Compressive ulnar neuropathy owing to a tortuous ulnar artery proximal to Guyon’s canal

A 49-year-old woman presented with an 18-month history of progressive tingling and paresthesia in the hypothenar area of her right hand. She had no history of any chronic disease or previous wrist trauma. On examination, a positive Tinel’s sign over the ulnar nerve was elicited 3 cm proximal to the palmar wrist crease with decreased sensation to touch and pinprick stimuli over the hypothenar eminence. No palpable swellings were detected and there was no wasting of the hypothenar or interossei muscles with normal strength compared with the other hand.

Radiographs of the right hand and wrist were normal. Nerve conduction studies showed normal motor nerve latency, amplitude and conduction velocity but diminished sensory nerve action potential in the dorsal sensory branch of the right ulnar nerve. An MRI scan showed a focal C-curved deviation of the ulnar nerve by a tortuous ulnar artery 3 cm proximal to Guyon’s canal with mild ulnar nerve oedema (Figure 1).

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Figure 1.

Fat-suppressed T₂-weighted MRI scans show the mildly oedematous tortuous ulnar artery compressing the ulnar nerve on the radial side (white arrow).

Surgery was carried out to confirm and treat the suspected compressive lesion. A 5 cm longitudinal incision was made over the positive Tinel point, radial to the flexor carpi ulnaris tendon. A tortuous ulnar artery was found compressing and deviating the ulnar nerve ulnarly (Figure 2(a)). The nerve was oedematous, strongly suggestive of a peripheral compressive neuropathy (Elhassan and Steinmann, 2007) (Figure 2(b)). Neurolysis was carried out and the artery was repositioned radially. A small radial-based fat pedicle sling was harvested to fix the ulnar artery to the adjacent fascia (Figure 2(c)). Guyon's canal was not explored as the compression was proximal to the canal.

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Figure 2.

(a) Surgery showing the tortuous ulnar artery compressing the ulnar nerve; (b) after neurolysis, the ulnar nerve is shown to be indented and swollen and (c) the mobilized ulnar artery is fixed to the adjacent fascia using the fat sling (white dot line).

After surgery, most of her paresthesia was relieved and at the 2 year follow-up; her persistent all-day symptoms had subsided to only mild, occasional paresthesia. She preferred not to have repeat nerve conduction studies carried out.

Natroshvili et al. (2024) proposed that ganglia, lipomas, cysts, ligament or muscle abnormalities, ulnar artery aneurysms, bone fractures and repetitive trauma were the most common causes of compression in the narrow space of Guyon’s canal. Proximal to the wrist, the ulnar artery follows a slightly tortuous path separate from the nerve before it enters Guyon’s canal and they come together as they pass under the hypothenar muscle and flexor retinaculum (Yamamoto et al., 2021). A tortuous ulnar artery can also compress the nerve within the canal (Jose et al., 2006). Compression of the nerve proximal to Guyon’s canal from a tortuous artery is rare, but when the clinical signs suggest this possibility, nerve conduction studies and MRI are useful diagnostic investigations.