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Neuroradiology Case of
the Week
Case 216
Igor Mikityansky, MD, MPH
Clinical
Presentation:
A 40-year-old male with proximal right upper extremity weakness on physical exam after a gunfight. The patient had an oblique bullet track in the right trapezium muscle above the trunks and roots, thus not causing patient's symptoms. Injury to the trachea and subsequent tracheostomy prevented further elucidation of symptoms.
Radiological Findings: An irregular 2 x 1.8 x 1.9 cm ovoid high attenuation density posteromedially to the junction between the proximal humeral diaphysis and metaphysis. The signal intensity is similar to the intravascular contrast. The density connects to the posterior circumflex artery of the arm.
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Figure 1A-C: The contrast enhanced CT demonstrates a irregular extravascular contrast collection posterior medially to the proximal humeral diaphysis, connected to the posterior circumflex artery of the arm.
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Figure 2: Diagram of the shoulder from posterior depicting quadrilateral space borders: Teres minor (Tm), Teres major (TM), Triceps (Tri), and Humerus (H). The Axillary nerve (arrow) and posterior humeral circumflex artery(arrowhead) pass through the quadrilateral space. Also depicted Infraspinatus (Is) and Supraspinatus (Ss) muscles. [5]
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Figure 3: Axial arteriogram demonstrates a focal well delineated collection of extravascular contrast consistent with pseudoaneurysm of the posterior circumflex artery of the right arm.
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Figure 4: The catheter selection of the posterior circumflex artery at the origin of the pseudoaneurysm.
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Figure 5: Contrast injection confirming catheter placement at the base of the pseudoaneurysm.
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Figure 6: Coil embolization of the pseudoaneurysm.
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Figure 7: Absence of the contrast filling confirming successful embolization of the pseudoaneurysm without occlusion of the distal segment of the posterior circumflex artery. |
Diagnosis: Pseudoaneurysm of the posterior circumflex artery of the arm in the quadrilateral space with axial nerve compression
Discussion: Upper extremity arterial aneurysms represent 2% of peripheral arterial aneurysms [1]. Aneurysms of the branches of the axillary artery below the pectoralis minor muscle are most commonly described in overhead throwing athletes, such as baseball and volleyball players, potentially due to hypertrophy of the humeral head and pectoralis muscles [2]. The posterior circumflex humeral artery (PCHA) is the most commonly reported location of the pseudoaneurysms. It supplies shoulder joint, deltoid, teres minor and major muscles, as well as long and lateral heads of triceps [3]. The mechanism of injury has been ascribed to repetitive injury of the artery by the humeral head or pectoralis minor muscle compression and shearing or tethering of the vascular ring of anterior and posterior circumflex arteries during hyperabduction and external rotation [2, 3]. Alternatively, tethering of the PCHA in the quadrilateral space on hyperabduction has been hypothesized to cause stretching of this artery at the origin and formation of the aneurysm. The quadrilateral space is located posterior medially to the humeral neck with humeral neck as a lateral and long head of the triceps as a medial boundaries, with teres minor and major muscles as superior and inferior ones, respectively (Figure 4) [2].
While initially asymptomatic, the clinical presentation of the aneurysm is related to arterial thrombosis or distal embolization [2, 3]. Patient present with claudication, inability to tolerate cold, hypersensitivity, pain in fingers, numbness and blanching [2]. The clinical differential includes thoracic outlet syndrome with poststenotic dilatation, valvular heart disease and arrhythmias, Raynauld’s disease, vasculitis, arterial thrombosis and distal aneurysms [2]. Therefore, physical examination echo and electrocardiograms are usually performed. The Doppler ultrasound, EMGs, nerve-conduction studies and photoplethysmography of the digits are also frequently part of the work-up of symptomatic patients [2]. The chest radiographs and angiography are performed to exclude presence of the cervical ribs and to define arterial anatomy and find the source of emboli [2]. The computerized tomographic or magnetic resonance arteriography with three-dimensional reconstructions can be used in preparation for surgical intervention [3].
In the symptomatic patients prompt treatment is needed to avoid gangrene of fingers or rupture of the aneurysm. Small aneurysms have been traditionally managed with excision and primary anastomosis, while large ones are managed with placement of saphenous vein or less-preferable synthetic grafts after resection [2]. Some surgeons advocate pectoralis minor muscle release if it appears to cause compression [2]. Embolization of the aneurysm has been recently used as an alternative to the surgical resection to prevent distal embolization [3].
The aneurysms of the axillary artery branches need to be distinguished from the quadrilateral space syndrome (QSS), which was described by Cahill and Palmer in 1980 [2]. Unlike the aneurysms that occur proximally to the quadrilateral space at the origin of the posterior circumflex artery, the pathogenesis of the QSS is related to the occlusion of the PCHA by a fibrous band or hypertrophied muscles in the QSS itself [4]. The less common causes of compression are ganglion, glenoid labral cyst, and a paralabral cyst. The axillary nerve is commonly compressed as well [4]. This syndrome is usually associated with quadrilateral space tenderness, neck and shoulder pain, deltoid and teres minor atrophy and weakness [4]. The EMG findings are usually not specific [4]. The arteriography demonstrating compression of the PHCA in the abducted and externally rotated arm has been used for the diagnosis of the syndrome. However, up to 80% of normal controls have positive findings [4]. On the other hand, MRI demonstrating selective teres minor atrophy has been reported to be specific for the QSS [4].
Initially QSS is managed conservatively with analgesics, physiotherapy and rest. While some advocate surgical decompression from the posterior approach to be performed immediately after diagnosis, in most cases it is performed after the failure of conservative management [4].
In our patient, the presentation was more typical for the axial nerve involvement as proximal upper extremity weakness was the reason for work-up rather than distal embolic symptoms typically described with symptomatic PCHA aneurysm. Most likely incidentally found distal PCHA pseudoaneurysm adjacent to the humeral neck in the quadrilateral space was atypical as well, since classic aneurysms are usually seen at the origin of this artery. Therefore, it is possible that in this case the pseudoaneurysm was compressing the nerve in the quadrilateral space, which resulted in the acute innervation compromise of the deltoid and teres minor muscles. The alternative explanation of patients symptoms is direct axillary nerve injury. The pseudoaneurysm was embolized to prevent complications and patient was referred to neurology for further evaluation of etiology of his complaints.
References:
- Kaufman JA, Lee MJ. Vascular & Interventional Radiology. Philadelphia, PA: Mosby; 2004.
- Schneider K, Kasparyan NG, Altchek DW, Fantini GA, Weiland AJ. An aneurysm involving the axillary artery and its branch vessels in a major league baseball pitcher. A case report and review of the literature. Am J Sports Med. May-Jun 1999;27(3):370-375. [Medline]
- Vlychou M, Spanomichos G, Chatziioannou A, Georganas M, Zavras GM. Embolisation of a traumatic aneurysm of the posterior circumflex humeral artery in a volleyball player. Br J Sports Med. Apr 2001;35(2):136-137. [Medline]
- Hoskins W., Pollard HP,McDonald AJ, Quadrilateral space syndrome: a case study and review of the literature. Br J Sports Med, 2005. 39(2): e9. [Medline]
- Stadnick ME. MRI web clinic. http://www.radsource.us/rf/RADS/Internal.aspx?PID=391.
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