A Solid Ulnar-Volar Wrist Mass After a Failed Aspiration
A 47-year-old woman presents with a slowly enlarging, mildly tender mass at the volar-ulnar aspect of the right wrist present for two years, with intermittent tingling of the small and ring fingers that is worse with wrist flexion. Tinel sign over the mass is positive and percussion reproduces pain radiating into the ulnar digits. There is no intrinsic wasting and grip strength is symmetric. Six months ago another provider aspirated the mass, obtained no fluid, and caused severe pain radiating into the hand. Ultrasound now shows a solid, well-defined hypoechoic mass measuring 2.5 cm in the region of Guyon canal, with internal vascularity on Doppler.
1. Give your differential diagnosis and your workup. What did the failed aspiration tell you, and would you biopsy the mass?
Read the worked answer
Differential:
- Ganglion cyst is the most common mass in this region, but it is usually cystic and anechoic rather than solid and vascular, and aspiration yields fluid.
- Peripheral nerve sheath tumor, most likely a schwannoma, is suggested by a solid mass in continuity with the ulnar nerve, a positive Tinel sign, and radiating pain on needling.
- Ulnar artery aneurysm, thrombosis, or hypothenar hammer syndrome should be considered for any pulsatile or ulnar-sided mass, particularly with repetitive palmar trauma.
- Giant cell tumor of tendon sheath, lipoma, fibroma, or an accessory abductor digiti minimi muscle are less likely given the imaging.
- Sarcoma is rare but must be on the list for any deep, solid, vascularized mass.
The failed aspiration is informative: no fluid argues against a simple ganglion, and the severe radiating pain argues that the needle entered a nerve-related structure. Needling a suspected nerve sheath tumor is painful and can injure fascicles. Do not repeat it, and do not perform an office biopsy.
Workup: contrast-enhanced MRI to define the relationship to the ulnar nerve and to look for the target sign and split-fat sign, and to distinguish an eccentric lesion (schwannoma) from a fusiform expansion of the nerve (neurofibroma). Plain radiographs for calcification. Refer to a hand surgeon with microsurgical capability rather than watchful waiting, given the progressive nerve symptoms.
2. MRI shows an eccentrically placed, well-defined mass with the ulnar nerve draped over its surface. Describe your operative plan and the principles behind it.
Read the worked answer
Plan: through a volar-ulnar incision, identify the ulnar nerve proximally in normal tissue and trace it distally, using the operating microscope and a tourniquet. Decompress Guyon canal and mobilize the nerve sufficiently to work without traction.
Principle: enucleate, do not resect. Schwannomas displace fascicles rather than infiltrating them. Open the epineurium longitudinally over the tumor and shell the mass out, preserving the fascicles that run over its surface; send the specimen for frozen section if the diagnosis is in question. Stimulate the nerve after excision to confirm continuity. Do not sacrifice a functioning fascicle for a benign tumor, and do not attempt a marginal resection en bloc.
Consent: partial resection if the tumor proves not to be a schwannoma; temporary or permanent sensory deficit in the ulnar distribution; neuroma; recurrence; and the possibility that a second operation will be needed if final pathology changes the diagnosis.
If it proves to be a neurofibroma (fusiform, nerve expanded, fascicles entering and leaving the mass), enucleation is not possible. If the deficit is mild, closing and observing is often better than resection. If there is progressive motor or sensory loss, resection with interpositional nerve grafting, or a distal sensory transfer, is the alternative. Never resect a neurofibroma without a reconstruction plan in hand.
3. Final pathology returns a malignant peripheral nerve sheath tumor. What are the next steps, including surveillance and counseling?
Read the worked answer
Staging and referral: MRI with contrast of the entire compartment, chest imaging or PET-CT, and referral to a sarcoma center. A mass enucleated under the assumption of benign disease almost certainly has positive margins; the patient needs re-excision to obtain wide, negative margins, usually combined with radiation. Explain plainly that the first operation was appropriate for the presumed diagnosis but is not definitive treatment, so that the recommendation for further surgery is not heard as a mistake.
Syndromic association: malignant peripheral nerve sheath tumors are associated with neurofibromatosis type 1. Examine for cafe-au-lait macules, axillary freckling, and cutaneous neurofibromas, take a family history, and refer for genetic counseling if any features are present.
Counseling and surveillance: discuss the guarded prognosis of these tumors honestly, the possibility of adjuvant therapy, and the functional consequences of wider resection, which may include ulnar nerve sacrifice and the need for tendon transfers or nerve reconstruction. Arrange clinical review and imaging every three to six months for the first two to three years, then annually, and instruct her to report new pain, rapid growth, or a change in the mass. If the final diagnosis had instead been a benign schwannoma after complete enucleation, recurrence is uncommon and routine imaging is not needed unless symptoms return.