ULTRASONOGRAPHIC DIAGNOSIS OF RECURRENCE AFTER EXCISION OF AN INTERDIGITAL NEUROMA
August 8th, 1997
Stuart E. Levine, MD, Mark S. Myerson, MD,
Patricia P. Shapiro, MD, and Steven L. Shapiro, MD
We retrospectively reviewed the records of 20 patients (21 feet) with previous interdigital neuroma resections and symptoms suggestive for, but not diagnostic of, recurrent neuroma. Sonography was performed when clinical findings supplemented by local anesthetic block did not conclusively confirm the presence of recurrent neuroma. Studies performed in 13 patients (14 feet) were positive for recurrent neuromas. Three studies were indeterminate. The remaining four studies were negative for recurrent neuroma. The ultrasound studies were performed at an average of 19.2 months (range, 2 to 82 months) after the resection. Nine patients with 11 previous interdigital neuromas underwent ultrasonographic examination of the forefoot and subsequent revision neuroma resection. At surgery, gross and histologic findings were consistent with recurrent neuroma in 10/11 cases; one patient was found to have metatarsal-phalangeal synovitis.
Ultrasonography appears to be a useful means for confirming neuroma recurrence in patients with symptoms after interdigital neurectomy when the diagnosis is not clear on physical examination.
Interdigital neuroma is an enlargement, which may be painful, of the common digital nerve at the level of the metatarsal head. It has been demonstrated histologically that this is not a true neuroma but instead appears to be the result of an entrapment syndrome.2,11 Histologically, endoneural edema and sclerosis with vascular wall thickening, perineurial fibrosis, amorphous eosinophilic deposition, and nerve fiber degeneration is seen.2,7,11
Excision of an interdigital neuroma does not always provide satisfactory relief of pain.3,5,8-10,12,13 Persistent symptoms may be related to dorsal nerve injury during the primary surgery,3 an interdigital neuroma in an adjacent space 3,19, or an unrelated source of forefoot pain such as plantar wart or synovitis.3 Incomplete resection of the interdigital neuroma9,13 or true neuroma formation at the site of nerve excision1,9,13 will also produce discomfort at the postsurgical site.
Surgery for continued pain after interdigital neurectomy has been directed at either removing a stump neuroma3,5,9,12 or cutting the nerve proximal to the neuroma to create a neuroma in a less vulnerable region.3,4 Neither of these surgeries is likely to be effective if the pain does not originate from a neuroma.
The evaluation of a patient with recurrent pain after excision of a interdigital neuroma is usually based on physical examination and diagnostic injection.3,5,12 Well localized tenderness may be present and the patient's symptoms usually are reproduced by palpation or percussion over the nerve stump. Magnetic resonance imaging has been successfully used for the diagnosis of primary6,18,20 and recurrent6 interdigital neuromas. Ultrasonography has been demonstrated to be useful for the diagnosis of primary interdigital neuromas.14-16
In the current study, we have demonstrated the utility of ultrasonography for evaluation of the patient who has previously undergone a resection of an interdigital neuroma.
Materials and Methods
Over a 3-year period, we treated 20 referred patients (16 females, 4 males) who had undergone ultrasonographic evaluation of the forefoot for recurrent pain after neuroma resection. Their mean age at the time of the ultrasound was 55.0 years (range, 27.8 to 76.4 years). The ultrasound was performed an average of 19.2 months after the initial surgery (range 2 to 82 months).
Recurrent neuroma was identified in 13 patients (14 feet). Nine of these patients subsequently underwent resection of a neuroma in the previously operated web space. For these patients, ultrasound examination had been performed an average of 28 months after the primary surgery (range, 3 to 82 months). All specimens underwent pathologic evaluation.
If the diagnosis was not clear on the basis of physical examination and selective local anesthesia injection, ultrasonographic examination was performed. When ultrasonography was positive for recurrent neuroma, revision neurectomy was recommended. If there was no evidence of recurrent neuroma, we recommended further nonoperative treatment.
Ultrasonography was performed with the patient seated on the examination table with legs extended and the ankle dorsiflexed. Each interspace of the foot was scanned in the coronal and sagittal plane. Scanning was performed from the plantar surface using a 7.5 MHZ transducer (Acuson, Mountain View, CA). The adjacent toes were manually separated and pressure was applied to the dorsum of the web space at the level of the metatarsal heads to produce widening of the web space and increase visualization. The region from the distal third of the metatarsals to the base of the proximal phalanges, including the soft tissue in the web space, was scanned.
The bony structures were echogenic with posterior shadowing. The contours were easily visualized and correlated with plain radiographs. The normal web space soft tissues were echogenic (less than bony structures) and homogeneous. The intermetatarsal ligament was not identifiable. The digital artery was identified by color doppler or pulsation. Normal digital nerves were not identifiable as they are isoechoic with the surrounding soft tissue (Fig. 1).
Recurrent interdigital neuromas were seen as poorly marginated but definite hypoechoic masses located at, or just proximal to, the level of the metatarsal head (Figs. 2 and 3). Scar tissue, on the other hand, appeared as an inhomogeneous echo texture without defined bulk, mass or form.
Four patients had no evidence of recurrent neuroma in the previously operated web space. Of these patients, one had evidence of a primary neuroma in a different web space, one had substantial scarring in the previously operated web space, one had a 6-mm mass felt to be of doubtful clinical significance, and one had synovitis of the second and third metatarsal phalangeal joints. For three patients, the study was indeterminate. Two of these had findings the ultrasonographer could not differentiate as scar or recurrent neuroma. One patient who was more that 5 years postsurgery had an indeterminate soft-tissue inhomogeneity.
For the 13 patients (14 feet) with evidence of a recurrent neuroma, the primary neuroma excision had been performed in the second web space in 5 feet, the third web space in 6 feet, and the second and third web spaces in 3 feet. Of these 13 patients (14 feet), 9 patients (9 feet) underwent revision neurectomy. One additional patient underwent nerve transection proximal to the neuroma site. Three patients (4 feet) have not had revision surgery at this time. Two of these patients have chosen not to have surgery. One patient (2 feet) had more diffuse pain which was difficult to attribute solely to a recurrent neuroma. Local injection into the involved web space on one foot provided incomplete relief leading to the decision not to perform further surgery.
A total of 10 neuromata that were identified on ultrasonographic examination were excised. In two feet, a second (primary) neuroma in a different interspace was identified by ultrasonography and was removed at the same time as the recurrent neuromata, since it was felt to be symptomatic. Four patients underwent excision of a recurrent second web space neuroma. Two patients underwent excision of a recurrent third web space neuroma. One patient underwent excision of recurrent second and third web space neuromata. Two patients who had previously had neuroma excision in the second web space alone underwent excision of a primary neuroma in the third web space at the time of the excision of the recurrent neuroma in the second web space.
Surgical findings and pathologic examination were consistent with neuroma in all specimens.
Continued neurologic pain after excision of an interdigital neuroma may be due the formation of an amputation stump neuroma. In performing an interdigital neurectomy, it is hoped that the amputation stump neuroma that forms will be in a protected, non-weight-bearing portion of the foot.1 Mann and Reynolds13 felt that recurrent symptoms were due to adherence of the stump neuroma to the plantar aspect of the metatarsal head. In a cadaveric study, Amis et al.1 demonstrated plantarly directed branches of the interdigital nerve, which they felt may play an important role in the formation of symptomatic stump neuromata. These branches may tether the cut end of the nerve, preventing its proximal retraction, leaving it in the weight-bearing region of the foot. Secondly, if these nerve fibers are cut, traumatic neuromata may form, resulting in plantar tenderness.
Recurrent interdigital neuromas appear to develop more rapidly than primary neuromas. On ultrasound examination, the neuroma appears heterogeneous with mottled areas of increased and decreased echogenicity for the first 6 to 12 postoperative months. The appearance then changes to a vague, poorly marginated, infiltrative hypoechoic mass. Over time, the mass becomes more discreetly marginated until the recurrent neuroma appears identical to a primary neuroma sonographically. The recurrent neuroma is usually located proximal to the primary neuroma.
Continued pain after interdigital neuroma resection may be due to a second neuroma in an adjacent interspace.3,17,19 In our series of 20 patients (21 feet) who had pain after neuroma resection, three primary neuromas were identified in web spaces adjacent to the previously operated one.
A patient with a recurrent neuroma will often have complaints similar to those they had before surgery. Particularly in patients who had little or no pain-free periods, it is reasonable to suspect that the resected interdigital neuroma is not the primary cause of their preoperative symptoms. Failure to correctly diagnose the primary cause for the patients symptoms may explain why a substantial number of patients have persistent pain after revision interdigital neurectomy.3,9 In our series, one patient was shown to have metatarsophalangeal synovitis without evidence of recurrent or primary neuroma.
Ultrasonography has previously been demonstrated to be useful for the diagnosis of primary interdigital neuromas.14-16. In the current study, we have delineated the positive predictive value of ultrasonography in demonstrating recurrent neuroma formation in patients with pain after interdigital neurectomy. All nine patients who had a positive ultrasound and underwent excision had gross and histologic evidence for a recurrent neuroma. Two additional primary neuromas were correctly identified with ultrasonography in these feet.
Ultrasonography appears to be useful for confirming the existence of a recurrent neuroma after interdigital neurectomy. Use of this technique may assist the surgeon in evaluating the patient with continued symptoms after interdigital neurectomy when the diagnosis is not clear on physical examination.
The authors wish to thank Elaine P. Bulson for editorial support in the preparation of this manuscript.
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Fig. 1. Transverse image including the fourth, third, and second metatarsal heads (left to right). A, sketch of area (shaded) scanned. B, ultrasonogram shows normal echogenicity in the third-fourth interspace and a well-marginated hypoechoic mass consistent with a primary Morton's neuroma in the second-third interspace. C, outline definition.
Fig. 2. Transverse image including the fourth and third metatarsal heads (left to right). A, sketch of area (shaded) scanned. B, ultrasonogram showed a poorly marginated, infiltrating, hypoechoic mass within the fourth-third interspace, surgically proven to be a recurrent Morton's neuroma. C, outline definition.
Fig. 3. Sagittal images show primary (A, ultrasonogram; B, outline) and recurrent (C, ultrasonogram; D, outline) neuromas. Note the infiltrative, less discretely marginated nature of the recurrent (C, D) neuroma.