Quadrangular space syndrome

Quadrangular space syndrome also known as quadrilateral space syndrome is an uncommon diagnosis mainly because of lack of literature on the subject and possible misdiagnosis.

Epidemiology

Quadrangular space syndrome is present on ~1% of shoulder MRIs ⁶. 

Clinical presentation

Patients present with posterior shoulder pain and paresthesiaover the lateral arm ⁵.

Pathology

Quadrangular space syndrome 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.

Quadrangular space syndrome most commonly occurs when the neurovascular bundle is compressed by fibrotic bands within the quadrangular space 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 quadrangular space have been hypothesised to predispose to quadrangular space syndrome. This may account for the limited number of reported cases.

Other reported cases of quadrangular space syndrome include:

• acute trauma, e.g. crush or traction injury ⁵
• ganglion cyst
• paralabral cyst arising from a detached inferior glenoid labral tear
• aneurysms and traumatic pseudoaneurysms of posterior circumflex artery
• tumours, e.g. humeral osteochondroma

Radiographic features

MRI

MRI is the investigation of choice, demonstrating atrophy +/- fatty infiltration in the teres minor and/or deltoid muscle. A literature review has shown varying proportions of deltoid and teres minor involvement.

Direct MR imaging of the quadrangular space is not always possible unless there is a focal lesion.

Angiography - DSA(DSA)

Before the advent of MRMRI, conventional angiography was the primary diagnostic modality. Angiography would show occlusion or compression of the posterior circumflex artery in the quadrangular space region.

Treatment and prognosis

Treatment is initially conservative if no cause is found. Refractory cases require surgery. If a definitive lesion is demonstrated on MR then primary surgery can be undertaken.

The identification of MRI findings of quadrangular space syndrome and the exclusion of other treatable abnormalities in the shoulder may allow the institution of appropriate nonsurgical therapy to be followed potentially by surgical treatment in some refractory cases. Even if other shoulder abnormalities are present, findings of quadrangular space syndrome 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 quadrangular space syndrome on MRI by the usual involvement of more than one muscle or even more than one nerve distribution