High-resolution sinus computed tomography and magnetic resonance imaging (MRI) allow for the depiction of normal sinus anatomy, as well as the visualization of sinus pathology. The author discusses chronic sinus disease, appropriate imaging techniques, the contribution of MRI in the patient with benign or inflammatory sinus disease, and the use of imaging in malignant sinus pathology.
Dr. Phillips is an Associate Professor in the Departments
of Radiology, Neurosurgery, and OtolaryngologyHead and Neck
Surgery; and the Director of the Division of Neuroradiology at
the University of Virginia Health System, Charlottesville, VA.
He is also a member of the editorial board of this
As has happened in all facets of neuroimaging, the introduction
and wide acceptance of cross-sectional imaging has changed the way
we "do business" in imaging the sinonasal structures. Our imaging
choices now are largely computed tomography (CT) or magnetic
resonance (MR) imaging to depict benign and malignant sinus
pathology. We have moved away from the relatively subtle findings
on plain film radiographs to modern high-resolution sinus CT and
MR, which has allowed us to visualize the pathology within the
sinuses directly, as well as depict the normal anatomy.
Functional endoscopic sinus surgery (FESS) has driven the
requirements of sinus imaging in the realm of benign sinus disease.
The endoscopic sinus surgeons must have an accurate depiction of
the anatomy, normal and abnormal, to perform sinus surgery to
maximal effectiveness and safety. Direct coronal CT, or
high-quality reformatted coronal CT images, in combination with
endoscopy, remains the most effective method of diagnosing sinus
disease requiring surgery.
I believe it is crucial that radiology departments that perform
sinus imaging provide studies that answer the appropriate clinical
questions for the sinonasal endoscopist, and the performance of a
high-quality coronal sinus screening CT (SSCT) is of paramount
importance in the patient population with chronic sinus disease.
This overview of paranasal sinus pathology will discuss chronic
sinus disease, detail techniques to obtain very high-resolution
images of the sinuses, and outline the patient preparation that is
important in obtaining the greatest information from these scans. I
will also cover the contribution of MRI in the patient with benign
or inflammatory sinus disease and will conclude with a discussion
of imaging in malignant sinus pathology.
Chronic sinus disease
Chronic sinus inflammatory disease is a large public health
problem in the United States. Over-the-counter sinus preparations
are a large market, many workdays are lost due to chronic sinus
disease, and there is a corresponding large expenditure of
health-care dollars. Some understanding of the function of the
normal sinonasal mucociliary pathways is necessary to understand
chronic sinus inflammatory disease.
The epithelium that lines the sinonasal cavity produces a
significant volume of mucous that subsequently coats the
epithelium. This epithelium is a ciliated cuboidal epithelium, and
the cilia moves in a rhythmic fashion, directing the mucous
"blanket" toward the native ostia of the sinuses, and then
posterior toward the nasopharynx. Most of this mucous is swallowed.
This system has several points of possible derangement in function.
The mucous can be abnormal (too small in volume, too thick, etc.),
the cilia may be absent or abnormal in function, and the ostia of
the sinuses may be abnormal through development or narrowed by
previous infection or trauma, etc.
There are larger patterns of sinus drainage to consider. The
sinuses tend to drain as two major groups through an amalgam of
drainage pathways. The anterior group of sinuses include the
frontal, anterior, and middle ethmoids, and maxillary sinuses.
These sinuses drain toward the middle meatus (the airspace lateral
and superior to the middle turbinate). The final common pathway of
the anterior sinus drainage is referred to as the anterior
ostiomeatal complex, and consists of the frontal sinus ostium and
frontal recess, maxillary sinus ostium, infundibulum, and middle
meatus. The posterior group of sinuses include the posterior
ethmoids and the sphenoid sinus. These sinuses all drain toward the
superior meatus (the airspace lateral and superior to the superior
turbinate). The final common pathway of the posterior sinus
drainage is the posterior ostiomeatal complex, which consists of
the sphenoid ostium, sphenoethmoidal recess, and superior
The effect of mucociliary drainage in normal patients is to
drive the mucous blanket toward the native ostia of the sinuses.
This happens regardless of the presence of other surgical ostia,
and explains the rationale behind functional endoscopic surgery.
The functional component of the name refers to the placement of
surgical ostia at the site of the native ostia, thereby
facilitating drainage through an "enhanced" normal drainage
Screening sinus CT (SSCT) has become widely accepted as a
necessary part of the preoperative evaluation of patients who are
to undergo FESS.
Our technique for SSCT is a minor modification of the original
technique described by Zinreich,
which has gained wide acceptance from our referral otolaryngology
Typically, the decision to perform FESS is made prior to an
imaging examination, based on an appropriate clinical history of
chronic sinusitis, recurrent acute sinusitis, sinonasal polyposis
(figure 1), etc., although utilization of this surgical technique
in acute sinusitis has gained much importance.
With this in mind, the goal of the imaging examination is to
provide superior anatomic detail to the surgeon.
The performance of the exam is dependent upon an appropriate
premedication regimen to treat reversible mucosal abnormalities and
acute infections. Imaging an acutely ill patient will rarely
provide good anatomic landmarks, as the demineralization of
cartilage or bone adjacent to an active inflammatory process and
extensive mucosal abnormalities distort the anatomy that will be
encountered following the treatment of the acute infection and the
shrinkage of acutely inflamed mucosa. The importance of patient
preparation in this group has been discussed previously.
At our institution, we continue to use maximal medical therapy
to address acute infections, shrink inflamed mucosal membranes, and
reduce hyperplastic mucosa. Courses of antibiotics, nasal steroids,
oral and nasal decongestants and antihistamines, and nasal saline
washes are prescribed by the referring service. Following 2 to 3
weeks of this medical "tune-up," the patient is scheduled for SSCT.
It is appropriate to question the patient prior to the exam,
specifically about active infections or even symptoms of the common
cold, which often give rise to
transient, though significant, sinus abnormalities.
On entering the CT area, the patient is asked to clear his/her
nose and another dose of a nasal decongestant is administered.
After a few minutes, the patient is asked to clear the nose again,
and is positioned on the CT couch. In all patients who can tolerate
the position, we have used the prone coronal position. The supine,
or "hanging-head" coronal position may be used, but if free fluid
is present in the maxillary sinuses, it will tend to move toward
the maxillary sinus ostia and obliterate it. With a spiral CT, or
multidetector spiral CT, these scans can be performed in just a few
minutes. If the patient is simply unable to tolerate any form of
coronal posturing, we use very thin-section axial images (1.5 mm or
thinner) and generate coronal reformatted images on a workstation
through the nasal cavity. These images are adequate but generally
inferior to direct coronal acquisitions. This technique is also
used to generate coronal images in patients undergoing frameless
stereotaxic sinus surgery with the VTI device (Visualization
Technology Inc., Wilmington, MA).
Following a lateral scout radiograph, the images are acquired as
close to perpendicular to the hard palate as achievable. We perform
1.5-mm sections at 3-mm intervals through the entirety of the
sinuses. The high spatial resolution of the thin sections minimizes
partial volume effects. The interslice gap is not significant in
routine clinical imaging. This technique provides excellent
depiction of the regional anatomy, but variants of this technique
Our technique provides adequate information for patients with
disease either in the anterior or posterior ostiomeatal unit. Some
authors advocate the performance of limited axial scans in patients
with disease of the posterior ostiomeatal complex.
Coronal images depict the anatomy at the orbital apex well,
and the reflection of an asymmetric sphenoid septum onto the
carotid can be evaluated. If the referring physician wishes to view
axial images of the sphenoid sinus in this patient subset, these
images can be performed in addition to the coronally acquired
images. However, with a good-quality coronal spiral CT data set,
the technologists can reprocess the data without an interslice gap,
or ideally with some overlap of reconstruction intervals, and
perform reformatted axial images on a workstation. These are
diagnostic-quality images, obtained without additional radiation,
and are certainly adequate for the purpose of depicting the bony
septum and the location of vascular structures. No intravenous
contrast is needed. The images are obtained with as small a
field-of-view as is appropriate for each patient.
The scan technique is quite low (100 mAs), which results in low
patient exposure. Lower exposures may be acceptable, and should be
evaluated by individual sites. The anatomy depicted on these scans
has high inherent contrast and the low technique is quite
The data is processed with a high-resolution algorithm that
sharpens edge definition. Certainly, wide variations in the
performance of sinus CT exists, but I believe our established
technique is performed easily, acquires high-quality sinus images,
is consistent across our patient base, and demonstrates our concern
with reducing radiation exposure. Few doubt the necessity for
thin-section imaging, and 3 mm or less is believed to be the
We have adopted 1.5 mm, as images between 1 and 2 mm thick seem to
be less affected by partial volume effects. We print the images at
an extended level and window setting (-200/2000 HU), which provides
depiction of the often delicate ethmoid septae, and emphasizes the
air-tissue interfaces. Others have described the importance of
proper windowing to maximize the depicted information.
We do not routinely print additional images at other level and
window settings, although some report this to be necessary.
In fact, the techniques we choose for performance of these
examinations practically guarantees that, unless the data is
reprocessed or additional images are acquired, we obtain poor
soft-tissue contrast, and consequently generate low-quality images
of the brain, or orbital contents.
Again, this technique is an imaging technique specifically for
the patient with chronic sinus disease. It is not an appropriate
imaging choice for patients with headaches, a "runny nose," or
other nonspecific complaints. The images are adequate for
evaluation of various densities within the sinus contents, which
can be indicative of fungal sinus disease or concretions within the
sinuses. If there is concern for orbital pathology, intracranial
pathology, or other extrasinus complications, the SSCT alone is not
an appropriate choice of imaging test. These patients will require
axial images, intravenous contrast, or likely MRI. Very close
attention to detail is critical in assuring the high quality of the
Bone erosion, abnormalities of the fovea ethmoidalis, cribriform
plate, or lamina papyracea, or frank bony destruction are not the
imaging picture of sinus inflammatory disease and should be "red
flags" for the imaging physician. These findings warrant additional
imaging (figure 2), typically with the administration of
Certain clinical warning signs, such as facial numbness, epistaxis,
or orbital or intracranial signs and symptoms are also "red flags,"
and should increase our vigilance.
Acute sinus inflammatory disease
The typical patient seen with acute sinus inflammatory disease
needs no imaging. The clinical diagnosis is made, the patient is
treated appropriately, and clinical follow-up dictates the
necessity for additional management. In problematic cases, some
clinicians rely on plain film radiographs of the sinuses. We have
tried to minimize the reliance on these studies, and move to a
limited CT study in these patients. Plain film radiographs are at
best difficult to interpret, and at worst may confuse the clinical
In most active clinical practices, however, the number of patients
requiring imaging should be low. The patient with orbital or CNS
signs or symptoms is the most important group to consider in the
setting of acute inflammatory or infectious disease. In this group,
some consideration of the eventual therapeutic approach is
important, but the literature seems to be clear that MRI is the
most sensitive evaluation we can offer. If CT is readily available,
a study including axial and coronal evaluation of the orbit and
contiguous intracranial structures is necessary, and the exam
should be performed with intravenous contrast. MRI should also
include contrast media. The inclusion of MR angiography or MR
venography can be determined by the extent of disease visualized,
or clinical concerns of venous or arterial involvement. Orbital
sequelae of ethmoid or frontal sinus inflammatory disease can
include involvement by mucoceles (figure 3), subperiosteal
abscesses, orbital phlegmon, venous thromboses, or frank orbital
abscesses. Intracranial inflammatory sequelae include involvement
by mucoceles, subdural or epidural abscesses, meningitis,
parenchymal abscesses, and dural sinus thromboses (figure 4). The
benefit of MRI in this setting is its clear superiority in
depicting soft tissue. The benefit of CT is its ability to be used
as a surgical roadmap when a nasal endoscopic approach is to be
used. The endoscopists have moved outside the realm of chronic
sinus inflammatory disease, and now routinely approach acute
inflammatory disease and its sequelae with primary endoscopy.
The diagnosis of sinus neoplasia remains a clinical problem for
most physicians treating large numbers of patients with sinus
complaints. Unfortunately, the signs and symptoms of sinus
neoplasia are largely those of sinus inflammatory disease
(particularly early in the disease course), and delay in diagnosis
is common. This means that the radiologist must keep in mind that
any patient imaged for "chronic sinusitis" may instead harbor a
neoplasm, and the image interpretation may be key for early
diagnosis in the involved patient. There are "red flags" that
accompany sinus neoplasia that the radiologist should keep in mind
when evaluating sinus CT. These are findings that do not typically
accompany benign chronic sinus inflammatory disease, and may point
to a tumor. When confronted with these signs, the radiologist may
choose to perform the study in a different fashion, administer
iodinated contrast, or recommend additional evaluation with MRI.
The "red flags" include bony erosion, discernable soft-tissue
masses, significant unilateral or focal disease, or the presence of
significant bony remodelling. Clinical "red flags" that should also
raise suspicions of neoplasm include significant epistaxis, cranial
nerve or orbital findings, or facial deformity.
Sinus neoplasia is fortunately an uncommon tumor, representing
< 4% of neoplasms of the head and neck.
CT and MRI play complementary roles in the evaluation of sinus
neoplasia. Clearly, MRI is an important examination in the
evaluation of these patients, and few surgeons would contemplate a
surgical approach without it. CT continues to play a key role in
the evaluation of the bony changes accompanying the tumor and in
helping to determine the surgical approach to the tumor. CT studies
of these patients should include axial and coronal images with
iodinated contrast. We typically screen the suprahyoid neck for
nodal disease, but do not routinely examine the entire neck, unless
there is clinically palpable cervical disease. If nodal disease is
determined to be present in the suprahyoid neck, the exam is
continued to evaluate for lower cervical adenopathy. Depiction of
the bony anatomy is key, and visualization of the facial skeleton
with wide windows must be performed. MRI studies should include
both T1- and T2-weighted images of the paranasal sinuses, and
include contrast media. We routinely perform the postcontrast
images with fat suppression. The choice of axial, coronal, and
sagittal images is somewhat dependent upon local opinion, but
should typically include all planes. The inclusion of T1- and
T2-weighted images increases the specificity of the exam to
delineate tumor from contiguous sinus secretions of varying ages.
This is a particular problem with CT; there is often no clear
distinction from contiguous inflammatory fluid within the sinus and
tumor. Enhancement can be of some help, but the distinction on MR
is often very clear (figure 5).
Both MRI and CT are of poor diagnostic accuracy in determining
the cell type of tumor.
The role of the radiologist is to indicate where tumor is and where
it is not. A knowledge of the typical pattern of spread of these
diseases is important, but beyond the scope of this article. Many
of these tumors have rather specific patterns of spread, such as
the perineural tumor spread of adenoid cystic carcinoma. The
evaluation of the neural structures that could potentially be
involved becomes of critical value. Aggressive changes, including
bone destruction, are common; but interestingly, many of the tumors
also demonstrate chronic bone changes, with sclerosis and
occasional smooth remodelling of the bone. The histopathology will
be best determined by the pathologist at the time of biopsy or
resection. With a skilled Otolaryngology Department, the lesions
will most commonly come to the imaging area with a diagnosis
already established. Flexible nasal endoscopy and biopsy has
already been performed. Benign neoplasms of the nasal cavity are
seen occasionally, including the juvenile nasopharyngeal
angiofibroma of adolescent males (figure 6), and polyps and
papillomas of the nasal cavity in older patients. The lesion seen
most commonly is a squamous cell carcinoma of the sinus mucosa.
ma, and melanoma are also seen, and the myriad of minor salivary
gland neoplasia occur with some frequency. Nasal cavity lesions and
paranasal sinus neoplasms can also include many unusual tumors,
including the ectodermal derivative tumors of the superior nasal
cavity and ethmoid cells, derived from olfactory epithelium. Many
of these lesions fall into the category of "little round blue
cells," and the diagnosis by light microscopy is difficult; most
require immunohistochemistry for diagnosis.
The imaging of sinus pathology, both benign and malignant, has
undergone radical changes from the era of plain film radiography.
The current application of high-resolution CT and MRI to this
anatomic region has benefited patients, reduced unnecessary
surgery, and allowed the introduction of a whole new surgical
technique into common use.