SINUSES
LEARN
Lined w/ Schneiderian epithelium (cilated mucosa of ectodermal origin) that propels contents along anatomic drainage pathways towards the nasopharynx.
Sinuses develop at different times in children.
At birth, maxillary and ethmoid sinuses are present but hypoplastic.
Later the sphenoid and then frontal sinus pneumatizes
Superior, middle and inferior nasal turbinates/conchae are 3 paired bony protuberances w/n the nasal cavity that form air passages inferior to each called meatuses.
Inferior meatus is the drainage site of the nasolacrimal duct.
Ostiomeatal unit is common pathway for the maxillary, frontal, and anterior ethmoid sinuses to drain into the middle meatus. Consists of:
Maxillary sinus ostium, ethmoid infundibulum, uncinate process, ethmoid bulla, hiatus semilunaris, and middle meatus.
Frontal sinus drains via frontal recess either into ethmoid infundibulum or directly into the middle meatus.
Maxillary sinus (largest) drains via maxillary sinus ostium and infundibulum. If obstructed can cause isolated maxillary sinus disease.
Ethmoid sinus/air cells are divided into anterior and posterior air cells by the basal lamella of the middle turbinate where it attaches to the lamina papyracea.
Lamina papyracea: thin part of ethmoid bone separating ethmoid air cells from orbit.
Ethmoid labyrinth is covered superiorly by the fovea ethmoidalis, an extension of the orbital part of the frontal bone.
B/n the oribtal plates on either side are the cribiform plates, the horizontal portion of the ethmoid bone that lies lower than the fovea ethmoidalis and supports the olfactory bulbs.
Sphenoethmoidal recess is common pathway for the sphenoid sinus and posterior ethmoid air cells to drain into the superior meatus.
Anterior skull base is comprised of the orbital parts of the frontal bone, cribiform plates of ethmoid bone, and planum sphenoidale and lesser wings of the sphenoid bone. Separates the anterior cranial fossa from the sinonasal tract and orbits.
ANATOMIC VARIANTS
Agger nasi cell: anterior most ethmoid air cell located anterior to the frontal recess. A larger agger nasi cell can narrow the frontal recess.
Supraorbital cell is an anterior ethmoid cell that extends superior to the orbit and anterior ethmoid notch that carries the anterior ethmoid artery.
The presence of supraorbital pneumatization places the artery at greater intraoperative risk.
Haller (infraorbital) cell is an ethmoid air cell located along the medial orbital floor which can narrow the maxillary ostium if enlarged or inflamed.
Onodi (sphenoethmoidal) cell is a posterior most ethmoid air cells that extends superior and lateral to the sphenoid sinus. Onodi cell should be identified to avoid intraoperative damage to the adjacent optic nerve.
CT is primary modality for imaging the bony detail of the sinuses. Imaging is usually not appropriate for acute uncomplicated rhinosinusitis but is indicated for suspected orbital or intracranial complications of acute rhinosinusitis, suspected invasive fungal sinusitis, surgical planning for chronic or recurrent acute rhinosinusitis or suspected sinonasal mass.
Must identify anatomic variations that can lead to surgical complications.
MRI is usueful for ST contrast in evaluating suspected orbital or intracranial complications of sinusitis or a sinonasal mass. WHile both may appear as sinusopacification on CT, contrast enhancement on MRI clearly distinguishes mucosal lesions from obstructed secretions.
Thinning or bony dehiscence (absence of bone) 2/2 prior injury or chronic inflammation should be identified, particularly at the cribiform plate (anterior cranial fossa), lamina papyracea (orbit), and sphenoid sinus walls (carotid canal and optic nerve).
INFLAMMATORY SINUS DISEASE
RHINOSINUSITIS
Inflammation of the paranasal sinuses and nasal mucosa.
Sinus mucosal thickening is a common but nonspecific imaging finding.
Clinical diagnosis based on sx such as purulent nasal drainage, nasal obstruction, facial pressure and hyposmia.
RF
Mucociliary clearance defects: CF, primary ciliary dyskinesia
Immunodeficiencies: CVID, hypogammaglobulinemia
Small vessel vasculitides: granulomatosis w polyangiitis especially when there is bony erosion or septal perforation, and eosinophilic granulomatosis with polyangiitis especially when there is nasal polyposis.
Acute < 4 weeks
MCC is viral followed by bacterial infection
Acute sinusitis is more likely to feature an air-fluid level and bubbles w/n the fluid.
Chronic >=12 consecutive weeks
Chronic sinusitis is probably related to obstruction of sinonasal drainage pathways. The goal of functional endoscopic sinus surgery is to open/widen those pathways.
Sclerotic thickening of sinus walls, due to prolonged mucoperiosteal inflammation is characteristic of chronic sinusitis.
Odontogenic sinusitis: MCC of unilateral/isolated maxillary sinusitis. The usual etiologies are a maxillary premolar or molar tooth w/ periapical abscess or, after extraction, an oroantral fistula.
FUNGAL RHINOSINUSITIS
COMPLICATIONS OF RHINOSINUSITIS
SINONASAL INFLAMMATORY POLYPS
PARANASAL SINUS RETENTION CYST
Retention cysts are well-defined rounded collections of mucous or serous fluid arising in the sinus lining due to obstruction of small seromucinous glands.
Mucous retention cysts is often used generically to include both mucous and serous retention cysts.
Typically as but can obstruct sinus drainage pathways. They are most commonly located in the maxillary sinus.
Expanded chronically obstructed sinus lined by normal respiratory epithelium and completely filled w mucoid secretions due to drainage obstruction.
Mucocele may be 2/2 inflammatory sinus disease (most commonly) or tumor .
2 types
Internal: herniation of cyst into submucosal tissue adjacent to sinus bony wall
External: herniation of cyst through bony wall w extension into subcutaneous tissue or intracranial cavity.
Imaging:
Complete opacification of a single sinus cavity w expansile remodeling and thinning of the bony walls. The sinus contents tend to appear homogeneous on CT and MR, however, the MR SI is variable depending on the degree of desiccation.
If peripheral enhancement -> mucopyocele, if central enhancement -> tumor
Frontal (60-65%) > ethmoid (25%) > maxillary (5-10%) > sphenoid (2-5%)
Frontal: expands anteriorly into skin of forehead or posteriorly into anterior cranial fossa
Ethmoid: thins & remodels lamina papyracea (lateral ethmoid air cell wall), bowing it into orbit.
Maxillary: expands into ipsilateral nasal cavity, usually in area of secondary ostium of maxillary sinus or into premaxillary STs
Sphenoid: expands anterolaterally into posterior ethmoids and orbital apex.