MRI Paranasal Sinuses — Generic Standard Protocol

MRIninja Knowledge Base | Master / General Protocol Page Related pages: MRI Cranial Nerves Generic Standard Protocol · MRI Soft Tissues Neck Generic Standard Protocol · MRI Orbit Generic Standard Protocol Version 1.0 — May 2026

1. Executive Summary

MRI of the paranasal sinuses occupies a specific and complementary role to CT in sinonasal imaging. High-resolution CT (HRCT) of the paranasal sinuses is the primary modality for inflammatory sinonasal disease, surgical planning (functional endoscopic sinus surgery — FESS), and bony anatomy assessment. MRI is the primary modality for soft tissue characterisation, intracranial and orbital complication assessment, and tumour staging. The fundamental principle governing the use of MRI for the paranasal sinuses is the same as for all sinonasal imaging: CT and MRI answer different clinical questions and are complementary, not interchangeable.

The paranasal sinuses present a technically challenging MRI environment. The complex air-bone-mucosa-soft tissue interfaces of the nasal cavity, ethmoid cells, maxillary sinuses, sphenoid sinus, and frontal sinuses create significant B0 inhomogeneity, susceptibility artefacts, and chemical shift effects. The proximity of dental metalwork (a near-universal feature in adults) to the maxillary sinuses and the hard palate produces susceptibility artefacts that can obscure the inferior maxillary sinus and the nasal floor. The air cells themselves produce EPI distortion comparable to the middle ear — making standard single-shot EPI-DWI unreliable for small sinonasal lesions.

Despite these challenges, MRI provides unique diagnostic information that CT cannot: soft tissue characterisation of sinus content (retained secretions vs soft tissue mass vs fungal mucin); tumour characterisation and staging (T3/T4 invasion of orbital fat, dura, brain, pterygoid plates, masticator space); perineural spread along CN V2 and V3; and differentiation of tumour from obstructed secretions (a critical staging distinction that CT cannot make).

1.1 Core Strengths

Soft tissue characterisation of sinus content: the most important and distinctive MRI contribution. CT shows opacification of a sinus but cannot reliably distinguish: simple retained mucus (T2-very bright, no enhancement) from soft tissue tumour (T2-intermediate, enhances) from allergic/fungal mucin (T2-dark, characteristic hypointense centre). MRI makes this distinction reliably — a distinction that directly affects staging and surgical planning.

Tumour extent and staging: sinonasal tumours (squamous cell carcinoma, adenocarcinoma, olfactory neuroblastoma, sinonasal undifferentiated carcinoma) require MRI for T3/T4 staging. CT detects bony erosion but underestimates soft tissue extension. MRI directly visualises:

• Orbital fat invasion (T2-bright fat replaced by intermediate tumour signal)
• Dural invasion or intracranial extension (post-contrast T1: dural enhancement, brain parenchymal invasion)
• Pterygoid plate erosion and pterygomaxillary fissure invasion
• Perineural spread along the infraorbital nerve (CN V2 branch) or palatine nerves

Intracranial and orbital complications of sinusitis: orbital cellulitis, subperiosteal abscess, epidural abscess, subdural empyema, and cerebral abscess are primary MRI indications when acute sinusitis presents with orbital or neurological signs. Post-contrast T1 and DWI are the key sequences.

Inverted papilloma characterisation: the convoluted cerebriform pattern of inverted papilloma on T2-weighted MRI is pathognomonic (sensitivity ~80–90% in published series [1]), providing pre-surgical tissue characterisation that CT cannot. This pattern directly influences surgical approach planning.

Post-treatment assessment: after sinus surgery or chemoradiation for sinonasal malignancy, MRI distinguishes residual/recurrent tumour from post-treatment fibrosis and mucous retention — a distinction CT cannot make reliably.

1.2 Intrinsic Limitations of the Generic Protocol

CT remains the primary modality for inflammatory sinonasal disease: the generic sinonasal MRI protocol is not appropriate as a replacement for CT in the workup of chronic rhinosinusitis for FESS planning. The bony anatomy (uncinate process, lamina papyracea, cribriform plate, sphenoid face, anterior ethmoid artery position) that the surgeon needs is better defined on CT. MRI is the modality for soft tissue questions after CT has defined the bony anatomy.

Dental metalwork susceptibility: posterior dental metalwork (amalgam, metal crowns, implants) produces susceptibility artefacts extending into the posterior maxillary sinuses and hard palate. At 3T, these artefacts can be 3–5 cm in extent, obscuring the posterior maxillary sinus, the infratemporal fossa, and the pterygopalatine fossa — precisely the regions of highest oncological importance for sinonasal tumour staging. This limitation is inherent and unavoidable without substituting 1.5T imaging.

Small nasal cavity detail: the nasal turbinates, nasal septum, and osteomeatal complex detail that ENT surgeons require for FESS planning are better resolved on thin-slice CT (0.5–0.6 mm) than on MRI (even at 3 mm).

When dedicated child protocols are required: sinonasal malignancy staging and post-treatment surveillance; inverted papilloma characterisation and recurrence; angiofibroma (JNA) pre-operative embolisation planning; invasive fungal sinusitis (immunocompromised patient); orbital complication of sinusitis; intracranial complication of sinusitis; sinonasal lymphoma; olfactory neuroblastoma staging.

2. Main Clinical Indications

2.1 Standard Indications

Sinonasal mass characterisation is the leading indication for sinonasal MRI. When CT demonstrates a soft tissue mass in the nasal cavity or paranasal sinuses, MRI characterises the lesion (benign vs malignant; soft tissue vs retained secretions vs vascular lesion vs bony lesion), assesses extent, and guides biopsy planning. The generic protocol is appropriate for initial characterisation. Staging of confirmed malignancy requires a dedicated protocol.

Orbital complications of acute sinusitis represent one of the few genuinely urgent sinonasal MRI indications. Preseptal cellulitis (periorbital but not orbital) does not require MRI. Once proptosis, ophthalmoplegia, visual loss, or chemosis develops, post-septal orbital involvement (orbital cellulitis, subperiosteal abscess) must be assessed urgently. MRI with post-contrast T1 and DWI is the modality of choice — it defines the abscess, its relationship to the periorbita and orbital apex, and any intracranial extension.

Intracranial complications of sinusitis — Pott's puffy tumour (frontal bone subperiosteal abscess); epidural/subdural abscess; meningitis; cerebral abscess — require emergency MRI (brain protocol + sinonasal protocol) when clinically suspected.

Inverted papilloma pre-operative staging: the generic protocol with post-contrast T1 and T2 (with attention to the cerebriform pattern) characterises the lesion and assesses its attachment site. If the papilloma involves the frontal recess or sphenoid sinus, or if intracranial extension is suspected, the dedicated child page protocol is preferred.

Suspected sinonasal malignancy — initial assessment: when CT demonstrates an aggressive sinonasal mass with bony erosion or orbital involvement, MRI provides the initial soft tissue staging. Confirmed malignancy then proceeds to the dedicated child protocol for full staging.

Post-operative sinonasal assessment — for follow-up after FESS or sinonasal tumour surgery, MRI distinguishes recurrent tumour (enhancing soft tissue) from post-surgical change (enhancing granulation tissue initially; non-enhancing fibrous tissue later) and mucosal thickening.

Angiofibroma (JNA) in adolescent males: juvenile nasopharyngeal angiofibroma is a highly vascular benign tumour arising in the pterygopalatine fossa. MRI with post-contrast T1 and TOF or CE-MRA characterises the hypervascular tumour, defines its extent, and provides vascular anatomy for pre-surgical embolisation planning. The generic protocol is the initial assessment; dedicated MRA/MRI for embolisation planning is the child protocol.

2.2 Urgent Red Flags Requiring Expedited or Emergency Imaging

3. Preparation Reference

Universal MRI safety screening belongs to the general MRI preparation page and is not repeated here.

3.1 Anatomy-Specific Preparation Items

Dental metalwork — the dominant preparatory concern: the position and extent of metalwork in the upper dental arch directly determines image quality in the maxillary sinus and pterygopalatine fossa regions. Before the examination:

• Review any available prior CT or plain films for metalwork type and location
• Ask the patient specifically about metal crowns, implants, bridges, and orthodontic appliances in the upper jaw
• Removable upper dentures must be removed before the examination
• Fixed metalwork (crowns, implants) cannot be removed but the patient should be informed that image quality may be affected in the posterior maxillary sinus region

At 3T, posterior upper dental metalwork produces artefacts extending 3–5 cm — this is a clinical limitation that must be mentioned in the report if it affects the diagnostic region.

Prior sinus surgery: the post-operative sinonasal anatomy is complex. Partial or complete resection of turbinates, removal of the uncinate process, maxillary antrostomy, and sphenoidotomy all alter the expected anatomy and the expected MRI appearance. Review the surgical history to understand which structures have been removed. Post-FESS fat grafts or packing materials (Gelfoam, Merocel) may produce specific MRI signal characteristics that must not be misidentified as tumour recurrence.

Coil selection: a standard 16–32 channel head coil provides adequate SNR for sinonasal MRI. For targeted skull base or pterygopalatine fossa assessment requiring maximum resolution, the head coil with isocentre at the face (rather than the brain) provides better B0 homogeneity in the region of interest.

3.2 Patient Positioning on the MRI System

Position: supine, head-first. Standard head coil.

Isocentre: for sinonasal MRI, the isocentre should be positioned at the level of the nasal bridge / mid-face, rather than at the standard brain isocentre (nasion or midface). This places the maxillary sinuses and ethmoid complex at the B0 field centre, optimising shimming and fat suppression quality for the target anatomy.

This is the primary difference from standard brain MRI positioning. If the isocentre is at the brain centre, the sinuses (10–15 cm below the brain centre) are off-isocentre, and spectral fat suppression (SPAIR) fails in the maxillary region — directly affecting the quality of the post-contrast T1.

Head alignment: no rotation; chin slightly elevated (chin-up position) aligns the hard palate perpendicular to the scanner bore axis, which facilitates axial and coronal slice planning parallel to the sinonasal anatomy.

4. Standard Protocol Design

4.1 Mandatory Core Sequences

4.2 Conditional Sequences

4.3 Rationale Summary Per Sequence

T2-weighted TSE coronal — the primary and most diagnostically informative sinonasal sequence. The coronal plane is the natural plane for sinonasal assessment: it shows all sinuses (maxillary, ethmoid, frontal) bilaterally in one image, demonstrates the roof of the maxillary sinus (orbital floor), the lamina papyracea (medial orbital wall), the ethmoid roof (fovea ethmoidalis), and the superior nasal cavity (including the olfactory region and cribriform plate).

T2 signal in the sinonasal region distinguishes the most diagnostically important sinus entities:

• Simple mucus retention / inflammatory mucosal thickening: T2-very bright (water-like)
• Inspissated / proteinaceous secretions: T2-progressively darker as protein concentration increases
• Allergic fungal mucin: T2-dark centre (paramagnetic fungal elements including manganese and iron produce T2 shortening); brighter periphery
• Soft tissue tumour: T2-intermediate (below the T2 of simple fluid; above the T2 of muscle)
• Inverted papilloma: T2-intermediate with characteristic convoluted cerebriform internal architecture
• Vascular tumour (JNA): T2-bright mass with internal flow voids

The T2 coronal is not just a survey sequence — it provides specific diagnostic tissue characterisation that CT cannot.

T2-weighted TSE axial complements the coronal by providing:

• Lateral extent of masses (to the infratemporal fossa, pterygopalatine fossa, masticator space)
• Posterior extent to the nasopharynx, clivus, and sphenoid
• Orbital and intracranial extension
• Skull base anatomy and tumour spread

T1-weighted TSE (non-fat-suppressed) — critical for:

• T1-bright content identification: inspissated haemorrhagic secretions in mucocele appear T1-bright and T2-dark (a specific pattern); fungal mucin may appear T1-bright due to paramagnetic manganese; cholesterol granuloma (in the sinonasal context: sphenoid or maxillary) is T1-bright
• Baseline signal before post-contrast for accurate enhancement assessment: without pre-contrast T1, post-contrast T1-FS cannot be reliably compared for enhancement (T1-bright pre-contrast lesions may appear "enhancing" when they are simply T1-bright)
• Orbital fat signal: pre-contrast T1 shows the normal T1-bright orbital fat that serves as the reference for detecting orbital fat invasion (tumour replaces T1-bright fat with T1-intermediate soft tissue)

Post-contrast T1 fat-suppressed (coronal + axial) — required for:

• Tumour vs secretion distinction: tumour enhances; retained secretions do not
• Perineural spread: enhancement of the infraorbital nerve (CN V2) in the infraorbital canal; enhancement of the descending palatine nerve; pterygopalatine fossa enlargement with enhancement
• Subperiosteal abscess (orbital wall): peripheral ring enhancement of the abscess cavity
• Dural invasion: linear dural enhancement at the skull base
• Mucosal enhancement pattern: normal mucosal enhancement is thin and peripheral; pathological mucosal thickening with enhancement suggests inflammatory or neoplastic disease

Fat suppression is essential because the orbital fat and the fat within the pterygopalatine fossa are normally T1-bright — without fat suppression, enhancing structures within fat-containing spaces are obscured.

DWI — for sinonasal applications:

• Intracranial abscess detection (brain complication of sinusitis): bright on DWI; ADC restricted — this is a standard brain DWI application using conventional EPI
• Sinonasal cholesteatoma / epidermoid: DWI-positive (rare in this location but occurs)
• Distinguishing soft tissue tumour from obstructed secretions in small spaces: tumour typically shows intermediate ADC restriction (1.0–1.5 × 10⁻³ mm²/s); secretions show higher ADC (> 1.5 × 10⁻³ mm²/s)

Important caveat for sinonasal DWI: standard single-shot EPI-DWI has geometric distortion of 5–15 mm at the air-tissue interfaces of the paranasal sinuses — particularly at the ethmoid cells and maxillary sinus. This makes standard EPI-DWI unreliable for intrasinus lesion localisation. For brain complication assessment, standard EPI-DWI is adequate (the brain is less affected by sinus air cells). For intrasinus lesion characterisation, non-EPI DWI (PROPELLER/BLADE or RESOLVE) provides better localisation.

4.4 Sequence Matching and Cross-Sequence Consistency

Pre-contrast T1 and post-contrast T1-FS must use identical geometry (same plane, same FOV, same slice thickness) to enable direct comparison for enhancement assessment. The subtraction image (post minus pre T1) is useful for complex cases where T1-bright pre-contrast content (fungal mucin, haemorrhage) might be misidentified as enhancement.

For serial post-treatment follow-up, the acquisition parameters — particularly the plane, FOV, and slice thickness of the post-contrast T1 coronal — must be reproduced at every follow-up examination for valid comparison.

4.5 Fat Suppression

Post-contrast T1: fat suppression mandatory. SPAIR at isocentre provides adequate fat suppression when the isocentre is correctly positioned at the midface level. At 3T, Dixon post-contrast T1 is preferred for its B0-independence — particularly important at the maxillary sinus level where dental metalwork produces local B0 disturbances.

STIR coronal: for skull base extension assessment, perineural spread, and any situation where SPAIR fails due to off-isocentre positioning or local B0 disturbance, STIR provides reliable fat suppression independent of B0 homogeneity. STIR is the preferred fat suppression technique for any coronal sequence extending from the sinuses to the anterior skull base and orbital apex.

Pre-contrast T1: no fat suppression. The diagnostic value of T1-bright signal content (haemorrhage, fungal mucin, cholesterol) depends on identifying the T1 hyperintensity, which fat suppression would obscure. The natural T1-bright orbital fat is also used as a reference landmark on non-fat-suppressed T1.

Post-contrast STIR is absolutely contraindicated — as throughout all MRIninja protocols.

4.6 Slice Positioning — Complete Technical Reference

Why Precise Sinonasal Positioning Matters

The paranasal sinuses are oriented according to specific anatomical planes that do not correspond to the standard brain axial/coronal planes. The coronal plane is the most diagnostically important for sinonasal imaging — it must be perpendicular to the hard palate (not tilted anteriorly or posteriorly) to show the sinonasal anatomy symmetrically and to allow bilateral comparison.

Anatomical Landmarks

Hard palate: the bony floor of the nasal cavity; forms the reference plane for coronal sinus MRI. The coronal plane should be perpendicular to the hard palate.

Cribriform plate: the roof of the nasal cavity, at the junction of the nasal cavity and the anterior cranial fossa. In sinonasal tumour MRI, the cribriform plate defines the critical boundary between resectable and unresectable disease (dural or intracranial involvement changes management). It must be included in both coronal and axial coverage.

Sphenoid sinus: the most posterior paranasal sinus, bounded by the pituitary fossa superiorly and the clivus posteriorly. Full sinonasal coverage includes the posterior wall of the sphenoid sinus and the clivus. The carotid artery indents the lateral wall of the sphenoid sinus — the relationship of any sphenoid sinus mass to the carotid canal must be documented.

Orbital floor (roof of maxillary sinus): thin bone; frequently dehiscent; a site of direct tumour spread from the maxillary sinus into the orbital fat.

Pterygopalatine fossa: the fat-filled space posterior to the maxillary sinus; contains CN V2 branches (infraorbital nerve), the maxillary artery, and the pterygopalatine ganglion. Perineural spread from palatal/maxillary/nasal tumours enters this fossa and tracks to the foramen rotundum (CN V2) and the inferior orbital fissure. MRI assessment of this fossa requires adequate coronal and axial coverage with fat suppression post-contrast.

Planning Sequence

1. Three-plane localiser
2. Sagittal localiser: used to plan the coronal and axial planes
3. From the sagittal localiser: plan the coronal plane perpendicular to the hard palate (not the brain axial)
4. From the coronal localiser: plan the axial plane parallel to the hard palate
5. Verify that both maxillary sinuses, both orbital floors, the ethmoid complex bilaterally, the cribriform plate, and the sphenoid sinus are within the coverage

Coronal Planning

Reference: sagittal localiser. The coronal plane is defined as perpendicular to the hard palate. This produces a coronal plane that tilts posteriorly by approximately 10–20° compared with the standard brain coronal plane (which is perpendicular to the Reid's baseline).

Coverage: from the anterior wall of the frontal sinus (anteriorly) to the posterior wall of the sphenoid sinus (posteriorly). This 6–8 cm A-P extent covers all paranasal sinuses in coronal sections.

Slice thickness: 3–4 mm for standard sinonasal assessment; 2–3 mm for detailed skull base or orbital floor assessment.

Phase encoding direction: R-L for coronal sequences. The primary artefact sources in the coronal plane are pulsatile flow from the cavernous sinus (R-L displacement of artefacts is away from the sinonasal midline structures) and any dental metalwork artefact.

Axial Planning

Reference: sagittal localiser. The axial plane is parallel to the hard palate — this is the standard sinonasal axial plane, which is approximately parallel to the Frankfurt horizontal plane and the standard brain axial.

Coverage: from below the hard palate (floor of the nasal cavity; alveolar process of the maxilla) to above the frontal sinuses (including the frontal lobes for intracranial complication assessment). Total craniocaudal coverage: approximately 10–12 cm.

Phase encoding direction: A-P for axial sinonasal sequences. Displaces motion artefacts from swallowing and any pulsatile flow anteroposteriorly, away from the sinonasal structures.

Section 4.6 Dedicated Bibliography

Som PM, Curtin HD, editors. Head and Neck Imaging. 5th ed. St. Louis: Mosby; 2011. (Technical / Foundational) — The standard reference text for head and neck MRI including sinonasal anatomy and slice positioning.

Eggesbø HB. Imaging of sinonasal tumours. Cancer Imaging. 2012;12(1):136–152. PMID: 22572484. DOI: 10.1102/1470-7330.2012.0015. (Technical / Foundational) — Systematic review of sinonasal tumour MRI; documents standard coronal and axial positioning requirements and coverage.

5. Optimisation Strategy

5.1 Artefact Reduction by Source

Dental metalwork susceptibility — the primary quality limiting factor for sinonasal MRI in adults:

• Physical cause: ferromagnetic or paramagnetic dental restorations (amalgam, metal alloy crowns, implants) in the upper jaw produce local B0 disturbances extending 3–5 cm at 3T
• Location: affects the posterior maxillary sinus, the pterygopalatine fossa, and the infratemporal fossa
• What it mimics: signal void mimics absent tissue; can obscure a tumour in the posterior maxillary sinus or hide perineural spread in the pterygopalatine fossa
• Reduction: use 1.5T for patients with extensive upper dental metalwork when the pterygopalatine fossa or posterior maxillary sinus is the primary diagnostic target; widen bandwidth (reduces chemical shift but not susceptibility); use STIR instead of SPAIR for fat suppression (more robust near metal)
• When invalidating: if the primary diagnostic question concerns the posterior maxillary sinus or pterygopalatine fossa and this region is obscured by metalwork at 3T, request reimaging at 1.5T

Air-tissue susceptibility at sinus walls: the sinus air-soft tissue interface produces local B0 gradients at all sinus walls. This affects:

• Fat suppression quality at the sinus margins (SPAIR may fail at the interface; Dixon is more robust)
• T2* and SWI signal interpretation near sinus walls
• EPI DWI: geometric distortion at all air-tissue boundaries (as documented in the middle ear protocol — same physics)

Phase artefact from swallowing and pulsatile flow: the A-P phase direction for axial sequences may produce motion ghosting from swallowing. Ask the patient to swallow before each sequence starts but not during the acquisition. For post-contrast dynamic series, respiratory motion and swallowing are the primary motion sources.

Chemical shift at fat-water interfaces: at the pterygopalatine fossa fat-tumour interface and at the orbital fat-tumour interface, chemical shift artefacts can simulate a clean margin or create a false line of demarcation. Use adequate bandwidth (≥ 200 Hz/px at 1.5T; ≥ 400 Hz/px at 3T) to reduce chemical shift artefact to < 1 pixel.

5.2 Protocol Efficiency and Throughput

A complete sinonasal MRI — T2 coronal + T2 axial + T1 axial + post-contrast T1-FS coronal + post-contrast T1-FS axial + DWI — requires approximately 30–40 minutes at 3T.

For staging of sinonasal malignancy, addition of STIR coronal + 3D isotropic post-contrast T1 extends the examination to 45–55 minutes.

For emergency orbital/intracranial complication assessment, the minimum viable examination is: T2 coronal + T2 axial + post-contrast T1-FS coronal + DWI (brain coverage) — approximately 15–20 minutes.

5.3 Field Strength Considerations

3T advantages: higher SNR enables thinner slices (2–3 mm vs 3–4 mm at 1.5T); better soft tissue contrast for tumour characterisation; superior Dixon fat suppression at 3T.

1.5T advantages for sinonasal MRI:

• Significantly smaller susceptibility artefacts from dental metalwork — 1.5T is strongly preferred for patients with posterior upper dental metalwork when the pterygopalatine fossa is the diagnostic target
• Less severe air-tissue susceptibility at sinus walls
• More reliable SPAIR fat suppression at the sinonasal level (reduced B0 inhomogeneity)

Practical department decision: for routine sinonasal tumour staging in patients without extensive dental metalwork, 3T is preferred. For patients with upper posterior dental metalwork, 1.5T provides better image quality in the critical pterygopalatine fossa and posterior maxillary sinus regions.

6. Contrast Use Principles Specific to Paranasal Sinus MRI

6.1 Non-Contrast Standard Protocol — Sufficient For

Non-contrast sinonasal MRI (T2 coronal + T2 axial + T1 axial + DWI) is diagnostically adequate for:

• Initial characterisation of sinus content type (mucus vs soft tissue vs fungal mucin) when tumour has been excluded
• Mucocele characterisation (T2-bright to T2-intermediate; T1-variable based on protein content; no enhancement needed for diagnosis)
• Inverted papilloma initial characterisation (T2 cerebriform pattern)
• Sinonasal polyps (T2-very bright; no enhancement needed for diagnosis)
• Assessment of sinonasal anatomy after conservative FESS without tumour concern

6.2 Gadolinium Indicated — Region-Specific Contexts

Post-contrast T1-FS is required for:

• Any suspected sinonasal malignancy: tumour enhancement vs non-enhancing obstructed secretions is the key distinction for staging; gadolinium is mandatory
• Orbital or intracranial complication of sinusitis: subperiosteal abscess (ring enhancement); dural enhancement; cerebral abscess (ring enhancement)
• Perineural spread assessment: CN V2 infraorbital nerve and pterygopalatine fossa enhancement is the primary PNS sign
• Inverted papilloma pre-operative staging: extent of mucosal attachment and enhancement pattern guides surgical approach
• Angiofibroma (JNA): hypervascular tumour shows intense early enhancement; contrast is essential for characterisation and staging
• Post-treatment follow-up for sinonasal malignancy: distinguishing residual/recurrent tumour (enhancing) from fibrosis and post-treatment change (enhancing early, fading late)
• Fungal sinusitis in immunocompromised patients: mucosal enhancement loss (necrosis) is the critical sign of invasive fungal sinusitis — requires contrast

6.3 Post-Contrast Acquisition Timing

Standard equilibrium phase (3–5 minutes post-injection). No specific arterial phase is required for the generic protocol.

For angiofibroma (JNA) vascular characterisation: early dynamic post-contrast phase (20–30 seconds post-injection) demonstrates the intense arterial-phase enhancement specific to this hypervascular tumour. This is part of the dedicated JNA child protocol.

7. Reporting Essentials

7.1 Interpretation Framework

Sinonasal MRI reporting follows a systematic compartmental approach:

Primary question: what type of sinus content?

• Air: normal
• Mucus retention (T2-bright, no enhancement, thin mucosal rim): inflammatory, obstructive
• Soft tissue (T2-intermediate, enhances): tumour, granuloma, inspissated secretion
• Fungal mucin (T2-dark centre, T1-variable, specific distribution): allergic fungal sinusitis, saprophytic colonisation
• T1-bright content (haemorrhagic mucus, cholesterol, protein): mucocele, haemorrhagic polyp, fungal mucin

Secondary question: extent and invasion

• Confined to sinus (T1 stage)
• Sinus expansion / bony thinning / bony erosion (T2 stage — CT confirms bony detail)
• Orbital fat invasion (T3): T1-bright orbital fat replaced by intermediate signal tumour
• Dural invasion or intracranial extension (T4): dural enhancement; brain parenchymal T2 signal; leptomeningeal enhancement
• Pterygoid plate and masticator space involvement
• Perineural spread: pterygopalatine fossa signal loss + enhancement; infraorbital nerve thickening/enhancement

Differential framework for sinonasal mass:

• T2-very bright + no enhancement + smooth walls → mucus retention / simple polyps
• T2-dark centre + no enhancement → fungal (allergic/saprophytic)
• T2-intermediate + enhances + unilateral + mass-like → tumour (SCC, adenocarcinoma, sarcoma)
• T2-intermediate + enhances + convoluted cerebriform pattern → inverted papilloma
• T2-bright + intense enhancement + flow voids → JNA (young male)
• T2-intermediate + heterogeneous + "salt and pepper" → paraganglioma (rare)

7.2 Mandatory Reporting Checklist

Technical quality:

• Field strength; coil; isocentre position (midface vs brain)
• Dental metalwork artefact: absent / present — specifying affected region
• Fat suppression quality in the pterygopalatine fossa and orbital fat: adequate / impaired
• Contrast: if given — agent, dose, timing

Bilateral systematic review:

• Maxillary sinuses: normal / opacification (characterise signal: T2, T1, DWI, enhancement)
• Ethmoid complex: normal / opacification; unilateral / bilateral
• Frontal sinuses: normal / opacification; bilateral coverage confirmed
• Sphenoid sinus: normal / opacification; carotid canal intact bilateral
• Nasal cavity: normal / mass / polyps (bilateral)

Critical extension assessment (for any soft tissue mass):

• Orbital floor: intact / defect / tumour extension into orbital fat
• Lamina papyracea: intact / dehiscent / eroded
• Cribriform plate: intact / erosion (report as T4 staging implication)
• Skull base: intact / erosion / intracranial extension
• Pterygoid plates: intact / eroded
• Pterygopalatine fossa: normal fat / abnormal signal / enhancement (PNS)
• Infraorbital nerve: normal / thickened / enhanced (PNS CN V2)

7.3 Structured Reporting

Reports must include: Indication (mass characterisation / staging / complication / post-treatment); Technique (field strength, coil, sequences, isocentre, contrast); Comparison (prior imaging); Findings (bilateral systematic review + extension assessment); Impression (primary finding; staging if malignancy; DWI conclusion; complication if present); Limitations (dental metalwork artefact; region affected; fat suppression failure).

7.4 Incidental Findings — Clinical Decision Framework

Usually benign: incidental mucosal thickening < 3 mm in a single sinus without symptoms (common, not clinically significant); small mucus retention cyst of the maxillary sinus floor (extremely common — present in 10–25% of the general population; benign, no follow-up needed unless enlarging or symptomatic); bilateral symmetric mucosal thickening in the context of an upper respiratory illness.

May require clinical correlation: unilateral complete sinus opacification without known inflammatory disease (may represent mucocele, obstructing tumour, or post-traumatic change); T2-dark material in a sinus (consider fungal colonisation; ENT assessment).

Urgent communication: unexpected intracranial extension of a sinonasal mass; unexpected intracranial complication (abscess, epidural collection); unexpected loss of mucosal enhancement in a sinus in an immunocompromised patient (invasive fungal sinusitis — medical emergency).

8. MRI Technologist Pearls

8.1 Sequence Order Logic

1. Three-plane localiser + sagittal survey for coronal plane planning
2. T2 coronal ← primary diagnostic sequence; plan first with hard palate reference
3. T2 axial
4. T1 axial ← pre-contrast reference; no fat suppression
5. DWI
6. Contrast injection (if indicated)
7. Post-contrast T1-FS coronal ← primary post-contrast diagnostic sequence
8. Post-contrast T1-FS axial

The T2 coronal is placed first because it is the most diagnostically informative sequence and is motion-sensitive. If the patient cannot complete the full protocol, the T2 coronal and post-contrast T1-FS coronal provide the most clinical information per unit time.

8.2 Positioning Tricks

Isocentre at midface, not at brain: lower the table so that the nasal bridge is at the isocentre rather than the top of the head. This single adjustment is the most impactful positioning decision for sinonasal MRI — it directly determines fat suppression quality in the maxillary sinus and pterygopalatine fossa.

Verify the coronal plane on the sagittal localiser: the coronal plane must be perpendicular to the hard palate, not to the brain orbitomeatal line. These differ by 10–20°. A coronal plane tilted forward (parallel to the brain coronal) shows the sinonasal structures asymmetrically and makes bilateral comparison difficult.

Patient breath-holding for specific sequences: swallowing artefacts in the A-P direction degrade axial sinonasal sequences. Instructing the patient to swallow immediately before each axial sequence starts and then remain still (with no swallowing) during the 3–4 minute acquisition reduces artefact.

8.3 Fast Salvage Protocol

Approximately 9–11 minutes — covers the primary diagnostic questions.

8.4 Common Avoidable Errors

9. Quality Control Checklist

• Isocentre at midface level (nasal bridge); not at standard brain position
• Coronal plane: verified perpendicular to hard palate on sagittal localiser
• Axial plane: parallel to hard palate
• Coverage: frontal sinus (anteriorly) through sphenoid posterior wall (posteriorly) in coronal sequences
• Coverage: hard palate floor through frontal lobe in axial sequences (for intracranial complication exclusion)
• T2 coronal: bilateral maxillary, ethmoid, frontal sinuses visible; cribriform plate included
• T2 axial: both pterygopalatine fossae visible; sphenoid sinus included
• T1 axial pre-contrast: no fat suppression; pterygopalatine fossa fat signal visible bilateral
• Post-contrast T1-FS: fat suppression quality — uniform at maxillary level / impaired (document)
• Dental metalwork artefact: assessed and documented; affected region specified
• DWI: ADC map generated
• If contrast: injection time documented; timing 3–5 min post-injection

10. Advanced Technical Parameters

10.1 T2-Weighted TSE Coronal — Sinonasal Specific

Tissue Contrast Logic

The T2-weighted coronal TSE is the central diagnostic sequence for sinonasal pathology because T2 signal intensity distinguishes the most important clinical entities in a way no other MRI sequence can. The T2 signal of sinus content directly reflects the physical-chemical properties of the material:

• Free water (simple mucus, serous secretion, oedematous mucosa): T2 ~ 1000–2000 ms → very bright
• Intermediate protein concentration (thick mucus, 15–25% protein): T2 ~ 200–500 ms → moderately bright
• High protein concentration / inspissated secretions (> 25–30% protein): T2 < 100 ms → progressively dark
• Fungal concretions (allergic fungal mucin: dense mucin with paramagnetic heavy metals — iron, manganese from fungal metabolism): T2 < 50 ms → very dark; may appear signal-void
• Soft tissue tumour (intermediate cellular material, moderate water content): T2 ~ 50–100 ms → intermediate; distinctly less bright than simple fluid

This T2 stratification allows direct tissue characterisation without biopsy for the most common diagnostic scenarios.

Key Parameters

10.2 Post-Contrast T1 Fat-Suppressed — Sinonasal Specific

The post-contrast T1-FS must reliably suppress the orbital fat (T1-bright) and the pterygopalatine fossa fat to reveal enhancing structures within these fat-containing spaces. The choice of fat suppression technique is the most important technical decision for the post-contrast sinonasal T1:

SPAIR (at isocentre = midface): provides reliable spectral fat suppression when the sinonasal region is at the B0 field centre. Fails adjacent to dental metalwork.

Dixon: water-fat separation algorithm; B0-inhomogeneity independent; most robust for the sinonasal region, particularly at 3T. The preferred technique when dental metalwork is present or when SPAIR has failed in prior examinations.

STIR post-contrast: absolutely contraindicated (as throughout MRIninja protocols).

Section 10 Dedicated Bibliography

Eggesbø HB. Imaging of sinonasal tumours. Cancer Imaging. 2012;12(1):136–152. PMID: 22572484. DOI: 10.1102/1470-7330.2012.0015. (Technical / Foundational) MRI and CT protocols for sinonasal tumour characterisation and staging; T2 tissue characterisation principles; fat suppression for post-contrast T1.

Bhatt AA, Cross JM. Sinonasal masses. Semin Ultrasound CT MR. 2018;39(5):419–431. PMID: 30342611. DOI: 10.1053/j.sult.2018.06.001. (Technical / Moderate) MRI characterisation of sinonasal masses; T2 signal stratification for tissue diagnosis; inverted papilloma cerebriform pattern.

11. Evidence Gaps and Ongoing Debate

MRI vs CT primary modality for sinonasal mass: no large prospective trial has formally compared MRI and CT as the primary modality for sinonasal mass characterisation against a pathological reference standard. Current practice (CT for anatomy + MRI for soft tissue characterisation) is based on expert consensus and retrospective series rather than formal evidence.

Inverted papilloma T2 cerebriform pattern — sensitivity and specificity: multiple retrospective series have reported sensitivity 70–90% and specificity 80–95% for the convoluted cerebriform T2 pattern in identifying inverted papilloma. These figures are from experienced centres; community radiology performance may be lower. No multi-centre prospective validation against surgical pathology exists.

DWI for sinonasal tumour characterisation: ADC values have been reported as useful for distinguishing sinonasal squamous cell carcinoma (lower ADC) from lymphoma (lower ADC) from inverted papilloma (intermediate ADC) from inflammatory disease (higher ADC). However, the overlap between categories is significant and no consensus ADC thresholds have been validated for clinical decision-making.

3T vs 1.5T for sinonasal tumour staging: the superior SNR of 3T is partially offset by greater susceptibility from dental metalwork. No prospective comparative study has established which field strength provides superior staging accuracy for sinonasal malignancy in an unselected patient population (which includes many patients with dental metalwork).

AI-based tumour segmentation and staging: automated sinonasal tumour segmentation and T-stage classification from MRI has been described in research publications. No clinically validated, regulatory-cleared AI tool exists for routine sinonasal tumour staging at the time of writing.

12. Evidence-Based References

A. Guidelines / Consensus / Society Recommendations

B. Systematic Reviews / Meta-analyses

(No dedicated systematic reviews address the generic sinonasal MRI protocol as a primary subject; evidence is primarily from imaging characterisation studies and retrospective series.)

C. Important Prospective / Original Studies

D. Technical MRI Papers

End of document — MRI Paranasal Sinuses Generic Standard Protocol — MRIninja v1.0 — May 2026 Related pages: MRI Cranial Nerves Generic Standard Protocol · MRI Soft Tissues Neck Generic Standard Protocol · MRI Orbit Generic Standard Protocol This master page is the reference for all future sinonasal child pages including: sinonasal malignancy staging (SCC, adenocarcinoma, olfactory neuroblastoma, SNUC); inverted papilloma characterisation and recurrence; juvenile nasopharyngeal angiofibroma; invasive fungal sinusitis; orbital complication of sinusitis; intracranial complication of sinusitis; sinonasal lymphoma; post-treatment surveillance.