Persistent median artery carpal tunnel syndrome : a case series and literature review

Section: Hand Abstract Persistent median artery (PMA) thrombosis is a rare cause of carpal tunnel syndrome (CTS) with only a few cases reported in the literature. The bifid median nerve (BMN) is often associated with PMA and may be a factor in the development of CTS. There is a paucity of information in the literature on the management options for CTS secondary to PMA thrombosis. This paper presents two cases of CTS with associated PMA thrombosis and BMN and offers a discussion on diagnostic and management options.


Embryology
The median artery is usually a transitory vessel that develops from the brachial axial artery in early embryonic life. 145][16] After the eighth week of gestation, the median artery usually regresses and the ulnar and radial arteries then dominate arterial supply of the hand. 14The vestigial median artery remains as the arteria comitans nervi median which accompanies the median nerve in to the forearm. 17It becomes perceived as a 'persistent median artery' when it is of a diameter and presence large enough to be noticed either through ultrasound or visual inspection. 18Persistent median artery has been described in two different patterns based on the vascular territory: palmar and antebrachial. 19In the palmar type, the PMA reaches the hand while in the antebrachial type, it terminates before reaching the wrist. 19When extending into the carpal tunnel, PMA may join the superficial volar arch, may supply the radial digits with an absent arch, or may end as a thrombosed vessel. 20In the majority of studies, PMA has been observed to be unilateral and assuming a position ulnar to the median nerve in the distal forearm. 20e median nerve is the only nerve to travel through the carpal tunnel.Anatomical variations of the median nerve are common and well-described in the literature. 21In 1977, Lanz classified median nerve anatomic variations into four groups, group III being the bifid or high division median nerve. 8e two parts of the nerve may be equal in size or a predominance may exist of either the radial or ulnar part. 22This may be clinically relevant in cases in which there is a pathology of the median vessels because the bifid nerve anomaly may be missed if the small ulnar division is surrounded by the abnormal median vessels. 7The most common variants of BMN are accompanied by persistent median vessels with or without involved pathology. 7

Persistent median artery, bifid median nerve and carpal tunnel syndrome
7][28][29] Thrombosis is the most frequently reported cause.[32][33] The mechanism by which PMA thrombosis produces CTS has been proposed to be either directly through nerve compression or by an ischaemic phenomenon from a poor anastomotic connection between the median, ulnar and radial arteries. 23,30,34Consistent with the cases in this study, PMA thrombosis symptoms usually include acute or sub-acute pain and parathesiae in the median nerve territory of the hand. 30ere is no consensus in the literature regarding BMN as an independent risk factor for CTS.In 2008, Bayrak et al proposed that BMN may predispose to median nerve compression and CTS because of a higher cross-sectional area relative to that of a nonbifid median nerve.However, a higher BMN crosssectional area was only found in the control group and not in the patient group. 3The study did find a significant difference in the relative frequency of BMN in CTS patients versus the control population. 3his is in contrast to the 2011 study by Granata et al who demonstrated, using ultrasonography, that the prevalence of BMN had a similar frequency in the patient group affected by CTS and in symptom free control group. 21dian nerve conduction studies are often considered the gold standard investigation in CTS diagnosis. 35Imaging studies such as ultrasonography and MRI are promoted with the claim they may reveal anatomical variants such as PMA and BMN that are responsible for some atypical CTS presentations.1][22] Both of the patients included in this study had Doppler ultrasonography prior to surgery for diagnosis of PMA thrombosis and BMN.It appears that only some of previous case studies reporting PMA thrombosis in CTS used ultrasonography for diagnosis prior to treatment, and in others the pathology was found at surgical exploration. 1,23,25,30,36,37Kele et al used preoperative ultrasonography in a single case of PMA thrombosis CTS. 33They state that ultrasonography was beneficial for diagnosis of the pathology and influenced the selection of surgical equipment and anaesthesia used. 33It was also argued that preoperative ultrasonography may reduce the risk of iatrogenic trauma.There are no studies that have compared outcomes in PMA thrombosis CTS in patients who have and have not had preoperative imaging.

Management
The limited number of case studies that describe PMA thrombosis with CTS show inconsistencies in management.Conservative management with anticoagulation versus surgical management is the first and most significant divergence in treatment.In 2012, Rzepecka-Wejs et al described a case of CTS with Doppler ultrasound proven PMA thrombosis that was managed with unspecified anticoagulant therapy and had nearly complete remission of symptoms over a three month follow up period. 38In 2015, Srivastava et al also described an acute carpal tunnel with ultrasound proven PMA thrombosis that was treated with therapeutic enoxaparin and warfarin and had marked improvement in symptoms after four weeks of anticoagulation. 39Resolution of CTS symptoms and re-canalisation of PMA thrombosis with unspecified therapeutic anticoagulation was also reported in the case report by Salter et al in 2011. 23Akgun and colleagues describe a case of CTS secondary to PMA thrombosis in an eight-week-pregnant woman where no treatment was undertaken by the patient because of the pregnancy, however, over the Nowicki, Cameron, Griffin et al: Persistent median artery carpal tunnel syndrome: a case series and literature review following weeks, the patient gradually became less symptomatic. 1It should be noted that these reports came from non-surgical specialties which may explain the preference for non-operative management.
In the two cases described here, the flexor retinaculum was released and the thrombosed PMA and BMN were left intact.The patients were not given anticoagulants.As far as we are aware, this is the first report to describe this surgical treatment for CTS secondary to PMA thrombosis.
Two case studies describe reports of CTS secondary to PMA thrombosis where the flexor retinaculum was released and additionally the thrombosed vessel excised. 25,30In the 2002 study by Khashaba et al the patient had ongoing numbness in the ring and index fingers for ten months postoperatively and had residual dysaesthesia over the radial aspect of the ring finger. 30Several studies have recommended that resection of the thrombosed PMA should generally be avoided because it involves the potential for vascular compromise in the hand. 2,26,39However, there are no reports in the literature that describe this occurring or that demonstrate a hand with full arterial dependence on the PMA.Arterial studies may be performed preoperatively to evaluate radial, ulnar arteries and PMA's contribution to the hand's circulation.

Conclusion
There are very limited studies reporting surgical management of BMN in CTS.Emphasis in reports is placed on preserving the median nerve branches while releasing the flexor retinaculum. 7,24 treating acute, severe carpal tunnel syndrome, we propose an open carpal tunnel release be performed and the nerve be inspected for the presence of an adjacent PMA.A thrombosed PMA can precipitate acute carpal tunnel syndrome with the consequent tissue inflammation causing an increase in carpal tunnel contents and subsequent provocation of pressure neuropathy.Previous experience of pressure neuropathy demonstrates that severity of nerve injury is a complex result of degree of ischaemia, duration of ischaemia and previous background injury together with patient medical factors.In the case of PMA thrombosis

AJOPS | CASE SERIES
within the carpal tunnel, the ischaemic insult to the nerve will be of a dual nature: the injury to the arborisation of the arterial vascularity of the median nerve will be major, while the extrinsic compression from the enveloping walls of the carpal tunnel on the swollen contents will supplement the injury.It is reasonable to release the carpal tunnel as soon as possible and decide under direct vision at that time whether microsurgical resection of the thrombosed section of the artery will benefit the recovering nerve.That assessment will depend upon the overall balance of tissue tensions and that individual arterial pattern.
We have experienced benefit with preoperative Doppler ultrasonography.This included both diagnosis of pathology and the preoperative planning.As a result of ultrasonography findings, endoscopic approaches were not considered, markings were made to include a more proximal incision, both patients were in a state of general anesthesia and a consultant surgeon was present for both operations.Lastly, despite there being no discussions in the literature regarding the rate of recurrence with conservative management, surgical treatment as above can be considered more definitive and therefore potentially associated with a lower rate of recurrence.

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limited in the literature.This review presents two cases of CTS with associated PMA thrombosis and BMN and offers a discussion on diagnostic and management options.Case year-old female with a past medical history of rheumatic heart disease presented with shooting pains in her right wrist and hand.Two weeks prior she had sustained a crush injury to her right wrist.Prior to her injury she had no symptoms in her wrist or hand.On examination she had reduced sensation in the median nerve distribution and had positive Phalen's and Tinel's tests.High resolution ultrasonography and Doppler demonstrated a BMN with PMA thrombosis (Figure 1).A segment of thrombus extending over a distance of 22 mm was noted at the wrist involving the PMA.The thrombosed segment was noted to be causing a mild mass effect on the adjacent bifid nerve bundles without change in nerve calibre.The distal artery demonstrated reconstituted flow.After discussion of treatment options, the patient underwent an open carpal tunnel release.The thrombosed, enlarged median artery was identified intraoperatively adjacent to, and overlying, the median nerve, causing compression within the carpal tunnel.The flexor retinaculum was released and the thrombosed segment of the artery was left intact (Figure 2).The patient was reviewed in the outpatient hand clinic one week later and reported relief of her symptoms.At follow-up 12 weeks post-surgery she reported having pillar pain and weakness when using her hand.Her pain and dysaesthesia was relieved through anti-inflammatories.The patient received no anticoagulation throughout their treatment.Case 59-year-old female presented with a six week history of progressively worsening pain and paraesthesia over the radial aspect of her right hand.She had sustained no injuries prior to the onset of her symptoms.Her past medical history comprised of idiopathic cardiomyopathy, hypertension, hyperlipidemia and heavy smoking.High-resolution Doppler ultrasound demonstrated

Fig 1 .Fig 2 .Fig 3 .
Fig 1. Case 1. High resolution ultrasonography visualizing bifid median nerve (circled structures A and B on left image, C and D on right image).The left image is immediately proximal to the flexor retinaculum and the right image is at the level of the proximal carpal bones.The right image demonstrates a thrombosed PMA in between the two trunks (C and D) of the bifid median nerve.PMA = persistent median artery BMN = bifid median nerve

Fig 5 .
Fig 5. Case 2 Intraoperative photograph after flexor retinaculum release demonstrating two trunks of a BMA and a thrombosed PMA coursing between the two nerve trunks.PMA = persistent median artery, BMN = bifid median nerve