Sinus CT Scans

8/3/2019 Sinus CT Scans

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Sinus CT Scans

Wellington S. Tichenor, M. D.

New York, New York

(212)517-6611

Because the images below are large files, sometimes they may be difficult to print.

The following is designed to enable you to develop a basic understanding of sinus anatomy as

well as CT scans, both normal and abnormal. We will review several CT scans, but start with adrawing to start to orient you.

There are four sets of sinuses: maxillary, ethmoid, frontal and sphenoid sinuses. We will

examine most of them in the following series of drawings and CT scans. The initial concepts area little difficult to understand, but will become clearer when we get to the CT scans.

LEGEND: F - Frontal sinuses, E - Ethmoid sinuses, M - Maxillary sinuses, O - Maxillary

sinus ostium, SS - Sphenoid sinus ST- Superior turbinate, T - Middle turbinate, IT-

Inferior turbinate, SM- Superior meatus, MM- Middle meatus, SR - Sphenoethmoidal

recess, S- Septum, ET - Eustachian tube orifice, A - Adenoids . Courtesy of Astra

Pharmaceuticals

In the first graphic representation, the three overlapping flaps of tissue, called turbinates (inferior- IT, middle - T, and superior - ST ) protect the openings of the sinuses, and allow

humidification, filtration and warming of air. The frontal (F) sinus is seen in this view, but is notusually involved to any great extent in sinusitis. The sphenoid sinus (SS) is also seen in this

view, and is sometimes involved in sinusitis. The sphenoid sinus drains into the sphenoethmoidalrecess (SR)

In the second graphic representation, the maxillary sinuses (M) drain through the maxillary sinusostia (O) into the middle meatus (MM). It should be noted that in this graphic diagram, the

opening at O appears to be extremely large. In actuality, it is the size of a pin head and actuallyfollows a rather circuitous route as you will see on the CT scans which follow. The ethmoid

sinuses (E) drain into both the middle meatus as well as into the superior meatus (SM).

The middle meatus (MM) is bounded by the middle turbinate (T) and the inferior turbinate (IT).(There is also a superior turbinate (ST), but that is relatively unimportant.)

Another important structure is the "ostiomeatal unit" which is the outflow tract from the sinuses

and includes the ostium of each sinus as well as the meati. When blocked, the ostiomeatal unitcan cause obstruction of the sinuses, analogous to putting a plug in a bathtub.


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The frontal sinuses (F) are occasionally important, but will not be dealt with to any great extentin this discussion. The septum (S) creates a barrier between the two sides of the nose. If it is

deviated to a great enough extent, an obstruction can occur. Occasionally, there may be aperforation (hole) in the septum, which can cause problems with the architectural support of the

nose.

The first CT scan is relatively normal:

LEGEND: + - border of maxillary sinus, * - maxillary sinus ostium, U - uncinate process, E

- ethmoid sinuses, IT- inferior turbinate, MT- middle turbinate, S - septum, C - concha

bullosa.

Note that the CT scan is a computerized X-Ray taken in the same way as the first diagram is

drawn, as if you were able to look head on into the sinuses. Note that the patient's right side is onyour left as indicated by the "right" mark in the upper left hand corner.

On the CT scan, bone appears white, air appears black, and soft tissue, fluid, or muscle is varyingshades of gray. Of note in the bottom portion of the scan is a ray pattern emanating from theteeth. This is as a result of poor penetration of the x-rays through the metal in the teeth.

When we evaluate the sinuses for sinusitis, we look for thickening of the lining of the sinus. Noteon the patient's left side (your right) at the + sign, there is a very sharp distinct border between

the black air in the maxillary sinus and the white bone. As you will see later, sinusitis ismanifested by grayish thickening of the lining of the sinus.

The asterisk (*) is at the point where drainage occurs from the maxillary sinus into the nose

through part of the ostiomeatal unit. The maxillary sinus ostia is bounded below by the uncinate

process (U) and above by the lower bony portion of the ethmoid sinuses (E). A narrowing in thisarea obviously can be very critical. The ethmoid sinuses, as can be seen, are much smaller thanthe maxillary sinuses.

On the right side (your left), one can see the middle turbinate (MT) as well as inferior turbinate

(IT). There is a slight deviation of the septum (S) to the right side (your left), but in this case it isunlikely that it is causing any obstruction. Of note is that there is air contained in the middle

turbinate on the left (C-short for concha bullosa). This represents a normal anatomical variant in


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which the ethmoid sinuses have pushed down into the middle turbinate. In this case, it does notappear to have caused a problem, but often it will cause a significant enlargement of the middle

turbinate and consequently an obstruction on one side of the nose.

The next CT scan is from a patient with significant sinus disease.

LEGEND: M - maxillary sinus, + - thickening of the maxillary sinus, E - ethmoid sinuses, P- polyp, O - maxillary sinus ostium, * - middle meatus.

Attention should first be directed to the + sign on the right side. Compared to the previous scan,there is a significant amount of grayish thickening between the white bone and the black sinuses.

Any thickening over 3 mm is definitely abnormal. Note that this thickening involves almost theentire maxillary sinus on both sides, but more so on the right side.

Compare the area on the right side where the maxillary sinus ostium (O) was observed on the

previous CT scan. There is no opening now, only the gray tissue completely blocking the ostium.Not surprisingly, this patient had a great deal of pain as a result of that blockage. Although there

is more thickening of the sinus lining on the right, there is more room to breathe through the noseon the right side (*) than on the left side. This is largely as a result of the deformity of the middle

turbinate, located just above the asterisk (compare to the opposite side). This may havecontributed to the sinus disease in this case, causing obstruction of the ostiomeatal unit. Not

surprisingly the ethmoid sinuses were involved as well. The ethmoid sinuses are either filledwith polyps (P) or the lining is thickened. There is very little air left in the ethmoid sinuses (E).

This X-Ray is from another patient with fairly severe sinus disease:


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LEGEND: MT- middle turbinate, IT- inferior turbinate, P - polyp or cyst, E - ethmoid

sinuses, O - maxillary sinus ostium, * - frontal sinus .

As compared to the previous x-ray, this patient has larger polyps or cysts (P) (it is often difficult

to tell the difference on CT scan) on the right side, with significant obstruction of the ostium. On

the left side the ostium (O) cannot be clearly seen, but you get the idea of where it's supposed tobe. The ethmoid sinuses (E) on the right side are completely obstructed, being filled with eitherpolyps, cysts or thickening of the sinuses. On the left side, there is some thickening, but as you

can see, for the most part the ethmoid sinuses are fairly clear. The asterisk on the left siderepresents the point at which the ethmoid sinuses merge into the frontal sinuses. Note the

difference in size between the middle turbinate (MT) on the right and left side, and also theinferior turbinates (IT) on each side.

This CT scan was done after surgery was performed on the patientwhose CT scan you just reviewed.

LEGEND: E - Ethmoid sinuses, O - maxillary sinus ostium, M - maxillary sinuses, S -septum, MT - middle turbinate, IT - inferior turbinate.

That's pretty impressive isn't it ?, even if you're a lay-person. As you can see, the polyps that

were previously in the maxillary sinus (M) are now gone and the opening at the maxillary sinusostia (O) is wide open, having had the uncinate process removed. The ethmoid sinuses (E) on

both sides have been cleaned out. The surgery which was performed did not involve extensiveremoval of the lining of the sinuses. Just opening them up and allowing them to "breathe" is

often enough to prevent severe disease. Of note, however, is the fact that this patient still doesn'thave a normal nasal airway. (Compare to the first CT scan. Note the size of the black area next to

the middle turbinate (MT) and inferior turbinate (IT).) In addition to having sinus problems, this

patient also has allergy problems which had to be treated in order to prevent future nasalproblems and sinus disease.

We hope that the short course on X-Rays of the sinuses has been helpful in understand a littlemore about sinusitis.

Imaging Techniques


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Computer Tomography. Computed tomography (CT) scanning is the best method for viewing the

paranasal sinuses. There is little relationship, however, between symptoms in most patients and findings

of abnormalities on a CT scan. CT scans are recommended for acute sinusitis only if there is a severe

infection, complications, or a high risk for complications. CT scans are useful for diagnosing chronic or

recurrent acute sinusitis and for surgeons as a guide during surgery. They show inflammation and

swelling and the extent of the infection, including in deeply hidden air chambers missed by x-rays and

nasal endoscopy. Often, they can detect the presence of fungal infections.

X-Rays. Until the availability of endoscopy and CT scans, x-rays were commonly used. They are not as

accurate, however, in identifying abnormalities in the sinuses. For example, more than one x-ray is

needed for diagnosing frontal and sphenoid sinusitis. X-rays do not detect ethmoid sinusitis at all. This

area can be the primary site of an infection that has spread to the maxillary or frontal sinuses.

Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) is not as effective as CT in defining the

paranasal anatomy and therefore is not typically used to image the sinuses for suspected sinusitis. MRI

is also more expensive than CT. However, it can help rule out fungal sinusitis and may help differentiate

between inflammatory disease, malignant tumors, and complications within the skull. It may also be

useful for showing soft tissue involvement.

http://www.umm.edu/patiented/articles/how_sinusitis_diagnosed_000062_6.htm

Penegakan diagnosis sinusitis kronik yang terbaik ialah dengan menggunakan pencitraan

radiologis. Rontgen thorax yang biasa dapat menunjukkan penebalan mukosa sebagai tandasinusitis. Ketinggian fluida udara jarang ditemui di kasus sinusitis kronis. Ditambah lagi,

pemeriksaan ini tidak mampu menggambarkan sinus yang lebih dalam, misalnya sinus etmoid

dan kompleks osteomeatal.

Pemeriksaan yang baik ialah dengan CT-scan sinus. CT terpaksa dikerjakan kalau pasien dirasatidak respon terhadap terapi atau sebagai persiapan operasi. CT Scan koronal dapat

menggambarkan posisi anatomis dengan baik untuk persiapan operasi. Dengan CT Scan jugadapat terlihat letak-letak obstruksi secara tajam dan akurat. CT scan bahkan mampu mendeteksi

entitas spesifik dalam hidung semacam aspegilloma. Sedangkan kerabatnya, MRI, tidak terlalusering dilakukan karena mahal. Namun sebenarnya MRI baik untuk melihat kontras jaringan

lunak serta mendeteksi massa seperti neoplasma, komplikasi kranial dan intraorbital, sertasinusitis akibat jamur.

Role of X-rays in rhinology

By


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Dr. T. Balasubramanian M.S. D.L.O.

Paranasal sinuses are air containing chambers surrounding the nasal cavity. Pathology

involving the sinuses, may present on the radiograph as alterations in the translucency of

the sinuses. Some pathological conditions affecting the para nasal sinuses may produce

fluid hence effort should be made to demonstrate this fluid level. This is possible if the

radiograph is taken in erect position allowing a clear air fluid level to be visualised in the

radiograph.

Standard positions of sinus radiographs:

Radiographic positions to study the paranasal sinuses are standardised around three

positions:

1. Two anatomical - namely cornal and sagittal

2. One radiographic - termed as radiographic base line. This line represents a line drawn

from the outer canthus of the eye to the mid point of the external auditory canal.

The various radiographic positions used to study paranasal sinuses are:

1. Occipito-mental view (Water's view)

2. Occipital-frontal view (Caldwel view)

3. Submento-vertical position (Hirtz position)

4. Lateral view

5. Oblique view 39 Degrees oblique (Rhese position)

Occipito mental view: This is also known as the Water's view. This is the commonest view

taken to study the paranasal sinuses. The patient is made to sit facing the

radiographic base line tilted to an angle of 45 degrees to the horizontal making the sagittalplane vertical. The radiological beam is horizontal and is centered over a point 1 inch

above the external occipital protruberance. In obese patients with a short neck it is

virtually impossible to obtain an angulation of 45 degrees. These patients must be made to

extend the neck as much as possible and the xray tube is tilted to compensate for the

difference in angulation. The mouth is kept open and the sphenoid sinus will be visible

through the open mouth. If the radiograph is obtained in a correct position the skull shows

a foreshortened view of the maxillary sinuses, with the petrous apex bone lying just


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beneath the floor of the maxillary antrum. In this view the maxillary sinuses, frontal

sinuses and anterior ethmoidal sinuses are seen. The sphenoid sinus can be seen through

the open mouth.

Diagram showing the position of the skull while taking x-ray sinuses water's view

If the antrum in water's view demonstrates a loss of translucency which could be an

indicator of fluid level, then another x ray is taken with a tilt of saggital plane to an angle of30 degrees. This view will clearly demonstrate movement of fluid to a new position. In this

view the fluid moves towards the lateral portion of the antrum where it can clearly be seen.


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Xray paranasal sinuses water's view


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In x ray para nasal sinuses waters view the normal frontal sinus margins show scalloping.

Loss of this scalloping is a classic feature of frontal mucocele. If frontal sinus is congenitally

absent (agenisis) then a suture line known as the metopic suture is visible in the fore head

area. Sometimes a pair of large anterior ethmoidal air cells may take up the place of frontal

sinuses. Here too the metopic suture line is visible. This suture divides the two halfs of

frontal bone of the skull in infants and children. This suture line usually disappears at the

age of 6 when it fuses. If this suture is not present at birth it will cause a keel shaped

deformity of the skull (trigonocephaly).


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Xray paranasal sinuses showing metopic suture

Since hypoplastic antra are associated with sclerosis of its margins, it will be very difficult

to perforate the medial wall of the antrum while performing antrostomy.

In conditions like malignancy involving the maxillary antrum X ray sinuses waters view

shows the following features:

Expansion

Erosion

Opacity.


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Expansion is characterised by increase in the size of maxillary antrum when compared to

its counter part on the opposite side.

Erosion may occur in the medial wall of the antrum or in its antero lateral wall. The canine

fossa area is the thinnest portion of maxillary antrum antero lateral wall. Erosion is hence

common in this area.

Opacity is the term used to describe a maxillary sinus antra involved with malignant

growth. This opacity is due to the periosteal reaction due to malignant growth.

Xray sinuses showing malignant growth in the right maxilla

Occipito frontal view (Caldwell view): This position is ideally suited for studying frontal

sinuses. In this position the frontal sinuses are in direct contact with the film hence there is

no chance for any distortion or geometric blur to occur.


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Figure showing the skull position in Caldwell view xray

To get a caldwell view the patient is made to sit in front of the film with the radiographic

base line tilted to an angle of 15 - 20 degrees upwards. The incident beam is horizontal and

is centered 1/2 inch below the external occipital protruberance. This view is also known as

the frontal sinus view.

Submentovertical view: is primarily taken to demonstrate sphenoid sinuses. Fluid levels in

sphenoid sinuses are clearly shown in this view. To take an x ray in this position, the back

of the patient is arched as far as possible so that the base of skull is parallel to the film. The

x ray beam is centered in the midline at a point between the angles of the jaws. In elderlypatients this view can be easier to achieve if carried out in the supine position with the head

hanging back over the end of the table. This view also demonstrates the relative thicknesses

of the bony walls of the antrum and the frontal sinuses.


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Figure showing the skull position in submentovertical view

Lateral view:

This view helps in distinguishing the various pathologies involving the frontal sinuses. It

helps in determining whether the loss of translucency is due to thickening of the anterior

bony wall or infection of the frontal sinus per se. This view also demonstrates fluid levels in

the antrum. This view also gives information on the naso pharynx and soft palate. This is

infact a standard projection used to ascertain enlargement of adenoid tissue.

Xray skull lateral view

For this view the patient is made to sit with the sagittal plane parallel to the xray film and

the radiographic base line is horizontal. The incident ray is horizontal and the incident

beam is centered at the mid point of the antrum.


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Figure showing skull position for xray skull lateral view

Oblique view:

This view helps in demonstrating posterior ethmoid air cells and optic foramen. To obtain

this projection the patient is made to sit facing the film. The head is rotated so that the

sagittal plane is tured to an angle of 39 degrees. The radiographic base line is at an angle of

30 degrees to the horizontal. The incident beam is horizontal and is centered so that the

beam passes through the centre of the orbir nearest to the film.

With the advent of CAT scan these modalities of imaging are slowly losing their relevance.

Sinus CT Scans

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