Ct Scan Sinus Paranasal.docx

Anatomy Nasal structures The osseocartilaginous septum forms the medial extent of the nasal cavity, and deviations in its position can be of clinical significance. The inferior turbinate extends along the inferior lateral nasal wall posteriorly toward the nasopharynx. In patients with a significant allergic component to their symptoms, the inferior turbinates may be enlarged. Enlarged turbinates may be obscured on CT scanning and should be correlated with physical examination findings. The nasolacrimal duct (NLD) opens into the inferior meatus underneath the inferior turbinate. The NLD drains the lacrimal sac and runs within a bony canal formed by the maxilla, lacrimal apparatus, and inferior turbinate bones. Because of this location, a large duct can be mistaken for obstruction within the ostiomeatal unit. The middle turbinate has 3 anatomic parts and is a key landmark in endoscopic sinus surgery. The anterior third courses vertically, lying in the sagittal plane, running from posterior to anterior. Superiorly, the middle turbinate attaches to the skull base at the lamina cribrosa of the cribriform plate. The middle third turns coronally and laterally to insert on the lamina papyracea. The coronal component of the middle turbinate is referred to as the basal lamella, and it represents the dividing point between the anterior and posterior ethmoid air cells. The posterior portion of the middle turbinate becomes horizontal and posteroinferiorly attaches to the lateral nasal wall.

The uncinate process This hook-shaped bone of the lateral nasal wall forms the anterior border of the ethmoid infundibulum, which leads to the natural ostium of the maxillary sinus. Anteriorly, the uncinate process attaches to the lacrimal bone, and inferiorly, the uncinate process attaches to the ethmoidal process of the inferior turbinate. The posterior edge lies in the hiatus semilunaris inferioris. Superiorly, the uncinate process may attach to the middle turbinate, the lamina papyracea, and/or the skull base. See the image below. [1]

Coronal view demonstrating the blockage of the ostiomeatal complex by a large concha bullosa (CB). Important components of the ostiomeatal complex that can be seen include the uncinate process (U) and maxillary sinus ostium (MO). The attachments of the middle turbinate (MT*) to the cribriform plate (cb) and of the uncinate process (U*) to the skull base can be appreciated. The fovea ethmoidalis (fv) and crista galli (^) can also be seen. Image used with permission from A. John Vartanian, MD.

Ethmoid air cells The ethmoid sinus consists of approximately 7-15 cells with a variable pneumatization pattern. The ethmoid bulla is the most constant landmark and forms the most anterior ethmoidal air cell. The lateral extent of the bulla is formed by the lamina papyracea. The basal lamella of the middle turbinate separates the anterior ethmoid cells from the posterior ethmoid cells. Anterior ethmoid cells drain into the middle meatus, while posterior cells drain into the superior meatus. The anterior ethmoid cells are an important part of the ostiomeatal unit. Obstruction here can also affect frontal and maxillary sinus drainage. Other cells that may originate from the ethmoid cell development include frontal cells, supraorbital ethmoid cells, infraorbital cells (ie, Haller cells), and sphenoethmoid cells (ie, Onodi cells).[3] The suprabullar recess is a potential air space that can exist between the ethmoid bulla and the skull base.

Sphenoid sinus

The sphenoid sinus is the most posterior paranasal sinus. It is found superior to the nasopharynx, just anterior and inferior to the sella turcica and posterior to the posterior ethmoid cells. The sphenoid ostium can be seen medial to the superior turbinate and posterior to the basal lamella. An intersphenoid septum variably divides the sphenoid into 2 air cells. Several important structures are related to the sphenoid sinus. The internal carotid artery is typically found at the posterolateral wall of the sphenoid sinus. In up to 22% of cases, this bony covering may be dehiscent. The optic nerve and its bony encasement produce an anterosuperior indentation within the roof of the sphenoid sinus. In 4% of cases, the bone surrounding the optic nerve is dehiscent. See the image below.

Close-up coronal view of the sphenoid sinus with dehiscence of the sellar floor. Image used with permission from A. John Vartanian, MD.

The frontal sinus outflow tract (frontal recess) The frontal sinus outflow tract is a tortuous path that leads from the frontal sinus into the nasal cavity. The ethmoid bulla often defines and limits the posterior aspect of the frontal sinus outflow tract. Anteriorly, the frontal sinus outflow tract is bordered by the agger nasi cells and, in some cases, the uncinate process. The lateral wall of the frontal recess is bounded by the lamina papyracea. The medial boundary is the middle turbinate. Posteriorly, the frontal recess is bordered by the anterior wall of the ethmoid bulla. This area is affected

by the development of anterior ethmoid cells, such as the frontal or supraorbital cells. Enlargement and/or disease of any of the cells within the frontal sinus outflow tract may contribute to the blockage of the frontal sinus.

Disease States CT scanning can be helpful in the diagnosis of acute and chronic sinusitis, neoplastic and inflammatory processes, and other problems (eg, congenital anomalies). Acute sinusitis is caused by bacterial or fungal infections usually secondary to an obstructed sinus cavity. Structural anatomic variations, acute edema of sinonasal mucosa in response to infection or allergens, and compromise of nasociliary flow can all contribute to acute and chronic sinusitis. CT findings of sinus opacification, air-fluid levels, and thickened localized mucosa are all findings of acute sinusitis. Many nonspecific CT findings, including thickened turbinates (nasal cycle vs allergic process vs inflammation) or diffusely thickened sinus mucosa (allergic disease vs chronic sinusitis), may be associated with several sinonasal conditions.[5] In chronic sinusitis, repeated episodes of acute sinusitis or festering infection usually combined with unfavorable anatomic factors lead to a vicious cycle of infection, mucociliary incompetence, and chronic mucosal inflammation. CT findings suggestive of chronic sinusitis include mucosal thickening, opacified air cells, bony remodeling, and bony thickening due to inflammatory osteitis of the sinus cavity walls. Bony erosion can occur in severe cases, especially if associated with massive polyps or mucoceles. CT findings of bony destruction should alert the clinician to also consider less common diseases, such as sinonasal tumors or granulomatous disease processes. See the image below.

Axial image at the level of the inferior turbinates demonstrating maxillary mucoceles and mucosal thickening, especially in the right maxillary sinus. Image used with permission from A. John Vartanian, MD. Sinonasal polyps can create sinus disease by obstruction or mass effect and by causing secondary infections. Sinonasal polyps appear on CT scans as nodular or rounded masses and amorphous opacified blobs of tissue. Bony remodeling can occur, but it is typically subtle, which is expected from the usual slow growth pattern of sinonasal polyps and benign processes in general. See the image below

Axial images of the anterior and posterior ethmoid air cells. The presence of massive sinonasal polyps was confirmed by intraoperative findings. Image used with permission from A. John Vartanian, MD. Fungal sinusitis can be divided into invasive fungal sinusitis, chronic noninvasive fungal sinusitis (mycetoma), and allergic fungal sinusitis. Invasive fungal sinusitis due to mucormycosis or aspergillosis is typically a disease that affects immunocompromised patients and can have a fulminant course. Early in the disease process, opacification of sinuses is seen. Disease progression to a more fulminant state accompanies vascular invasion and localized destruction. Intracranial, cavernous sinus, and orbital complications may occur with advanced infections. CT findings mirror these processes with expanding localized destruction of bone. Mycetomas appear inside the sinus cavity as noninvasive balls of fungus. CT findings may include a localized sinus opacification, homogenous mass that does not change shape with head position (gravity), and a mass with presence of calcifications (found in 25% of cases).

Allergic fungal sinusitis (AFS) may occur in atopic patients as a hypersensitivity reaction to fungal antigens. Many patients with AFS may also have various degrees of nasal polyposis. On CT scans, heterogeneous opacification can be seen with a typical pattern of central hyperdense areas of opacification surrounded by less dense areas of opacification. Calcified areas can sometimes be seen. Bony expansion, remodeling, and even diffuse bony destruction can be seen in advanced cases. With experience, CT findings can be accurately correlated with anatomic and clinical realities of the particular patient. As for all radiologic surveys, sinus CT scans must be read with a systematic approach. After the primary survey of the CT scan is completed, including patient name, indications for the CT scan, type of scan, cross-sectional view being discussed, and major radiologic findings, particular attention is directed toward potential "bottle-neck" areas, where normal passages may be occluded by disease states or variant anatomy. A systematic approach is helpful when interpreting CT scans. Reading the CT scan from anterior to posterior (on coronal views) or from top to bottom (on axial sections) can help organize one's approach in analyzing structures to be interpreted. For initial orientation, a number of important paranasal sinus structures are identified, including the frontal sinuses, the frontal recess, the agger nasi cells, the anterior ethmoidal sinus cells, the ethmoid roof, the ethmoidal bulla, the uncinate process, the ethmoidal infundibulum, the maxillary sinus, the middle meatus, the nasal septum, the turbinates, the basal lamella, the posterior and anterior ethmoid cells, and the sphenoid sinus. See the image below.

Coronal view demonstrating well-pneumatized frontal sinuses (FS), the ethmoid bulla (b), and the lamina papyracea (LP). Also of interest is the presence of an aerated middle turbinate or concha bullosa (c) blocking the ostiomeatal complex. The inferior turbinate is labeled IT. Image used with permission from A. John Vartanian, MD. If the CT scan is being read as a prelude to surgery, a number of additional anatomic and structural features need to be considered. The thickness, orientation, and most medial position of the lamina papyracea must be noted. Any dehiscences or excessive medial bowing of this thin bone should be noted prior to surgery. Similarly, the depth of the olfactory fossa must be recognized. The relationship of the sphenoid sinus and posterior ethmoid air cells vis a vis the internal carotid artery and optic nerves should be noted.

Important Radiologic Anatomic Landmarks Landmarks on coronal CT sections  

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Relationship of cells within the frontal recess and their relationship to the frontal sinuses Depth of the olfactory fossa: The deeper the fossa (ie, increased distance from the cribriform plate and the fovea ethmoidalis), the higher the chance for fracture or perforation with surgical maneuvers. Slope, thickness, and asymmetries in the height of the ethmoid roof o The prevalence of intracranial penetration during FESS is higher when this anatomic variation occurs. o Intracranial penetration is more likely to occur on the side with the lower roof. Patency of the ostiomeatal complex

Coronal view demonstrating the blockage of the ostiomeatal complex by a large concha bullosa (CB). Important components of the ostiomeatal complex that can be seen include the uncinate process (U) and maxillary sinus ostium (MO). The attachments of the middle turbinate (MT*) to the cribriform plate (cb) and of the uncinate process (U*) to the skull base can be appreciated. The fovea ethmoidalis (fv)

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and crista galli (^) can also be seen. Image used with permission from A. John Vartanian, MD. Attachment of the middle turbinate Width of the infundibulum Vertical distance from the maxillary sinus to the ethmoid roof in posterior ethmoid cells Degree of pneumatization of the maxillary sinus Status of the lamina papyracea o Dehiscence in the lamina papyracea o Shape of the medial orbital wall Attachment of the uncinate process Alignment of the septum Size and status of the maxillary sinuses (hypoplastic vs normal size) Other variations, such as the presence of a concha bullosa

Landmarks on axial CT sections 

Depth and ratio of the anterior and posterior ethmoid cells compared to the sphenoid sinus (see the image below) o Degree of pneumatization of sphenoid sinus o Position of sphenoid intersinus septae

Axial images of the anterior (ae) and posterior (pe) ethmoid air cells. The sphenoid sinus (sp) can be seen with its intersinus septum. Image used with permission from A. John Vartanian, MD. Presence or absence of an Onodi cell (sphenoethmoidal cell) Dehiscence in the bony covering of the carotid artery or optic nerve o o

Relationship of the optic nerve to the posterior ethmoid cells The presence of anterior clinoid process pneumatization

Degree of indentation created by the carotid artery and optic nerve Position of uncinate (medial versus lateral) Patency of the ostiomeatal complex Patency of the V-shaped ethmoidal infundibulum Alignment of the septum DAFTAR PUSTAKA Aksoy EA, Özden SU, Karaarslan E, et al. Reliability of high-pitch ultra-low-dose paranasal sinus computed tomography for evaluating paranasal sinus anatomy and sinus disease. J Craniofac Surg. Sep 2014;25(5):1801-4. omovic S, Esmaeili A, Chan NJ, Choudhry OJ, Shukla PA, Liu JK, et al. High-resolution computed tomography analysis of the prevalence of Onodi cells. Laryngoscope. Jul 2012;122(7):1470-3. Minni A, Messineo D, Attanasio G, Pianura E, D'Ambrosio F. 3D cone beam (CBCT) in evaluation of frontal recess: findings in youth population. Eur Rev Med Pharmacol Sci. Jul 2012;16(7):912-8. Chakravarti A, Naglot S, Dhawan R. Outcome of endoscopic sinus surgery in patients with symptomatic chronic rhinosinusitis with minimal changes on computerised tomography. Indian J Otolaryngol Head Neck Surg. Oct 2011;63(4):359-63.

McLaughlin RB Jr, Rehl RM, Lanza DC. Clinically relevant frontal sinus anatomy and physiology. Otolaryngol Clin North Am. Feb 2001;34(1):1-22.