Transcript Hypo and anosmia: causes and imaging aspects

Hypo and
anosmia:
causes and
imaging
aspects
H. ZAGHOUANI BEN ALAYA, Z.
ACHOUR, W. BEN AFIA, W. KARMANI,
S. MAJDOUB, H. AMARA, D. BAKIR,
CH. KRAIEM
HN26
Purpose:
The aim of this work is to highlight imaging
aspects of the common causes of smelling
loss or weakness especially on MRI.
Patients and method
we conducted a retrospective review of 7 patients
who had come with a chief complaint of anosmia.
All patients had undergone an imaging evaluation by
either MRI or CT.
the causes were:
 nasal polyposis (3 cases),
 head injuries (2 cases),
 kallmann syndrome (2 cases),
 and olfactory meningioma (1 case)
RESULTS:
The etiology of olfactory loss is varied.
NASAL POLYPOSIS:
Axial and corona CT images:
polypoid masses associated with
partial pansinus opacification and
infundibular widening.
OLFACTORY MENINGIOMA:
a
a
b
c
d
A well circumscribed extra
axial dura based lobulated
mass at the floor of anterior
cranial fossa in the mid line
overlying cribriform ethmoid.
Lesion is soft tissue signal
intensity slightly hyperintense
to cortical grey matter, no
cystic component. (a, b and c)
T2 hyperintense perilesional
odema in adjacent brain
parenchyma.
Homogenous enhancement on
post contrast T1. (d)
kALLMANN SYNDROME:
coronal T2 images through the frontal lobes demonstrate abnormal
anatomy with absence of the olfactory bulbs and sulcus.
The gyrus rectus and medial orbital gyrus are normal.
Coronal T2-weighted MR image through the anterior fossa.
olfactory bulbs are absent and the left olfactory sulcus is hypoplastic.
DISCUSSION:
Smell a disorders are common in the general population.
Although these disorders can have a substantial impact on
quality of life and may represent significant underlying disease
Based on the site of the pathology, clinical olfactory deficits are
classified as one of three types: transport, sensory, or neural.
Imaging has an important role in diagnosis.
Simplified diagram of cortical regions
thought to be involved in the processing of
olfactory information as it passes from the
olfactory epithelium to the brain.
SINO NASAL POLYPOSYS:
nasal polyposis does not appear to be a single disease
entity but may correspond to a uniform reaction of the
nasal mucosa to a variety of stimuli.
Since polyps result from fluid accumulation and have an
hypocellular nature, they demonstrate a fluid density on
CT.
Symptomatic polyposis occurs in 1% of the population
Histogically, they differ from mucoperiosteal thickening
of chronic sinusitis in that they have fewermucus
secreting glands and a disordered vascular bed but these
differences cannot be revealed by CT imaging.
CT scan is the preferred imaging technique for the
diagnosis of polyps and the evaluation of the extent
of polyposis.
In clinical practice, sinonasal polyposis diagnosis is
usually assessed by endoscopy but CT scan is
frequently performed to help evaluate the disease.
IMAGING:
The major CT features are polypoid masses
associated with partial or complete pansinus
opacification and infundibular widening.
Less frequent CT characteristics include polyps
within the individual paranasal sinuses, attenuation
of the bony ethmoid trabeculae
Truncation of the bony middle turbinate is also a
feature of polyposis which may be present iny60% of
patients.
When polyposis is more severe, bony changes take
on a destructive appearance.
CT is important to confidently diagnose sinonasal
polyposis, to appreciate its extent and severity, and to
properly evaluate deeper pathology which is not
visualized by endoscopy.
In this respect, coronal CT should be performed
when endoscopy fails to explain symptoms reported
by the patients. Isolated, unilateral polyposis should
be regarded with suspicion and also requires CT
because it suggests malignancy. When medical
therapy has failed or when steroid treatment is
contraindicated, surgery can be elected and preoperative assessment includes CT examination.
OLFACTORY MENINGIOMA:
By virtue of their subfrontal location, GM may
become very large prior to producing symptoms.
Personality changes, such as apathy and akinesia, can
be common when the tumors grow to large sizes .
Onset of these symptoms is gradual, and they may
not be observed early in their course.
Other common symptoms include headache and
visual deficits.
Interestingly, anosmia is noted in hindsight by a
significant number of patients, although it is not a
common primary complaint.
IMAGING: CT:
Computerized tomography scanning is particularly
useful for defining the osseous anatomy, including
areas of hyperostosis or erosion that may assist in the
diagnosis or planning of a surgical approach to these
lesions.
Meningiomas typically appear slightly hyperdense
relative to the brain parenchyma on non contrast CT
scans and enhance homogeneously and brightly after
administration of contrast.
Paranasal sinus extension through the floor of the
anterior cranial fossa is well demonstrated on CT
scans, particularly on coronal views.
MRI:
Both MR imaging and MR angiography will define
the relationship of the tumor to the optic nerves and
chiasm as well as the anterior cerebral arteries and
communicating complex.
Meningiomas commonly appear isointense to gray
matter on T1-weighted sequences and iso- or
hyperintense on T2-weighted sequences.
Dense enhancement after administration of
Gadolinium is also seen.
Posttraumatic olfactory dysfunction:
The prevalence of posttraumatic anosmia ranges from
24% to 30% among patients who have sustained severe
TBI (traumatic brain injury).
 In overall, about 5% of all patients admitted to hospital
with a TBI is known to have anosmia.
 The precise cause and mechanism is not clearly
uncovered yet.
 However, shearing injuries at the cribriform plate that
lacerate the primary olfactory nerves extending from
the nasal cavity to the olfactory bulb seem to be the
most common mechanism involved in posttraumatic
smell loss.

On MRI in patients with posttraumatic
olfactory dysfunction, the injury sites reported were:

olfactory bulb and tract (88%),

subfrontal region (60%),

temporal lobes (32%).

Decrease in volume and size of the olfactory bulb was
also reported.
CONCLUSION:
Loss or weakness of smell is a common but hidden
problem.
CT and MRI of the brain and sinus can be useful to
establish the etiology.