Not every encephalocele creates a visible bump. Basal and transsphenoidal encephaloceles are skull-base defects where the sac protrudes inward toward the nose, sinuses, or throat — so there may be nothing to see from the outside. This makes them the most likely to be missed.
What these are
Basal encephaloceles occur through the bones of the skull base. Transsphenoidal encephaloceles, a specific rare subtype, extend through the sphenoid bone and can project into the upper throat (pharynx) or nasal cavity. Because they're internal, they can go undetected for a long time.
How they present
Instead of a visible sac, hidden encephaloceles may show up as:
- A mass inside the nose or upper throat
- Nasal obstruction or chronic nasal blockage
- Snoring or breathing difficulty
- Clear fluid drainage from the nose (a possible cerebrospinal fluid leak)
- Recurrent meningitis (infection of the brain's coverings)
- Wide-set eyes or other midline facial features in some cases
A child with unexplained nasal blockage, recurrent CSF-like nasal drainage, or repeated meningitis may be evaluated for a hidden skull-base encephalocele.
Why they're dangerous if missed
A skull-base encephalocele can create an open pathway between the brain's fluid spaces and the nose or sinuses. That pathway can leak cerebrospinal fluid and allow bacteria to travel upward, causing meningitis. This is the central reason these defects must be correctly identified and repaired, and why a suspicious intranasal mass should never be biopsied before imaging.
Diagnosis and treatment
Diagnosis relies on MRI (soft tissue and brain connection) and CT (the bony skull-base defect). Treatment is surgical, with the goals of sealing the defect and creating a watertight barrier. Many skull-base encephaloceles are well suited to endoscopic endonasal (through-the-nose) repair, which avoids external incisions.
Sources
- StatPearls (NCBI Bookshelf) — Encephalocele (basal/transsphenoidal)
- Endoscopic endonasal skull base repair literature (PMC)
- ScienceDirect (Topics) — Encephalocele overview
- Cleveland Clinic — Encephalocele