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Paranasal Sinuses: Radiological Anatomy

Dr. Hazem Abu Zeid YousetDecember 2006

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What are the sinuses? The sinuses are chambers in the bones of the face and skull that are normally lined with a thin mucosa. They communicate with the nasal cavity via narrow openings. Air and mucus enter and exit to and from the sinuses through these openings.

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Function of Paranasal Sinuses

Humidifying and warming inspired airRegulation of intranasal pressureIncreasing surface area for olfactionLightening the skullResonanceAbsorbing shockContribute to facial growth

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OVERVIEWEach patient's sinus anatomy has a unique configuration, and it is vital that this is well delineated for surgery to be successful. The four paired paranasal sinuses are the ethmoid, maxillary, frontal, and sphenoid sinuses. These are named after the cranial bones in which they are located. The sinuses normally contain air

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TECHNIQUES OF SINUS EXAMINATION(1)PLAIN RADIOGRAPHY.(2)HRCT.(3)MRI.(4)US.

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WATERS VIEW

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HRCT

PrerequisitesHigh tube voltage kVpHigh mAsThin slicePitch 1:1Reconstruction bone algorithm

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THE ETHMOID AIR CELLS

The ethmoid sinuses are the sinuses "between the eyes." They are typically fully developed by age 12. They are like a honeycomb, consisting of multiple small sinus (usually 12-15 on each side) that are separated by thin bony septa cells that together form the ethmoidsinus.

At birth, usually three or four ethmoid cells are present. However, they are difficult to recognize on x-rays until the infant reaches about six months of age. Only the ethmoid and maxillary sinuses are significantly developed enough at birth to be clinically significant. (Significant growth of the sphenoid and frontal sinuses are rarely seen until three years of age.)

The lateral or sidewall of the ethmoid sinus is called the "lamina papyracea,"

10 Pediatric Sinuses

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The upper border of the ethmoid sinus is called the fovea ethmoidalis, or "ethmoid roof." The fovea ethmoidalis is a part of the skull base and separates the ethmoid sinus from the brain. Medially along the roof of the ethmoid sinus is the thinner bone of the cribriform plate that separates the nasal cavity from the brain. The cribriform plate tends to lie 2-3mm lower than the fovea ethmoidalis.

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The ethmoid sinus can be thought of as having two distinct groups of sinus cells. The anterior group drains into a space called the middle meatus, and the posterior group drains into a space called the superior meatus. The anterior and posterior ethmoid cells are divided by a plate of bone called the "basal lamella" or "ground lamella."

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The anterior ethmoid cells can be further sub-divided intoa) frontal recess cells, the most anterior and superior communicates with the frontal sinusb) Haller cells, on the lateral wall of the inf. c) agger nasi cells, “anterimost” immediately anterior and superior to the insertion of the middle turbinatesd) bulla cells, is the largest and most constant air cell of the anterior ethmoid complex “above and posterior to the infundibulum”e) conchal cells. pneumatization of the middle turbinate.

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The ethmoid infundibulum represents a cleft or space through which a number of the sinuses (the frontal, maxillary, and anterior ethmoid) drain. Therefore, it is an important "major intersection." The boundaries of this space are formed anteriorlyby the uncinate process, laterally by the lamina papyracea, and in the back posteriorly by the ethmoid bulla. The ethmoid infundibulum opens into the middle meatus .

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The posteriort ethmoid air cells are larger but have a smaller total area than the anterior cells.Behind the ground lamella of the MTOnodi cells “the most posterior cell” superolateral to the sphenoid sinus.

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The maxillary sinusesPea sized and fluid filled at birth, it undergoes two rapid growth spurts. The first is between birth and age three years and the second is between age seven and 18. The sinus becomes adult size by adolescence.

The drainage pathway or ostium of the maxillary sinus is located in the superior and anterior part of the medial wall of the maxillary sinus. Through this ostium the maxillary sinus communicates with the nose. Specifically, mucus drains from the maxillary sinus into the infundibulum in the middle meatus and out into the nose.

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The roof of the maxillary sinus is also the floor of the orbit. The floor of the maxillary sinus is formed by the maxillary bone; specifically, a part called the "alveolar process." The roots of the first and second molar teeth and the second bicuspid teeth often project through the floor of the maxillary sinus, where they are covered only by the thin mucus membrane within the sinus. The anterior or front wall of the maxillary sinus separates the sinus from the cheek skin, while the posterior or back wall separates the sinus from a space filled with blood vessels and nerves. The upper part of this space is called the infratemporal fossa, and the lower part is called the pterygomaxillary space.

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The frontal sinusesThey are not clinically perceptible at birth. The frontal sinuses can rarely be demonstrated on plain x-ray before two years of age. Growth of the frontal sinuses is typically complete by about age 20. About 5% of the population fails to develop one or both frontal sinuses. The frontal sinus has anterior and posterior bony walls. The front wall separates the sinus from the forehead soft tissue and skin. The back wall separates the sinus from the brain. The front wall is approximately twice as thick as the back wall. The frontal sinus is usually divided into two sides by a very thin bony divider. The mucus from the frontal sinus drains out a small channel called the frontal recess, into the infundibulum, then into the upper part of the middle meatus, and out into the nose.

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The sphenoid sinusThe sphenoid sinus is not perceptible at birth. Further significant growth does not begin until a child is three years of age. Pneumatization and growth usually becomes rapid after seven years and reaches adult size by 12-15 years. The left and right sphenoid sinuses are separated by a thin bony partition. The sphenoid sinuses are usually asymmetric. The sphenoid sinus drains into the nose through the sphenoid ostium into a space called the sphenoethmoid recess, and out into the nose.Several important structures occupy positions in relationship to the

sphenoid sinus. Importantly, the optic nerve and pituitary gland are above the sphenoid, and the pons is just behind the sphenoid. The internal carotid arteries are just to the side of the sphenoid sinus. The cavernous sinus is also found to the side of the sphenoid sinus.In half of the population, the internal carotid artery forms a visible

indentation in the side wall of the sphenoid sinus. The bony wall is not always complete, so great care must be taken when performing sphenoid surgery.

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The osteomeatal complexThe "grand central station" of the sinuses is the osteomeatal complex -- the most important sinus opening. Any process that causes blockage in this sensitive area can occlude the other sinuses that drain into the osteomeatal complex.The OMC is bounded medially by the middle turbinate, posteriorly and superiorly by the basal lamella, and laterally by the lamina papyracea. Inferiorly and anteriorly the OMC is open. This anatomic region therefore includes the anterior ethmoid sinus, ethmoid bulla, frontal recess, uncinateprocess, infundibulum, hiatus semilunaris, and middle meatus.

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Thank you