the presence of a lesion in the paranasal sinuses and nasal cavity, the surrounding bone and air improve the contrast of the hypoechoic mass significantly, that facilitates defining the margins of the masses [9].

When a mass is in contact with the anterior wall of the paranasal sinus, US waves continuously propagate to extend to the posterior wall of the sinus. In this case comparison with the contralateral side may exclude the probability of pansinusitis [4, 10]. Since mucous retention pseudocysts often originate from the floor of the maxillary sinus, they will not be detected by USG unless the pathology contacts with the anterior wall of the maxillary sinus [11]. Mucus retention phenomenon and the more aggressive but less common mucoceles that are in contact with the anterior wall might be visualized as space-occupying round lesions. Structures located posterior to the air-filled regions are not observable and an isolated pathology on the posterior wall of the air-filled sinus will not be detected [8].

Benign lesions of the paranasal sinuses like adenoma or mycetoma can be seen on USG in some particular cases and may be difficult to differentiate from inflammatory process. Several heterogeneous reflecting structures neighboring the anterior wall and probably reaching the posterior wall of the sinus might be detected. The intense, irregular echo form differentiates these lesions from mucus retention pseudocyst, mucocele, or effusion that has distinct US features extending from anterior to the posterior wall. The multiple reflections are a strong indication of a solid lesion in the paranasal sinuses [8].

12.3.2 Midface

12.3.2.1 Pilomatrixoma

Pilomatrixoma, also called pilomatricoma, is a benign skin neoplasm thought to originate from hair follicle matrix cells. It occurs as a purplish or single skin-colored lesion on the head and neck region. It is characterized by calcification inside the lesion resulting in hard and bony feeling and frequently appears as angulated shape (tent sign) [12]. USG typically demonstrates target-like lesions with a hypoechoic rim, hyperechoic center, and, frequently, with internal hyperechoic dots consistent with calcium deposits (Figs. 12.9a, b and 12.10a, b) [13].

../images/484215_1_En_12_Chapter/484215_1_En_12_Fig9_HTML.png

Tags: Ultrasonography in Dentomaxillofacial Diagnostics

Aug 7, 2022 | Posted by mrzezo in Oral and Maxillofacial Radiology | Comments Off

Pocket Dentistry

Fastest Clinical Dentistry Insight Engine

Anatomy and Pathology: Paranasal Sinuses and Midface

12. Sonographic Anatomy and Pathology: Paranasal Sinuses and Midface

12.1 Anatomy