Corpus: Paranasal sinus

The paranasal sinuses are air-filled, paired outpouchings of the nasal cavity that are lined with respiratory epithelium. They are located between the two bone plates (tabula externa and interna) of some skull bones and thus pneumatise them. Anatomically, the paranasal sinuses are assigned to the inner nose and thus to the respiratory system.

The following paranasal sinuses are found in humans:

• Sinus frontalis (frontal sinus)
• maxillary sinus (maxillary sinus)
• Cellulae ethmoidales (ethmoidal cells)
• Sphenoid sinus (sphenoidal sinus)

Depending on the drainage route, a distinction is made between the anterior and posterior compartments:

Anterior compartment[Bearbeiten]

The anterior compartment consists of the frontal sinus, maxillary sinus and the anterior ethmoidal cells. The maxillary sinus and the anterior ethmoidal cells drain into the ethmoidal infundibulum, which is bounded medially by the uncinate process. The infundibulum opens into the nasal cavity via the semilunar hiatus. The frontal sinus opens directly into the middle nasal passage via its excretory duct or indirectly via the ethmoidal infundibulum. The entirety of the excretory ducts of the anterior compartment and their bony boundaries are referred to as the ostiomeatal complex.

Posterior compartment[Bearbeiten]

The posterior compartment consists of the sphenoid sinus and the posterior ethmoidal cells. It drains into the upper nasal passage via the sphenoethmoidal recess.

The main function of the paranasal sinuses is controversially discussed. On the one hand, they reduce the weight of the skull, as the cavity formation saves bone material. On the other hand, their connection to the nasal cavity also ensures that the air we breathe is conditioned.

Five factors play a key role in maintaining the normal function of the paranasal sinuses:

• Unimpeded patency of the nasal cavity into the nasopharynx
• Patency of the natural openings to the paranasal sinuses
• Undisturbed function of the ciliated apparatus (ciliated epithelium)
• Quality and quantity of nasal secretions
• Maintenance of sterility in the paranasal sinuses (nitric oxide)

Norm variants can favour acute and chronic inflammation and cause intraoperative complications by narrowing outflow tracts. The most important anatomical variants include

• Septal deviation: single or S-shaped configuration. Often accompanied on the concave side by hyperplasia of the middle turbinate. Possible consequences are olfactory disorders and impaired ventilation of the nasal cavities or paranasal sinuses.
• Concha bullosa: Pneumatisation of the middle turbinate. Can lead to obstruction of the middle nasal passage.
• Agger nasi cells: anterior ethmoidal cells which, like supraorbital ethmoidal cells, can constrict the outflow tract of the frontal sinus
• Haller cells: infraorbital ethmoidal cells that can displace the ethmoidal infundibulum like variants of the uncinate process
• Onodi cells: ethmoidal cells located craniolaterally to the sphenoidal sinus. Close positional relationship to the optic nerve and the internal carotid artery.

Conventional radiological diagnosis[Bearbeiten]

In the radiological diagnosis of the paranasal sinuses, conventional X-ray examination only plays a subordinate role. It is only used to assess the maxillary sinus or frontal sinus in the context of rhinosinusitis.

Computed tomography[Bearbeiten]

Computed tomography (CT) is the method of choice for uncomplicated inflammatory and traumatic changes. It is also used in addition to magnetic resonance imaging (MRI) for neoplastic processes in order to visualise osseous involvement.

In most cases, native imaging is sufficient. If inflammatory or tumorous involvement of neighbouring structures is suspected, contrast-enhanced CT can be considered as an alternative to MRI.

See main article: Paranasal sinus CT

Magnetic resonance imaging[Bearbeiten]

MRI is preferably used to assess neoplastic or unclear soft tissue findings in the paranasal sinuses and to detect infiltration of neighbouring structures. Contrast medium is usually administered. The examination protocols generally include thin-layer sequences in T1 and T2 weightings as well as fat-saturated sequences (e.g. STIR). Diffusion-weighted sequences help to differentiate between tumour tissue and inflammatory changes.

PET-CT[Bearbeiten]

After resection or radiotherapy of neoplastic processes of the nasal cavity and paranasal sinuses, PET-CT helps to differentiate between tumour residue, recurrence and post-therapeutic changes.

Diseases of the paranasal sinuses include, among others:

• Inflammation
  • Acute rhinosinusitis (ARS)
  • Chronic rhinosinusitis (CRS) incl. polyposis nasi and mucoceles
• Fungal infections: e.g. mycetoma
• Granulomatosis with polyangiitis
• Fractures: e.g. Le-Fort fractures, blow-out fractures
• Benign neoplasms: e.g. osteoma, papilloma
• Malignant neoplasms: squamous cell carcinomas, adenocarcinomas, adenoid cystic carcinomas, aesthesioneuroblastomas, sinunasal undifferentiated carcinomas, sinunasal neuroendocrine carcinomas

• Image source podcast: © Diana Polekhina / Unsplash