有多少“四边孔综合征”被漏诊？
四边孔综合征（QSS）是一个不常见的诊断，主要是因为缺乏相关文献、存在误诊。
（ 鼎湖影像补充：四边孔是由小圆肌、大圆肌、肱三头肌长头和肱骨颈内侧缘组成的解剖间隙。大小圆肌之间有一层筋膜组织，腋神经从后束发出后即斜向后行，贴四边孔上缘穿出该孔沿三角肌深层继续向外向前行走，支配肩背外侧皮肤感觉的皮支穿出肌肉进入皮下。当肩关节外展、外旋时，大、小圆肌和肱三头肌长头均受到牵拉，从上方、下方及内侧对四边孔产生压迫。）
Epidemiology
QSS is present on ~1% of shoulder MRIs .
流行病学
1%肩关节MRI病人存在QSS
Clinical presentation
Patients present with posterior shoulder pain and paresthesia over the lateral arm .
临床症状
病人表现为肩后疼痛和上臂外侧感觉异常。
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是神经血管压迫综合征，是旋肱后动脉（PHCA）和（或）腋神经或腋神经主要分支（臂外上皮神经）在四边孔处受压后所引起的临床症候群。
QSS通常见于神经血管束在四边孔内被纤维束带和/或肥大的肌肉压迫。
纤维束带通常是由于创伤导致形成疤痕和粘连。在投掷运动员，网球运动员和上臂运动为主排球运动员的病例报道中支持纤维化和肌肉肥厚为病因的假说。
已有报道腋神经分支的变异和先天的小四边孔间隙更易于出现QSS。这种情况的病例报道较少。
QSS的其它病因：
急性创伤，例：挤压和牵引伤
腱鞘囊肿
下关节盂唇撕裂导致的囊肿
旋肱后动脉瘤或外伤性假性动脉瘤
肿瘤，例如肱骨骨软骨瘤
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.
影像学表现：
MRI
MRI是首选的检查，表现为小圆肌和/或三角肌的萎缩+/-脂肪浸润。文献综述显示不同程度的三角肌和小圆肌的不同程度的受累。
除非四边孔（QS）有病变，否则四边孔并不总是在MR上显示。
MR Arthrogram showing a typical inferior paralabral cyst associated with a labral tear, causing QSS
MRI Scan showing atrophy of Teres Minor（小圆肌萎缩）
血管造影 - DSA
在MR出现之前，常规血管造影是主要的诊断方式。血管造影将显示QS区域的后旋肱后动脉闭塞或压迫。
An angiogram of a patient with quadrilateral space syndrome.A, Digital subtraction angiogram with arm in adductionreveals patent posterior humeral circumflex artery. B, Angiogram of same patient with the arm in abduction reveals complete occlusion of the posterior humeral circumflex artery (arrow), confirming the diagnosis.同一病人上臂内收（A）与外展（B）时造影，B图箭头示旋肱后动脉完全闭塞。
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