Phantom limb pain, traumatic neuroma, or nerve sheath tumor? Illustrative case

Abstract

BACKGROUND

Phantom limb pain and traumatic neuromas are not commonly seen in neurosurgical practice. These conditions can present with similar symptoms; however, management of traumatic neuroma is often surgical, whereas phantom limb pain is treated with conservative measures.

OBSERVATIONS

A 77-year-old female patient with a long-standing history of an above-the-knee amputation experienced severe pain in her right posterior buttocks area for several years’ duration, attributed to phantom limb pain, which radiated down the stump of her leg and was treated with a variety of conservative measures. A recent exacerbation of her pain led to a prolonged hospitalization with magnetic resonance imaging of her leg stump, revealing a mass in the sciatic notch, at a relative distance from the stump. The anatomical location of the mass on the sciatic nerve in the notch led to a presumed radiological diagnosis of nerve sheath tumor, for which she underwent excision. At surgery, a neuroma of the proximal portion of the transected sciatic nerve that had retracted from the amputated stump to the notch was diagnosed.

LESSONS

Traumatic neuromas of transected major nerves after limb amputation should be considered in the differential diagnosis of phantom limb pain.

Traumatic neuromas are benign tumors that can occur after operations, including amputation.¹ They have unique considerations because there is no consensus treatment when seen in neurosurgical practice.² Through a careful patient history and histopathological analysis, these neuromas are subtly distinguished from other peripheral nerve tumors, such as schwannomas, given their similar symptomatic clinical presentation. They must also be carefully differentiated from phantom limb phenomenon when presenting in a patient with a limb amputation. Treatment options are debated when assessing a patient with a stump neuroma and can vary from a combination of drug therapies to resection.³

Here, we discuss a case of a patient with a 24-year history of a unilateral above-the-knee amputation and long-standing leg pain attributed to phantom limb phenomenon. However, recent imaging showed a mass in the sciatic nerve at the notch, initially thought to be a nerve sheath tumor. Exploration revealed instead a traumatic neuroma of the amputated proximal sciatic nerve stump that had retracted from the above-the-knee amputated stump all the way to the sciatic notch. This case description is used as an opportunity to broaden the neurosurgical recognition that traumatic neuromas of amputated nerves should be considered in the differential diagnosis of phantom limb pain.

Illustrative Case

History and Physical Examination

A 77-year-old woman underwent an above-the-knee amputation on her right side 24 years ago. A few years later, she began to experience disabling pain in the right stump, attributed to phantom limb pain. She was treated with several regimens of narcotics and nonnarcotics administered both orally and by injection. A recent exacerbation of pain radiation down the stump led to a prolonged hospitalization for pain control. On physical examination, the pain was worse when sitting, supine, and with palpation. A Tinel’s sign was difficult to interpret because of exquisite pain throughout the stump upon palpation that mimicked the phantom limb pain. The patient could ambulate by donning a prosthesis while using a cane or walker but mostly used a wheelchair. Magnetic resonance imaging (MRI) of her spine and pelvis was performed. Although the spine MRI did not provide an explanation for her pain, the pelvis MRI showed a well-defined gadolinium-enhancing lesion of the right sciatic nerve at the notch, directly below the piriformis muscle and deep to the right gluteus maximus (Fig. 1A and B).

FIG. 1.

Preoperative axial (A) and coronal (B) T1-weighted MRI with gadolinium contrast showing a mass measuring approximately 26.4 × 16.7 mm. Blue arrows indicate the mass in the sciatic notch, and the yellow arrow indicates the proximal sciatic nerve.

Surgical Findings

On the basis of the radiological impression of nerve sheath tumor, an excision was planned. Intraoperatively, the tumor was localized via ultrasound-guided Kopan needle wire localization (Fig. 2). This allowed a less invasive transgluteal approach, following the wire to the sciatic nerve mass emerging from the sciatic notch. A mass in the proximal nerve stump was visualized without a distal nerve, consistent with a traumatic neuroma and not a nerve sheath tumor (Fig. 3). This was confirmed by biopsy and pathological analysis. After excision of the mass, the proximal sciatic nerve stump was tightly ligated with sutures to prevent formation of a subsequent traumatic neuroma. The patient was discharged after a 5-day stay in the hospital. Postoperative MRI showed normal postsurgical changes and trace fluid within the resection bed. No residual lesion was seen on the postoperative MRI (Fig. 4).

FIG. 2.

Intraoperative gluteal ultrasound images (A and B) displaying a hypoechoic mass.

FIG. 3.

Photograph of the gross mass in the proximal nerve stump.

FIG. 4.

Axial (A) and coronal (B) postoperative T1-weighted MRI displayed the area with no residual mass visible.

Pathological Analysis

The gross specimen consisted of a tan-white-pink, rubbery, shaggy tissue fragment measuring 2.6 cm in its greatest dimension. The specimen was serially sectioned and exhibited a homogeneous appearance throughout. On microscopic examination, a well-organized nerve structure, likely representing branches of the sciatic nerve remnant, was identified and juxtaposed by a disorganized proliferation of nerve fibers with intervening collagen (Fig. 5).

FIG. 5.

Hematoxylin and eosin staining of the resected lesion displaying nerve fibers with intervening collagen, findings consistent with the pathological diagnosis of a traumatic neuroma.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

Phantom limb pain consists of pain, pruritus, paresthesia, or hot and cold sensations that occur after the amputation of a limb.⁴ First-line treatment options are pharmacological.⁵ Patients who do not respond to pharmacotherapy can be offered sensory motor training, mirror therapy, and noninvasive neuromodulation.⁵ Unfortunately, there is a high rate of treatment failure.

The lesson in this case would be to consider other factors contributing to pain that had been present over 20 years. The MRI, surgical, and pathological findings ultimately showed that a neuroma had formed in the proximal stump of the sciatic nerve. This proximal amputated segment of the nerve must have retracted from the above-the-knee amputated region all the way to the sciatic notch. In fact, an initial radiological impression that the mass was a nerve sheath tumor did not consider the unlikely event that the initially amputated proximal sciatic nerve could retract over the relatively lengthy distance separating the area above the knee all the way to the sciatic notch where the neuroma was found. Multiple clinical improvements were noted postoperatively. At the time of surgery, the patient’s pain was significantly impacting her daily life, and she used a wheelchair. In the months following surgery, the patient’s pain improved, and she was able to ambulate with a cane and prosthesis.

Traumatic neuromas are benign masses of entangled and disorganized regenerated nerve fibers that can occur after various forms of trauma, including operations and amputation.¹ Radiologically, they are difficult to distinguish from nerve sheath tumors because of their similar presentation and because both tumors enhance with intravenous contrast.⁶ Neuromas are sometimes described as stump neuromas when there is no distal nerve segment present.⁷ Although most stump neuromas are asymptomatic, the literature reports symptomatic neuromas of the lower extremities at 12%–29%.⁸ The symptoms that most commonly occur are pain and paresthesia.¹ Histologically, they have a disordered appearance and are seen to be a nonencapsulated combination of axons, Schwann cells, endoneurial cells, and perineurial cells.⁹ These traumatic neuromas are surrounded by dense fibrous stroma.⁹ Treatment options are debated and can vary between conservative and surgical management. Conservative management includes pharmacotherapy, injections, transcutaneous magnetic stimulation, or cryotherapy and radiofrequency ablation.¹ Surgical management consists of resection that can be combined with ethanol injection or with targeted nerve implantation.¹ In this case, suture ligation was chosen over newer techniques such as targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) because of the anatomical location of the proximal stump in the sciatic notch. TMR or RPNI would have involved a posterior and then anterior approach to expose muscle and nerves in the intrapelvic lumbosacral plexus to anastomose the normal proximal sciatic stump to a target nerve or into muscle. The comorbidities and relatively frail nature of our patient did not seem to be worth the risk of this more extensive surgery. The recent literature on TMR in patients with lower-extremity amputation has not involved a case like ours, and most patients were less than 10 years removed from initial amputation, whereas our patient was 24 years removed.^10,11 Overall, it is important to include traumatic neuroma on the differential when treating peripheral nerve tumors but also phantom limb pain after amputation.

Lessons

Traumatic neuromas are a complication that can occur after amputation and present with symptoms similar to phantom limb pain. Imaging should be considered in patients with phantom limb pain to assess for the presence of a peripheral mass and evaluate for subsequent resection. Surgical removal of a traumatic neuroma may improve pain previously thought to be associated with phantom limb pain. Further research should be done to explore diagnostic methods to differentiate between traumatic neuromas and phantom limb pain.

Author Contributions

Conception and design: all authors. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: all authors. 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: Chiocca. Administrative/technical/material support: Halloran. Study supervision: all authors.