20 Sinuses



10.1055/b-0036-138093

20 Sinuses



20.1 Nasal Cavity and Paranasal Sinuses


The paranasal sinuses are aerated cavities within the facial bones that serve a variety of roles, including the humidification of inhaled air, contributing to immunologic defenses, and decreasing the weight of the skull. A variety of infectious, inflammatory, and neoplastic entities can occur within the paranasal sinuses throughout childhood and adolescence, largely mirroring pathologic conditions in adults. Additionally, there are a variety congenital abnormalities of the paranasal sinuses, and variants of these abnormalities, that require awareness.



20.2 Anatomy


There are four pairs of paranasal sinuses, within different facial bones (Fig. 20.1). The largest are the maxillary sinuses, which are lateral to the nasal cavity, below the orbits and above the posterior maxillary alveolus. The maxillary sinuses communicate with the nasal cavity through the osteomeatal complex, and drain near the hiatus semilunaris. The ethmoid sinuses are a multiseptated series of air cells located above the nasal cavity and medial to the orbit. The ethmoid sinuses are separated from the orbit by the lamina papyracea. Superiorly, the ethmoid sinuses are separated from the anterior cranial fossa by the cribriform plate medially and the fovea ethmoidalis laterally. The frontal sinuses, in the frontal bones superior to the anterior aspect of the orbits, drain through a frontoethmoidal recess that extends toward the hiatus semilunaris. Posterior to the ethmoid bones are the sphenoid sinuses, which develop within the basisphenoid. The sphenoid sinuses drain into the posterior ethmoid sinuses through the sphenoethmoidal recess (s. Tab.).

Fig. 20.1 Anatomy of paranasal sinuses. (a) Diagram of a coronal section through the frontal, ethmoid, and maxillary sinuses showing the osseous boundaries of the sinuses and their relationship to the nasal cavity and orbits. (b) Diagram of a sagittal section through the nasal cavity, showing drainage pathways of the paranasal sinuses as they relate to the hiatus semilunaris and nasal turbinates. From Atlas of Anatomy, © Thieme 2012, Illustration by Karl Wesker.















































Table 20.1 Nasal passages into which the paranasal sinuses empty

Sinuses/Duct



Nasal passage


Pathway


Sphenoid sinus



Sphenoethmoidal recess


Direct


Ethmoid sinus


Posterior cells


Superior meatus


Direct



Anterior and middle cells


Middle meatus


Ethmoid bulla


Frontal sinus



Middle meatus


Frontonasal duct into hiatus semilunaris


Maxillary sinus



Middle meatus


Hiatus semilunaris


Nasolacrimal duct



Inferior meatus


Direct


Used with permission from Gilroy A, MacPherson B, Ross L. Head & Neck: Nasal Cavity and Nose. In: Gilroy A, MacPherson B, Ross L, eds. Atlas of Anatomy. 2nd ed. New York, NY: Thieme;2012:552.



The sinuses develop over the course of childhood. The ethmoid sinuses are present at birth, as are the maxillary sinuses in their rudimentary form. The maxillary sinuses develop over the first decade of life, followed by the sphenoid sinuses and, variably, the frontal sinuses (Fig. 20.2). The sphenoid sinuses develop within the basisphenoid, and at times there is lateral pneumatization of pterygoid recesses extending into the pterygoid process of the sphenoid bone. In some children, the development of the sphenoid sinus is arrested, typically in an asymmetric manner (Fig. 20.3). It is important to be aware of this entity because it can be mistaken for a lesion of the skull base.

Fig. 20.2 Sinus development. Diagram showing the pattern of sinus development for the frontal and maxillary sinuses. Note that there is a great degree of variability on an individual basis. From Atlas of Anatomy, © Thieme 2012, Illustration by Karl Wesker.
Fig. 20.3 Arrested pneumatization. Axial computed tomographic image of the head of a 12-year-old girl shows a somewhat lytic lesion in the sphenoid bone (red arrow), with a thin, circumscribed, sclerotic margin and heterogeneous internal matrix, in the expected location of a developing sphenoid sinus. These findings are consistent with arrested pneumatization of the sphenoid sinus, which is a variant of normal development.



20.3 Sinonasal Infections


Sinonasal infections are common throughout childhood. Mucosal thickening along the margins of the paranasal sinuses does not necessarily represent an acute bacterial sinusitis. Focal globular thickening usually represents a mucous retention cyst (Fig. 20.4) rather than a polyp. Discrete polyps are typically not visible on cross-sectional imaging. The presence of fluid levels or bubbly secretions may be indicative of acute sinusitis, but fluid levels alone are nonspecific, and can be seen after swimming. The drainage pathways to a sinus can become obstructed, preventing the drainage of infectious debris and possibly exacerbating symptoms of sinusitis (Fig. 20.5). Acute sinusitis can result in bony erosion.

Fig. 20.4 Mucous retention cyst. (a) Coronal bone algorithm computed tomographic image shows a homogeneous, circumscribed, soft tissue lesion in the inferior aspect of the left maxillary sinus (red arrow). (g) Coronal short tau inversion recovery image shows the lesion to be diffusely hyperintense. This represents a mucous retention cyst.
Fig. 20.5 Sinus anatomy and drainage pathways. (a) Coronal computed tomographic image of the sinuses in a 6-year-old girl shows the maxillary sinus (red arrow), which drains through the osteomeatal complex (red arrowhead) to the middle meatus, adjacent to the drainage of a middle ethmoid air cell (green arrow). (b) Axial image shows the sphenoid sinus (green arrow) draining through the sphenoethmoidal recess (green arrowhead). (c) Sagittal computed tomographic image shows drainage of the frontal recess (green arrowheads), also to the middle meatus; however, the frontal sinuses themselves have not yet developed in this patient.


Three complications of acute sinusitis require awareness. The first is erosion through the lamina papyracea, which can result in orbital cellulitis (Fig. 20.6). The other two, Pott’s puffy tumor, and epidural/subdural empyema, originate from the frontal sinuses, and can extend through the anterior wall into the subcutaneous soft tissues of the forehead, resulting in the swelling known as Pott’s puffy tumor (Fig. 10.2) (which despite its name is a non-neoplastic condition). The extension of an infectious process in the frontal sinus through the posterior wall can result in its further intracranial extension and an epidural and/or subdural empyema (Fig. 10.2), which is a surgical emergency.

Fig. 20.6 Orbital abscess/cellulitis. (a) Coronal contrast-enhanced computed tomographic image of the head of a 21-month-old girl shows mucosal disease of the right maxillary sinus (blue arrow) and a fluid collection in the medial extraconal space of the right orbit (blue arrowhead). (b) Axial computed tomographic image shows the fluid collection (blue arrowhead), which is probably a subperiosteal abscess along the orbital margin of the lamina papyracea, and lateral deviation of the right medial rectus muscle (red arrowheads).


Chronic infection can result in thickening and sclerosis of the osseous margins of the paranasal sinuses (Fig. 20.7).

Fig. 20.7 Chronic sinusitis. Axial bone algorithm computed tomographic image of the head of a 10-year-old boy shows nearly complete opacification of the right maxillary sinus. There is thickening of the bony margins of the posterior wall of the maxillary sinus (red arrowheads), representing the osteitis of chronic sinusitis.


A subtype of chronic sinusitis is allergic fungal sinusitis (Fig. 20.8). The characteristic appearance of this on imaging is that of high-density matter within the paranasal sinuses. The high density represents noninvasive fungal hyphae, with the density possibly also related to the presence of metalloproteases. The chronic space-filling process in this sinusitis can result in expansion of the sinuses and even in hypertelorism (Fig. 20.8). When suggesting this diagnosis, it is important to specifically state that the diagnosis is allergic fungal sinusitis, which is a chronic process. This is in contradistinction to invasive fungal sinusitis, an acute aggressive process seen most commonly in immunocompromised patients and which represents a surgical emergency.

Fig. 20.8 Allergic fungal sinusitis with hypertelorism. (a) Sagittal computed tomographic image of the head of a 14-year-old boy with headaches shows high-density contents in the right frontal, ethmoid, and sphenoid sinuses. (b) Axial soft tissue algorithm computed tomographic image shows that the sinuses are filled and somewhat expanded in this patient with polyposis and allergic fungal sinusitis.


A partial obstruction of the osteomeatal complex of the maxillary sinuses can effectively create a one-way valve. If this allows air to move out of the sinus more easily than it can move into the sinus, it will result in a chronic vacuum effect within the sinus, causing the sinus to become smaller over the course of time. An asymmetrically smaller, or atelectatic, maxillary sinus is a sequela of this chronic sinus problem that may be clinically asymptomatic, yielding the name “silent sinus syndrome” (Fig. 20.9). This is important to recognize because the syndrome can eventually result in lowering of the floor of the orbit, creating visual symptoms, such as double vision.

Fig. 20.9 Silent sinus syndrome. Coronal computed tomographic image of the head of a 13-year-old girl with headache but no history of sinusitis shows an asymmetrically smaller right than left maxillary sinus, with patent osteomeatal complexes bilaterally. Maxillary hypoplasia can be related to silent sinus syndrome.

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May 28, 2020 | Posted by in NEUROLOGICAL IMAGING | Comments Off on 20 Sinuses
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