plays a crucial role in the diagnosis and management of nasal polypi.
The following are some of the important contributions imaging is
supposed to make:
It clinches the diagnosis
It helps in evaluation of progression of disease
Helps in surgical planning
Helps in monitoring for recurrence
scan is the primary imaging modality used to evaluate patients with
chronic sinusitis with nasal polyposis. MRI has only a limited role to
play and is used only sparingly. Imaging may be really vital and could
even replace diagnostic nasal endoscopy in patients whose nasal
cavities are completely filled with polypi and is virtually impossible
to perform diagnostic evaluation using a nasal endoscope. This scenario
is tailor made for imaging.
CT appearance of nasal polypi:
appear as rounded bodies of soft tissue arising from the mucosal
surfaces of nose and paranasal sinuses. They can be clearly
differentiated from the surrounding inflammed mucosal lining and nasal
secretion as they are more radio dense and hence appear brighter.
Rarely a pedicle attaching the polypoidal mass to the nasal mucosal
lining can be seen clearly in the CT scan (pedicle sign). If present it
is virtually diagnostic of nasal polypi.
important point that should be borne in mind while evaluating CT images
from a patient with nasal polypi is that they never cause bone erosion.
If soft tissue mass arising from the nasal mucosa is associated with
bone erosion then it is a definite pointer towards the diagnosis of
malignancy. Pressure effects of nasal polyp can be evidently seen in
imaging. These effects include local bone remodelling causing a
scalloping effect. This scalloping effect should not be confused with
that of the scalloping of margins produced by the mucocele since it is
always associated with enlargement of the sinus cavity. Rarely this
bone remodelling may occasionally cause thinning of the bony septa of
the ethmoidal sinus. This thinning could be so extreme that it could go
even below that of the resolution of the CT scan. This creates a
picture of bone erosion which is not a true one.
Appearance of nasal polyp when contrast CT is taken:
polypi do not show enhancement on injection of contrast media. The
mucosa surrounding the nasal polyi may show enhancement causing an
impression of rim enhancement around the nasal polypi.
Types of nasal polyp:
polypi – arising from ethmoidal sinus and are multiple. They can be
visualised in the CT scan of paranasal sinuses as multiple polypoid
lesions. Polypi arising close to the cribriform plate area can cause
arising from the maxillary sinus – is usually solitary. It exits the
antrum via the natural / accessory ostium. This causes an enlargement
of ostia. Radiologically it appears like a dumbbell because of the
constriction present in the midline (ostial exit point). In these
patients the medial wall of the maxillary sinus bows into the nasal
cavity. This can be clearly visualised in the CT scan images.
Obstruction caused by this polyp to the drainage channels of ethmoidal
and frontal sinuses (middle meatus) can cause opacification of those
sinuses also there by making it difficult to identify the exact origin
of the nasal polyp. In this scenario the bone remodelling that takes
place in the medial wall of maxillary sinus could be the clincher. If
these polyp passes posteriorly to exit via the choana it could be
clearly visualized in the axial cuts taken at the choanal level.
disease may coexist with nasal polypi. If present they could be
visualized as hyperdense areas between the nasal polypi shadows.
CT differences between acute sinusitis & nasal polypi:
sinusitis causes a near uniform opacification of the paranasal sinuses
whereas nasal polypi inaddition to the opacification show multiple
retention cyst can be safely eliminated if the polypo shows a pedicle
radiologically. If there is associated bone remodelling then in all
probability it could be nasal polyp rather than mucous retention cyst.
In case of diagnostic dilemma MRI will clinch the diagnosis.
cystic fibrosis in addition to the radio densities seen in the CT scan
images there is also associated thickening of the maxillary sinus walls
due to osteoneogenesis.