ction , ▁extension , ▁external ▁rotation ▁and ▁overhead ▁activity . ▁Select ive ▁at ro phy ▁of ▁the ▁ter es ▁minor ▁mus cle ▁has ▁been ▁seen ▁and ▁pulled ▁together ▁directly ▁with ▁compression ▁of ▁the ▁corresponding ▁ax ill ary ▁n erve ▁branch ▁or ▁posterior ▁hum eral ▁circum flex ▁ar tery . ▁F ibr ous ▁bands , ▁c yst s ▁of ▁the ▁g len oid ▁lab rum , ▁lip oma ▁or ▁dil ated ▁ve ins ▁can ▁occup y ▁the ▁quad ril ater al ▁space ▁path olog ically . ▁Similar ▁sympt oms ▁are ▁common ▁with ▁anterior ▁shoulder ▁dis location , ▁hum eral ▁neck ▁f ract ure , ▁bra ch ial ▁p lex us ▁injury ▁and ▁thor ac ic ▁out let ▁and ▁in let ▁synd rome . ▁It ▁is ▁important ▁to ▁include ▁those ▁path ologies ▁for ▁a ▁complete ▁as ▁possible ▁differential ▁diagn osis . ▁ ▁Ul tr ason ography ▁is ▁a ▁tool ▁to ▁detect ▁a ▁fat ty ▁deg ener ative ▁at ro phy ▁of ▁the ▁ter es ▁minor ▁and ▁shows ▁in ▁affected ▁mus cles ▁increased ▁e ch ogen icity ▁and ▁bet imes ▁a ▁slight ▁reduction ▁in ▁mus cle ▁bulk . ▁MR ▁imag ing ▁helps ▁to ▁cons olid ate ▁the ▁diagn osis ▁of ▁ne uro gen ic ▁mus cle ▁at ro phy . ▁Ext rac ell ular ▁ed ema ▁after ▁tra um atic ▁events ▁causing ▁neural ▁damage ▁show ▁an ▁increased ▁signal ▁intensity ▁on ▁T 2 - weight ed ▁M RI ▁sequences ▁and ▁normal ▁intensity ▁on ▁T 1 - weight ed ▁sequences . ▁Post er ior ▁hum eral ▁circum flex