An intraneural ganglion cyst of the dorsal cutaneous branch of the ulnar nerve arising from the wrist: support for the articular origin. Illustrative case

Abstract

BACKGROUND

The articular theory of the formation of intraneural cysts has significant supporting evidence at common locations but has been less accepted at rarer sites. There have been only 5 cases in the literature documenting an intraneural ganglion cyst in the dorsal cutaneous branch of the ulnar nerve (DCBUN), with only 1 case documenting a joint connection. In this report, the authors present a second case with a proven joint connection in support of the articular theory.

OBSERVATIONS

The authors report the case of a 73-year-old man who developed a large intraneural ganglion cyst within the DCBUN along the palmar ulnar aspect of his left wrist. Magnetic resonance imaging demonstrated an articular connection to the distal radioulnar joint. During surgery, the intraneural ganglion cyst was resected and the articular branch was disconnected. The patient recovered and returned to work 4 weeks postoperatively.

LESSONS

This case further supports the articular theory as the explanation for intraneural ganglion cysts, even at unusual locations.

https://thejns.org/doi/10.3171/CASE24569

Intraneural ganglion cysts are mucinous, nonneoplastic cysts that are found within the epineurium of peripheral nerves. While their origin has been controversial, an increasing large body of literature supports the articular (synovial) theory as the accepted etiology of intraneural ganglion cyst formation: a capsular rent occurs within a joint capsule and joint fluid egresses along an articular branch of a nerve, following the path of least resistance toward the parent nerve, dependent on pressures.¹, ² While this theory was originally established and subsequently corroborated at the most common site of intraneural ganglion cyst formation—the common peroneal nerve at the fibular neck arising from the superior tibiofibular joint—it has not been adequately tested, substantiated, and accepted at rarer locations.^3–6 A 2016 systematic review of the literature documented several sites where there had not been any documented cases of intraneural ganglion cysts with joint connections, including the superficial radial nerve and the dorsal cutaneous branch of the ulnar nerve (DCBUN).⁶ Since that review, our group has provided evidence to support a joint connection to the wrist for intraneural ganglion cysts of the superficial radial nerve.² In this report, we present the case of a patient with an intraneural ganglion cyst of the DCBUN with a proven connection between the cyst and the distal radioulnar joint (DRUJ), with cyst involving the triangular fibrocartilage complex (TFCC) to support that intraneural ganglion cysts in rare locations follow the same principles of formation as those in more common locations.

Illustrative Case

A 73-year-old man presented with a 2-month history of a large cystic lesion along the palmar ulnar aspect of his left wrist. The mass would increase and diminish in size. The patient had no neurological symptoms, and there was no history of an antecedent traumatic event. He had a fluctuant, transilluminating mass approximately 5.5 cm in length and 2 cm in width. It was nontender to palpation. Neurological examination was normal, including 2-point discrimination in all digits. He had a full, pain-free range of motion in the wrist and forearm.

Radiographs showed moderate osteoarthritis of the first carpometacarpal and scaphotrapeziotrapezoid joints and osteophytosis of the ulnar styloid process. At the ventral aspect of the distal arm, there was an exophytic soft tissue lesion. Magnetic resonance imaging (MRI) demonstrated a large, multilobulated fluid-filled cystic structure consistent with a ganglion arising from the ulnocarpal area (Fig. 1). A multilocular cystic mass measuring 2.6 cm (mediolateral) × 1.2 cm (anteroposterior) × 6 cm (superoinferior) was noted that was centered in the subcutaneous compartment of the volar and ulnar distal forearm through the wrist. Postcontrast imaging demonstrated no solid components. A connection with the ulnar side of the wrist joint was demonstrated. There was a complex peripheral tear of the TFCC with extension into the fovea, associated with a small adjacent extraneural ganglion cyst. A communicating defect through the TFCC disc to the DRUJ was apparent. There was mild tendinosis of the extensor carpi ulnaris and tenosynovitis and high-grade cartilage loss of the ulnar head.

FIG. 1.

A: Coronal T2-weighted MRI scan of the volar wrist with fat suppression, showing the multiloculated cyst (asterisks) along the ulnar wrist with a joint connection to the distal radioulnar joint (DRUJ) (not shown). B: Coronal T1-weighted MRI scan with fat suppression at a level of 1 following contrast administration, showing the nonenhancing ganglion with a thin enhancing margin (asterisks). C: Sagittal T2-weighted MRI scan with fat suppression of the wrist, showing the joint connection (arrowheads) to the DRUJ. The cyst (asterisks) is oriented along the course of the DCBUN. D: Axial T2-weighted MRI scan with fat suppression at the level of the radiocarpal joint, showing the cyst (asterisk) at the volar ulnar wrist in the expected location of the DCBUN. The arrow indicates the extensor carpi ulnaris tendon, which is thickened with intrasubstance tearing. P = pisiform; R = radius; U = ulnar head.

Treatment options discussed for this presumed joint-connected extraneural ganglion cyst included nonoperative care, as the swelling was not particularly bothersome; aspiration, which would be unlikely to eradicate the cyst; and surgery, with a 10% risk of recurrence. The patient elected to proceed with surgery, which was performed as an outpatient procedure under axillary block anesthetic and intravenous sedation with excision of the left wrist ganglion. A palmar ulnar zigzag-pattern incision was used, which began just proximal to the balloon-like expansion of the cyst and extended to the wrist. The ulnar neurovascular bundle was visualized and found to lie well below the level of the cyst. The point of origin of the DCBUN was then identified and controlled. An intraneural ganglion cyst involving the DCBUN was identified. The main ulnar nerve was not involved by the ganglion (Fig. 2A and B). Skin flaps were elevated carefully from the underlying cyst. The cyst wall was very thin and somewhat adherent to the skin. Skin flaps were elevated without difficulty. The cyst tracked along the DCBUN, which was separated from the ganglion (Fig. 2C). The pedicle of the cyst was disconnected near the wrist. The cyst was resected without any leakage of mucinous material from the ulnar palmar aspect of the forearm. The specimen was sent to pathology (Fig. 2D), which confirmed the diagnosis of a ganglion. The tourniquet was released, and hemostasis was obtained. The skin was closed in layers, and a bulky postoperative dressing with a volar splint was applied. Postoperatively, the patient did well. At the 6-week follow-up, he had no complaints, retained his muscle strength and sensation, and had returned to work as a handyman.

FIG. 2.

A: The cyst (asterisk) is demonstrated in the ulnar aspect of the volar distal forearm. B: The ulnar nerve is seen, as is the DCBUN (in blue vessel loops). The intraneural cyst (asterisk) has been teased away from proximal (Prox) to distal (Dist) where it headed toward the DRUJ. C: The cyst (asterisk) has been resected. D: The underlying ulnar nerve and DCBUN (on background) have been preserved.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Intraneural ganglion cysts in the wrist region are rare. Of 1000 cases of intraneural cysts in our database of the world’s literature, only 71 occurred in the wrist. These include the following specific nerves: ulnar (n = 24), deep branch of the ulnar nerve (n = 17), superficial radial (n = 12), median (n = 8), DCBUN (n = 5), lateral antebrachial cutaneous (n = 1), palmar cutaneous branch of the median nerve (n = 1), posterior antebrachial cutaneous (n = 1), posterior interosseous (n = 1), superficial branch of the ulnar nerve (n = 1), and deep and superficial branches of the ulnar nerve (n = 1) (Fig. 3A). The articular theory at the wrist can be supported by historical information dating back to 1884: surgeons F. Swinford Edwards and Anthony Bowlby identified the first described intraneural ganglion cyst in a cadaveric specimen (a deep ulnar intraneural cyst with a carpal joint connection).^{7, 8} While this report focuses on intraneural ganglion cysts, extraneural ganglion cysts at the wrist are more common and are well known to form from neighboring joints. In a recent literature review on wrist ganglia, 91% were found to be extraneural compared to only 9% that were intraneural.⁹ Extraneural ganglion cysts can occasionally compress the DCBUN and result in similar symptoms to those of intraneural cysts.¹⁰ Other major causes of DCBUN neuropathy include direct trauma and procedures in the distal arm/wrist, including extraneural ganglion excision.¹¹

FIG. 3.

Intraneural wrist cysts. A:Composite of all published intraneural ganglion cysts at the wrist/palm level. The numbers are based on our prospectively maintained database of all published cases and have been updated since the paper by Desy et al.⁶ All cases could well be explained based on the articular theory. B and C:Examples of a DCBUN intraneural cyst arising from the TFCC (B) yet to be described and DRUJ (C; communicating with cyst in the TFCC) to reflect our case and the case of Naam et al.¹³ Based on the anatomy depicted, one could also explain the remaining cases (not drawn).^12–15

During our literature review, we found only 4 publications documenting a total of 5 cases of intraneural ganglion cysts affecting the DCBUN (Table 1).^12–15 This includes the 3 found in the systematic review by Desy et al.,⁶ which included the publication by Dubs¹² in 1922 of a posttraumatic case: these 3 cases did not identify a joint connection to the wrist. Two cases were published by Naam et al.¹³ (part of a 15-patient study) subsequent to the inclusion time for the systematic review, 1 of which had a joint connection. All these cases underwent successful operations with no reported recurrences.

TABLE 1.

Literature review of cases of intraneural ganglion cysts in the DCBUN

Authors & Year	Gender	Age (yrs)	Trauma	Joint Connection Identified	MRI	Surgery	Outcome
Dubs, 192212	M	68	Yes	No	No	Resection	Pain relief, weakness decreased
Giele & Le Viet, 199715	M	45	No	No	No	Resection	Full recovery
Patel et al., 199714	M	36	No	No	No	Incision & evacuation	Complete sensation return in 1 wk
Naam et al., 201513	UK	UK	No	No	Yes	Incision & evacuation of articular branch	Full recovery
Naam et al., 201513	UK	UK	No	Yes, distal radioulnar	Yes	Resection	Full recovery

UK = unknown.

While only 1 of the 5 previous reports had an associated articular nerve connection identified, we believe that the other 4 cases did not identify the joint connections. This suggests that intraneural ganglion cysts in the DCBUN do not present a rare exception to the articular theory. Previously, our group has shown that, by retrospective review of published MRI studies, unrecognized joint connections of intraneural ganglion cysts can be identified at many different sites, including the wrist.⁶, ¹⁶, ¹⁷ The majority of the previous cases did not use MRI.^12–15 High-resolution MRI has proven valuable in identification of the joint connection, which suggests a higher likelihood that these were missed previously but can now be identified.^18–20 Additionally, examination of the locations of the cysts documented suggests a synovial origin. One was reported at the base of the 5th metacarpal, making it very likely that the 5th carpal-metacarpal joint was involved.¹³, ²¹ The location described by Dubs,¹² somewhat proximal to the point where the branches to the 4th and 5th fingers depart, is where a cyst originating from the ulnocarpal joint or the TFCC would be suspected (Fig. 3B). Similar to our case, the cyst with an identified articular nerve connection was found at the level of the DRUJ, with that joint being involved (Fig. 3C).¹³ Finally, while Patel et al.¹⁴ did not specify the location of the cyst beyond the “ulnar side of his right wrist,” the image they provided shows the cyst in a location similar to that found in this report.

The DCBUN, in addition to providing sensation in the ulnar distribution through the hand/fingers, innervates 4 of the joints of the wrist; branching off the ulnar nerve 5 cm proximal to the ulnar styloid process, it innervates the ulnocarpal joint including the TFCC, the 4th and 5th carpometacarpal joints, and the DRUJ.^21–25 According to the articular theory of intraneural ganglion formation, pathology in any of these 4 joints could result in an intraneural ganglion cyst arising in the DCBUN, with a very small synovial connection to the joint of origin.¹, ², ⁴, ¹⁷, ²⁶ Recognizing the articular connection, for intraneural cysts in the DCBUN as well as any other nerve, is important because surgical management requires severing the connection in order to prevent intraneural cyst recurrence or persistence.²⁷ It should be noted that definitive documentation of recurrence requires postoperative evaluation of MRI performed months after surgery, which is very rarely done.

The innervation of the wrist joints is complex, with 9 nerves providing overlapping innervation to the joint—4 anteriorly and 5 dorsally.²¹ The wrist joints have also been documented to be innervated by the medial antebrachial cutaneous nerve, posterior interosseous nerve, volar branch of the ulnar nerve, palmar cutaneous branch of the median nerve, and the anterior interosseous nerve.²⁴, ^28–32 For joints innervated by only 1 nerve, severing the articular connection between the cyst and the joint should not result in intraneural recurrence.¹³, ²⁷ However, when many nerves innervate the same joint, a pattern of recurrence could emerge where an untreated pathological joint causes an intraneural cyst in one of the remaining connecting nerves.²⁷ While rare, these types of intraneural recurrences have been reported in the literature.³³, ³⁴ In addition to the DCBUN intraneural cysts, multiple other nerves at the wrist have joint-originating intraneural cysts documented, including the median, ulnar, ulnar deep motor branch, superficial radial, and posterior interosseous;², ⁶, ³⁵ there have been two ulnar intraneural ganglion cysts arising from the DRUJ^{36, 37} and one from the ulnocarpal joint.³⁸

Knowledge of the articular anatomy of the wrist is important and has implications clinically regarding pain procedures, particularly denervation of the wrist. A common technique is a complete denervation, called “Wilhelm’s³⁹ denervation procedure,” which severs the connection between the joint and each nerve supplying it.²¹,^40–42 Some have also attempted partial denervation. Recently, the DCBUN has been identified as a target for ulnar-sided wrist denervation.⁴³

Lessons

We believe that the unified articular theory explains all cases of intraneural ganglion cyst formation, including those at the wrist and in the DCBUN.⁴⁴ While other theories for the formation of intraneural ganglion cysts have been put forth over the past 2 centuries, they have not been substantiated; ultimately, we do not believe that there are privileged sites where the articular theory does not apply. This paper further supports the articular theory as an explanation for intraneural ganglion cysts, even at unusual locations. It is the second paper to report a joint connection of an intraneural cyst in the DCBUN to the DRUJ and the first paper to publish MRI data as definitive proof of an articular-cystic connection.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Spinner, Amrami. Acquisition of data: Spinner, Amrami, Bishop. Analysis and interpretation of data: Spinner, O’Driscoll, Amrami. Drafting the article: Spinner, O’Driscoll, Amrami. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Spinner. Statistical analysis: O’Driscoll. Administrative/technical/material support: Spinner, O’Driscoll. Study supervision: Spinner. Conducted literature review: O’Driscoll.

Correspondence

Robert J. Spinner: Mayo Clinic, Rochester, MN. spinner.robert@mayo.edu.