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Page 4 of 10 Sell et al. Mini-invasive Surg 2024;8:3 https://dx.doi.org/10.20517/2574-1225.2023.105

MRI
MRI is thought to be the gold standard for assessing the recurrence of sinonasal malignancies. Generally, a
baseline MRI of the brain and sinonasal cavity will be performed at 3-4 months following primary
treatment [23-25] . Compared to other imaging modalities, MRI has been shown to have a higher PPV (46% to
84%) in monitoring for recurrence of sinonasal malignancies [15,26] . T2-weighted images are often employed
[21]
in signal discrimination, while T1-weighted images are frequently used with postcontrast comparison .
Although MRI is a powerful and informative imaging modality, the interpretation of MRI images can be
variable; individual providers and various institutions may have different criteria for evaluating findings
suspicious of recurrence of sinonasal malignancy on MRI, leading to considerable discrepancies in findings
considered suspicious for recurrence.

New techniques for MRI have attempted to help refine and standardize the detection of recurrence of
sinonasal malignancy. Dynamic postcontrast-enhanced MRI has proven to be useful in distinguishing post-
radiation fibrosis from tumor recurrence, which can demonstrate similar enhancement on standard
MRI [22,27] . Diffusion-weighted imaging (DWI) MRI may also have utility in differentiating posttreatment
inflammation from tumor recurrence. As a result of the complex bone-air-fat interface, DWI has high-
susceptibility artifacts that can reveal variations on enhancement for particular sinonasal malignancy
[21]
subtypes, particularly intestinal-type adenocarcinoma . Because the diffusion of water molecules is limited
in solid tumors with hypercellularity, higher apparent diffusion coefficient (ADC) values can be indicative
[28]
of hypocellular tissue with apoptosis or necrosis . As a result, DWI has been investigated as a tool that
could allow for earlier surveillance imaging of patients with head and neck cancers [29,30] . With additional
research, innovative techniques to assess for recurrence that can be distinguished from posttreatment
inflammation and fibrosis will continue to emerge, further improving MRI, the gold standard imaging
modality for surveillance of sinonasal malignancies.

COMPUTED TOMOGRAPHY
Computed tomography (CT) has largely been overtaken by MRI as the primary imaging modality for
monitoring the recurrence of sinonasal malignancies; however, a few factors could warrant the use of CT for
surveillance imaging. CT can have higher utility in assessing for acute intracranial complications in the
[21]
post-operative period . Because of its high spatial resolution, CT can be particularly valuable in assessing
the resorption of thin bony structures and could play a role in surveillance imaging for tumor subtypes with
a particular predilection for bony involvement. CT imaging has been suggested to be equivalent to MRI for
a few subtypes of sinonasal malignancy, namely SNUCs and extranodal Nk/T-cell lymphoma. SNUCs are
characteristically noncalcified on CT and MRI, making recurrence difficult to evaluate on either
modality . NUT carcinoma has distinct findings on CT, including hypoattenuation, heterogeneous
[31]
[32]
enhancement, and infiltrative mass with not well-defined margins . NUT carcinoma also exhibits necrosis
and calcification with invasion into nearby structures, often in central airways and vascular structures,
which can be assessed on CT and MRI . In younger patients, surgeons should consider the risks of
[33]
secondary malignancy from repeated CT radiation when choosing optimal imaging modality . Overall, CT
[34]
is most useful when combined with FDG-PET imaging.
18
PET/CT
The NCCN guidelines recommend FDG-PET/CT for surveillance following completion of primary
18
[12]
treatment for the head and neck cancer . Multiple studies have demonstrated that PET/CT can identify
approximately 95% of recurrences that are asymptomatic in the first two years following completion of
[36]
primary treatment [12,22,35] and has a higher sensitivity when compared to CT/MRI alone . PET/CT also has
the powerful advantage of the ability to detect distant metastases as unexpected areas of