Case Report: Presentation of an unusual cause of carpal tunnel syndrome with accompanying literature review

Introduction

Carpal tunnel syndrome (CTS) is a condition commonly encountered by physicians and surgeons alike, with the prevalence in the general population ranging from 3–5%¹ and accounting for up to 90% of all entrapment neuropathies². The finding of a congenital arteriovenous malformation (AVM) is a much less common occurrence in clinical practice, with some studies suggesting a prevalence of 1 in 100,000, with the majority of these occurring in the head and neck, with peripheral limb AVMs rarer still³. AVMs have a tendency to grow progressively larger with age, only becoming symptomatic when associated with haemodynamic instability or compression of surrounding structures⁴.

Case report

Our patient was a 58-year-old man who had migrated to Australia from South Sudan. He was left hand dominant with no known medical comorbidities or past surgical history. He had been referred to our general surgical outpatients clinic by his general practitioner with a nerve conduction test that had confirmed the presence of a severe left sided CTS.

The patient provided us with a 12 month history of transient paraesthesia in the distribution of the median nerve with sparing of the palmar cutaneous region. He reported that his left hand had been pulsatile his whole life and despite being ungainly was, until recently, asymptomatic. On inspection, his symptomatic left hand was 50% larger in comparison to his right. On palpation, thrills were appreciated in association with the multiple aneurysmal bulges. We hypothesised that an AVM was present deep to the flexor retinaculum and had caused some degree of compression to the median nerve. We subsequently arranged for him to undergo CT angiography, which confirmed our suspicions. (Figure 1)

Figure 1. Coronal and sagittal views on CT angiography pre-embolisation.

In an attempt to relieve his symptoms we arranged for the patient to undergo angiography with endovascular embolisation. Multiple large aneurysmal sacs were coiled and feeding vessels embolised; however, the extent of the abnormal vasculature in this instance was considerable and definitive treatment was unable to be established without incurring a significant risk of ischaemia to the patient’s hand.

Immediately post-intervention, the patient did not report any difference in his symptoms and this remained to be the case until 6 months post-procedure. At this visit it was observed that his AVM had significantly reduced in size macroscopically and the patient reported improvement in his symptoms. This change correlated with a volumetric reduction on repeat CT angiogram; it was postulated that this could be attributed to a delayed fibrosis following embolisation (Figure 2).

Figure 2. Coronal and sagittal views on CT angiography 6 months post-embolisation.

Unfortunately, this improvement was only transient and at 9 months post procedure his AVM had again spontaneously reverted to its original pre-intervention dimensions.

The patient’s case was subsequently discussed at several multidisciplinary meetings, eventually a high-risk surgical procedure involving resection of the AVM with multiple vascular graft reconstruction was offered to the patient. However, he ultimately decided to continue living with his symptoms rather than risk compromising his hand function or viability.

Discussion

Direct compression of the median nerve by a congenital AVM within the flexor retinaculum is a particularly unlikely cause of carpal tunnel syndrome, made even more remarkable by the fact that the patient in this case only became symptomatic in the fifth decade of life.

Low-flow AVMs may be clinically less concerning as they are more amenable to surgical or endovascular intervention and appear to have lower rates of recurrence when compared to high-flow AVMs.

Most AVMs involing the extremities feature low-resistance niduses between the arteries and veins. Rosen and colleagues suggest that in the management of high-flow vascular malformations if these niduses are not adequately controlled, then attempts at embolising or coiling of the proximal feeding vessels are likely to fail as new collateral feeders will invariably develop to replace them¹³, such as was the experience with our patient.

Conclusion

Peripheral limb high-flow AVM can be a rare and therapeutically challenging cause of carpal tunnel syndrome. It is a complex issue which warrants multidisciplinary team discussion, as complications of treatment and recurrence must be carefully weighed against the likelihood of improvement on a case-by-case basis.

Consent

Formal written consent for publication was obtained from the patient prior to the writing of the case report.

Data availability

All data underlying the results are available as part of the article and no additional source data are required.