Types of laryngocele:
1-Internal: confined to larynx.
2-Mixed : has internal and external components. The lesion herniates
through thyrohyoid membrane into anterior soft tissue of neck.
3-Secondary: internal or mixed due to obstructing lesion e.g. tumor
or postinflammatory stenosis.
4-Pyolaryngocele: internal or mixed with superinfection.

The above case shows primary (no obstructive lesion), mixed (intra- and extra- laryngeal) pyolaryngocele (infected laryngocele). An isthmus or waist through the perforated thyrohyoid membrane is noted (red arrows in coronal reformat). The laryngeal airway was compressed by the lesion (green arrow in axial). The patient presented acutely needing urgent tracheostomy followed by surgical excision.

Reference: Harnsberger R et al. Diagnostic Imaging: Head & NeckAmirsys 2004

Credit: Dr Ahmed Haroun