Quadrangular space syndrome
(QSS)
is an uncommon diagnosis mainly because of lack of literature on the subject and possible misdiagnosis。
四邊孔綜合徵（QSS）
是一個不常見的診斷，主要是因為缺乏相關文獻、存在誤診。
（ 鼎湖影像補充：四邊孔是由小
圓肌、大圓肌、肱三頭肌長頭和肱骨頸內側緣
組成的解剖間隙。大小圓肌之間有一層筋膜組織，腋神經從後束髮出後即斜向後行，貼四邊孔上緣穿出該孔沿三角肌深層繼續向外向前行走，支配肩背外側面板感覺的皮支穿出肌肉進入皮下。當肩關節外展、外旋時，大、小圓肌和肱三頭肌長頭均受到牽拉，從上方、下方及內側對四邊孔產生壓迫。）
Epidemiology
QSS is present on ~1% of shoulder MRIs 。
流行病學
1%肩關節MRI病人存在QSS
Clinical presentation
Patients present with posterior shoulder pain and paresthesiaover the lateral arm 。
臨床症狀
病人表現為肩後疼痛和上臂外側感覺異常。
Pathology
QSS is a neurovascular compression syndrome of the posterior humeral circumflex artery （PHCA） and/or the axillary nerve or one of its major branches in the quadrangular space。
QSS most commonly occurs when the neurovascular bundle is compressed by fibrotic bands within the QS and/or by hypertrophy of the muscle boundaries。
Fibrotic bands form as the result of trauma， with resultant scarring and adhesions。 Cases reported in throwing athletes， tennis players， and in the dominant arm of volleyball players support the fibrosis and hypertrophy based hypotheses。
Variation in axillary nerve division and a genetically smaller QS have been hypothesised to predispose to QSS。 This may account for the limited number of reported cases。
Other reported cases of QSS include：
acute trauma， e。g。 crush or traction injury
ganglion cyst
paralabral cyst arising from a detached inferior glenoid labral tear
aneurysms and traumatic pseudoaneurysms of posterior humeral circumflex artery
tumours， e。g。 humeral osteochondroma
病理：
QSS
是神經血管壓迫綜合徵，是旋肱後動脈（PHCA）和（或）腋神經或腋神經主要分支（臂外上皮神經）在四邊孔處受壓後所引起的臨床症候群。
QSS
通常見於神經血管束在四邊孔內被纖維束帶和/或肥大的肌肉壓迫。
纖維束帶通常是由於創傷導致形成疤痕和粘連。在投擲運動員，網球運動員和上臂運動為主排球運動員的病例報道中支援纖維化和肌肉肥厚為病因的假說。
已有報道腋神經分支的變異和先天的小四邊孔間隙更易於出現QSS。這種情況的病例報道較少。
QSS的其它病因：
急性創傷，例：擠壓和牽引傷
腱鞘囊腫
下關節盂唇撕裂導致的囊腫
旋肱後動脈瘤或外傷性假性動脈瘤
腫瘤，例如肱骨骨軟骨瘤
Radiographic features
MRI
MRI is the investigation of choice， demonstrating atrophy +/- fatty infiltration in the teres minor and/or deltoid muscle。 Literature review has shown varying proportions of deltoid and teres minor involvement。
Direct MR imaging of the QS is not always possible， unless there is a lesion in QS。
Angiography - DSA
Before the advent of MR conventional angiography was the primary diagnostic modality。 Angiography would show occlusion or compression of the posterior circumflex artery in the QS region。
影像學表現：
MRI
MRI是首選的檢查，表現為小圓肌和/或三角肌的萎縮+/-脂肪浸潤。文獻綜述顯示不同程度的三角肌和小圓肌的不同程度的受累。
除非四邊孔（QS）有病變，否則四邊孔並不總是在MR上顯示。
MR Arthrogram showing a typical inferior paralabral cyst associated with a labral tear， causing QSS
MRI Scan showing atrophy of Teres Minor（小圓肌萎縮）
血管造影 - DSA
在MR出現之前，常規血管造影是主要的診斷方式。血管造影將顯示QS區域的後旋肱後動脈閉塞或壓迫。
An angiogram of a patient with quadrilateral space syndrome。A，Digital subtraction angiogram witharminadductionreveals patent posterior humeral circumflex artery。 B， Angiogram ofsamepatient with the arm in abduction reveals complete occlusion of the posterior humeral circumflex artery （arrow）， confirming the diagnosis。
同一病人上臂內收（A）與外展（B）時造影，B圖箭頭示旋肱後動脈完全閉塞。
Treatment and prognosis
Treatment is initially conservative if no cause is found。 Refractory cases require surgery。 If a definitive lesion in the QS is demonstrated on MR then primary surgery can be undertaken。
The identification of MRI findings of QSS and the exclusion of other treatable abnormalities in the shoulder may allow institution of appropriate nonsurgical therapy for QSS to be followed potentially by surgical treatment in some refractory cases。 Even if other shoulder abnormalities are present， findings of QSS may provide an explanation for some of the patients who have persistent discomfort after treatment of the primary shoulder abnormality。
Differential diagnosis
On imaging consider
disuse atrophy which will show multiple muscle involvement around the shoulder and not just teres minor / deltoid
Parsonage-Turner syndrome may be distinguished from QSS on MRI by the usual involvement of more than one muscle or even more than one nerve distribution
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