
10
FACIAL WEAKNESS
Facial asymmetry
can be produced by structural abnormalities or by unilateral or asymmetrical
weakness of the muscles of the face. Structural abnormalities are due
to musculoskeletal deformations, soft tissue masses, and tumors. The weak
muscles involved in the production of facial asymmetry are the: (1) facial
mimetic muscles; (2) levator palpebrae muscles; or (3) muscles of Müller.
The distinction between functional
and structural facial asymmetry can be made by observation. Structural
facial asymmetry is diagnosed by observing a physical cause for the facial
asymmetry. Functional asymmetry is diagnosed by the absence of a physical
deformity. The neurogenic system involved in functional asymmetries can
be determined by the area of the face involved, the degree of asymmetry
at different behavioral stages (crying and quiet awake), and the presence
of associated neurological and general findings. (Figure 169.1) Facial
asymmetry due to muscle weakness (functional) will disappear when the
weak muscle is not being used. This occurs because the facial mimetic
muscles, levator palpebrae muscles (common oculomotor system), and the
muscles of Müller (oculosympathetic system) are bilateral and usually
have synchronous and symmetrical activity.
Figure 169.1.—
Differential diagnosis of neurogenic facial asymmetry. Diagonal blue-line
area indicates area of the face involved. CN: cranial nerve; DAOM: depressor
angularis oris muscle; M: muscle; SYMP: sympathetic; ABN: abnormality;
SYST: system.
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