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Sinonasal Maldevelopmental Lesions: One Event, One Family

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

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Core clinical idea

One developmental event explains the whole family: a dural diverticulum dips into the prenasal space behind the nasal bone and normally regresses (leaving the foramen cecum). Persist = encephalocele, pinch off = glial heterotopia, drag ectoderm back = dermal sinus/dermoid. All are cranionasal, so any superior nasal mass abutting the anterior fossa must have its cribriform/fovea ethmoidalis cleared before it is called benign.

Bottom line

One dural diverticulum explains encephalocele, glial heterotopia, and dermal sinus — and every superior nasal mass gets its anterior fossa floor cleared before it's called benign.

Core workstation questions

  • Is the cribriform/fovea ethmoidalis intact, or is this superior nasal mass continuous with an anterior fossa defect?
  • Which mechanism fits — herniating CNS (encephalocele), pinched-off CNS over the dorsum (glial heterotopia), or a tract/dermoid to the foramen cecum (dermal sinus)?
  • For an encephalocele, what are the roof and floor (naming), and is this the sneaky intranasal nasoethmoidal one?
  • For a dermal sinus, how far intracranially does the tract go (full-resection planning)?
  • Sphenoid wing dysplasia — are there other NF1 features, and is a small greater-wing defect just benign fat herniation rather than tumor/trauma?

What changes reporting / management

  • Prove the cribriform plate/fovea ethmoidalis is intact on any superior nasal mass; a defect raises encephalocele and should stop blind transnasal biopsy/resection.
  • Name encephaloceles roof-first/floor-second (frontonasal, nasoethmoidal) and specifically flag the adult intranasal nasoethmoidal encephalocele masquerading as a polyp.
  • Trace a nasal dermal sinus/dermoid to the foramen cecum and report full intracranial extent for complete resection.
  • Recognize sphenoid wing dysplasia (empty orbit, temporal lobe/subarachnoid herniation, pulsatile proptosis), link to NF1, and don't mistake a small benign greater-wing fat-herniation defect for tumor/trauma.

Practical traps

  • Calling herniated or heterotopic CNS tissue a polyp and biopsying it.
  • Missing the intranasal nasoethmoidal encephalocele in an adult superior nasal mass.
  • Labeling glial heterotopia a 'nasal glioma'/neoplasm (it is GFAP/S100-positive heterotopic glial tissue, often gliotic).
  • Confusing a small greater-wing fat-herniation defect with post-traumatic or neoplastic disease.

Teaching pearls

  • Persist = encephalocele, pinch off = glial heterotopia, drag ectoderm = dermal sinus — one mechanism, three lesions.
  • The adult intranasal nasoethmoidal encephalocele is the polyp that's actually brain — check the cribriform plate.
  • 'Nasal glioma' is heterotopic glial tissue (GFAP/S100+), not a tumor.
  • Resect the nasal dermal sinus tract in full to the foramen cecum, or it recurs.
  • Sphenoid wing dysplasia (empty orbit, pulsatile proptosis) — think NF1, and don't confuse a fat-herniation defect for tumor.

Teaching visuals

Sinonasal maldevelopmental lesions — one dural diverticulum, three lesionsRealistic midline sagittal base + vector overlay — conceptual teaching aid, not a radiographsuperior ↑ ← anterior (face)inferior ↓Cribriform plate / fossa flooranterior cranial fossa floor; brain & meninges aboveForamen cecummidline gap the diverticulum dips throughPrenasal spacenasal bone ↔ cartilage, in front of cribriform plateDural diverticulumdescends through foramen cecum, then regresses→ normally leaves only the foramen cecumWhat happens to it?persist · pinch off · drag ectoderm back→ three outcomes →1 · PERSISTS → ENCEPHALOCELEBrain/meninges herniate through a skull-base defect,STILL connected intracranially(frontonasal or nasoethmoidal).2 · PINCHES OFF → NASAL GLIAL HETEROTOPIALoses intracranial link → isolated rest of glialtissue (GFAP/S100+). NOT a tumor —"nasal glioma" is a MISNOMER.No or only a tiny fibrous connection.3 · DRAGS ECTODERM → DERMAL SINUS / DERMOIDDiverticulum drags ectoderm back along the tract→ ectoderm-lined sinus/cyst that can run fromskin to the foramen cecum.Key reporting pointsCLEAR the anterior fossa floor (cribriform plate /fovea ethmoidalis) on every superior nasal mass beforecalling it benign or biopsying — a floor defect raisesencephalocele and STOPS a blind transnasal biopsy.Adult intranasal nasoethmoidal encephalocele ="the polyp that's actually brain."Trace a dermal sinus fully to the foramen cecum — anincompletely traced tract recurs.Bottom linePersist = encephalocele · Pinch off = glial heterotopia · Drag ectoderm = dermal sinus/dermoid.Clear the cribriform plate before you call a superior nasal mass benign.
Sinonasal Maldevelopmental Lesions — One Dural Diverticulum, Three Lesions

Source lectures

  • Sinonasal Maldevelopmental Lesions

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.