Masticator Space Blow-out: A previously unappreciated maxillary sinus fracture. Erly, W. MD Inampudi, R. MD Becker, J. MD Nael, K. MD Hur, J. MD Kubal, W. MD University of Arizona Tucson, AZ

Masticator Space Blow-out Fracture Segmental, depressed fractures of the lateral maxillary sinus may occur as a result of trauma to the masticator space, frequently in conjunction with other regional fractures. This paper defines the fracture and estimates its incidence.

Masticator Blow-out Fracture Axial CT at the level of the midface shows depressed, segmental fracture of the lateral maxillary sinus with herniation of muscle and fat into the sinus.

Masticator Blow-out Fracture Direct blow to left mandible. No other fractures present.

Masticator Blow-out Fracture At the level of the zygomatic arch, the masticator space is confined by the maxillary sinus, central skull base and floor of the middle cranial fossa. An increase in pressure can result in a fracture of the lateral maxillary sinus wall, the weakest point.

Masticator Blow-out Fracture Below the central skull base, the masticator space opens medially to the parapharyngeal space allowing egress of a pressure wave medially.

Masticator Blow-out Fracture Masticator blowout fracture was defined as a segmental fracture in the lateral aspect of the maxillary sinus with medial displacement of lateral maxillary bone fragments accompanied by herniation of a variable amount of masticator space fat and/or muscle into the maxillary sinus. This retrospective study is HIPAA compliant and IRB approved.

Masticator Blow-out Fracture The University of Arizona Hospital electronic medical records were searched from January 1, 2014 to November 30, 2014 for the key words: zygoma, zygomatic, ZMC, tripod, mandible, and mandibular. Penetrating trauma, including gunshot wounds were excluded.

Masticator Blow-out Fracture Ten of 40 (25%) ZMC fractures had a masticator blow out fracture. The authors hypothesize that the fat herniation is related to the transient increase in pressure within the masticator space.

Masticator Blow-out Fracture Five of 89 (5.6%) of the mandibular fractures had an associated lateral maxillary sinus fracture

Masticator Blow-out Fracture 6 of 49(12.2%) zygomatic arch fractures had an associated masticator space blow-out fracture.

Masticator Blow-out Fracture Conclusion: Masticator space blow-out fracture, defined as a segmental depressed fracture of the lateral maxillary sinus is relatively common. The authors hypothesize that it is due to a transient increase in pressure in the masticator space and is a separate entity from other fractures of the region that may occur concurrently.