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K. Orhan (ed.)Ultrasonography in Dentomaxillofacial Diagnosticsdoi.org/10.1007/978-3-030-62179-7_12
12. Sonographic Anatomy and Pathology: Paranasal Sinuses and Midface
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 . 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 .
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].
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].
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
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 .
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].
12.3 Benign Lesions
12.3.1 Paranasal Sinuses
Generally, benign tumors display homogeneous internal echoes, round or oval shape, and clear margins . 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 .
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 . 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 .
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 .