In this essay,
we will discuss the CT and MRI findings in cases of esthesioneuroblastoma and their complementary role in staging of the disease using modified TNM staging.
Computed tomography:
CT protocol should include thin axial slices (1-5 mm thick) with IV contrast administration and reformation in both coronal and sagittal planes.3
ENB appears as homogeneous density soft tissue mass in the nasal vault,
which is iso-or slightly hyperdense to the surrounding muscles.
The mass shows moderate and uniform post contrast enhancement.3,4,5 Fig. 1
They commonly extend to ipsilateral ethmoid and maxillary sinuses and only rarely involve the sphenoid sinuses.
When large,
they can extend to involve both sides of nasal cavity and the paranasal sinuses.3,4,5 Fig. 2
Intralesional calcification and presence of cysts along the intracranial margins in case of intracranial extension are specific findings in cases of ENB.3,4,5
Bone remodeling and bony erosion is not an uncommon finding in ENB and CT is the modality of choice to detect these changes.4,5 Fig. 3
Thus,
CT is necessary to detect the involvement of osseous structures,
intralesional calcifications or regional and distant metastasis.
MRI :
The MRI appearance is often that of a large,
soft tissue,
dumbbell shaped mass centered within the superior nasal cavity and extending intracranially.3,4,5
The tumor is generally hypointense to gray matter on T1-weighted images and iso- to hyperintense on proton density and T2-weighted images.3,4 Fig. 4
Contrast enhancement is usually avid and homogeneous except for occasional areas of necrosis and hemorrhage Fig. 5 .
Cystic areas within the lesion can be seen in some cases.
Fig. 6
MRI can accurately delineate the intraorbital and intracerebral extension and determine the meningeal,
extradural or perineural spread.3,4,5
Obstruction of sinus draining ostia results in an accumulation of nasal secretions and can be difficult to differentiate from tumor tissue on computed tomography.
These post-obstructive secretions can be easily differentiated on MRI,
showing markedly hyperintense signal on T2WI seen separately from the less hyperintense or isointense tumor in the same images.
Fig. 7
Thus,
MRI is more specific in assessing soft tissue extent,
intracranial/orbital/skull base invasion and differentiating post operative secretions from recurrences.
STAGING
Accurate staging of the disease at the initial presentation is essential,
as it is highly predictive of survival.
There is no universally accepted staging system,
though several have been proposed.3,4
Kadish et al.
developed the first and most widely used system to classify the anatomical extent of ENB.3,4
The Kadish staging system used three categories,
group A,
B,
and C: 3,4,5
Group A: tumor confined to the nasal cavity.
Group B: tumor extends into the paranasal sinuses.
Group C,
tumor extends beyond the nasal cavity and paranasal sinuses including involvement of the cribriform plate,
skull base,
orbit,
or intracranial cavity.
Modified Kadish staging was later introduced which included a fourth stagefor patients with nodal or distant metastases.3,4
This system has been criticized because it requires surgical staging,
does not incorporate metastatic spread,
and lacks prognostic value.
In 1992,
Dulguerov and Calceterra proposed another classification based on the tumor,
node,
metastasis (TNM) system,
thus allowing staging of patients treated with chemoradiation or otherwise deemed inoperable.3,4,5
Fig. 8: TNM staging of esthesioneuroblastoma as proposed by Dulguerov.
Imaging of the neck should also be added to the imaging protocol as patients with ENB present with neck metastases at presentation in 5% of cases,
while 23% patients may eventually develop cervical lymph node metastasis.
Spine is the most common site for distant bony metastasis seen in 86% patients and thus a bone scan should be included in the diagnostic workup for staging.
CT and MRI play a complimentary role for TNM staging and detection of recurrent tumour.
While,
CT provides best information about invasion into bony structures such as the cribriform plate,
MR imaging is more specific in delineating the soft-tissue invasion,
differentiating tumor from postobstructive inflammatory sinus disease,
and detecting recurrent or metastatic disease at an early stage.3,4,5
Since around 57% of tumors are locally recurrent,
the protocol for follow-up should consist of an contrast-enhanced MRI 2 to 4 months after completion of all therapy,
and then repeated every 4 to 6 months for 5 years and then annually for the patient's lifetime.5 In addition,
an annual chest radiograph should be performed to exclude the presence of metastases.5
DIFFERENTIAL DIAGNOSIS:
Common differential diagnosis includes:
Nasopharngeal carcinoma6: Most common primary malignancy of nasopharynx.
Common in patients aged 40-60 years.
They originate in the lateral pharyngeal recess,
also known as the fossa of Rosenmuller and show preference for superior spread to the skull base causing skull base erosion,
rather than inferior spread to the oropharynx.
They show marked local invasion and heterogeneous enhancement on imaging.
Fig. 9
Fungal sinusitis7: It can be acute or chronic and invasive or non invasive.
Acute invasive fungal sinusitis may appear as hypoattenuating mucosal thickening with soft tissue opacification and expansion of the sinuses plain CT.
Surrounding bony erosion with minimal or no post contrast enhancement is seen.
MRI can detect intraorbital and intracranial extension accurately by identifying inflammatory changes in the orbital fat and extraocular muscles.
Mucocele8: It represents complete opacification of paranasal sinuses by mucus,
often associated with bony expansion due to obstruction of the nasal sinus drainage.
On CT it is seen as an isodense/mildly hyperdense sinus opacity with expanded and thinned out margins.
Minimal peripheral post contrast enhancement can be seen.
Fig. 10 On MRI initially,
the contents will be predominantly aqueous,
so the corresponding image will be hypointense on T1-weighted,
and hyperintense on T2-weighted sequences.
Over time,
the protein contents may increase; resulting in hyperintense images both on T1- and T2- weighted sequences.
Olfactory groove meningioma: Rare type of meningioma which arises in midline in the anterior cranial fossa overlying the cribriform plate,
frontosphenoid suture and planum sphenoidale.
Most patients are women in their 5th and 6th decades of life.
It appears as an extra-axial mass along the planum sphenoidale/olfactory groove within the midline with an intermediate signal intensity on T1-weighted sequences and slightly high signal intensity on T2-weighted sequences.
Blooming on gradient images may be seen if calcified.
Homogeneous enhancement with an enhancing dural tail is the differentiating feature.
It can cause hyperostosis of the skull base or invade the sinuses,
and rarely,
the orbits.