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Benign schwannoma of the medial dorsal cutaneous nerve of the foot: A case report

Posted on July 31, 2020 | Comments Off on Benign schwannoma of the medial dorsal cutaneous nerve of the foot: A case report

by Mark Capuzzi DPM1, Zachery Weyandt DPM1, Dawn Masternick DPM2

The Foot and Ankle Online Journal 13 (2): 6

Schwannomas are benign soft tissue tumors of Schwann cells in the peripheral nerve system that can occur in the foot and ankle with preference for the posterior tibial nerve. A 60-year old female with a histologically diagnosed schwannoma of the medial dorsal cutaneous nerve is described in a location that is atypical according to the literature. These soft tissue masses can easily be misdiagnosed, and MRI studies can be inconclusive in determining possible malignancy. Clinicians should be suspicious and include malignant peripheral nerve tumors in their differential diagnosis with excisional biopsy as a way of definitive diagnosis.

Keywords: schwannoma, foot and ankle tumor, soft tissue mass, medial dorsal cutaneous nerve

ISSN 1941-6806
doi: 10.3827/faoj.2020.1302.0006

1 – University of Louisville Podiatric Medicine and Surgery Residency/Fellowship, Louisville, Kentucky
2 – Tipton and Unroe Foot and Ankle Care, Kentucky

* – Corresponding author: mjc5527@gmail.com

Neurilemoma was originally described histologically by Verocay in 1908, with the term schwannoma being coined by Abadie and Argaud some 20 years later [1]. Schwannomas are a variety of peripheral nerve sheath connective tissue masses that arise in the periphery usually of benign nature. This group also includes neurofibromas and malignant peripheral nerve sheath tumors (PNSTs) that are classified based on their histological appearance. Schwannomas are solitary encapsulated tumors histologically described by homogenous arrangement of palisading cells (Verocay bodies) and exhibit hypercellular and hypocellular areas of devoid spindle cells; otherwise known as Antoni A and Antoni B [2]. These lesions can have major clinical impact on the neurocutaneous diseases neurofibromatosis 1 and neurofibromatosis 2 or can be seen as isolated occurrences without systemic involvement [3].

In a retrospective single-center study by Toepher, et al., 25.2% of all foot and ankle tumors were reported to be benign soft tissue tumors, of which, 16 different variants exist. The most common of which are hemangiomas, pigmented villo-nodular synovitis, superficial fibromatosis, and schwannomas, respectively [4]. Neurinoma/schwannoma account for about 1-10% of all soft tissue tumors in the foot and ankle. It is estimated that 1% of cases have malignant potential [4].

Schwannomas are most frequently seen in the trunk, head, neck, retroperitoneum, brachial plexus, and posterior tibial nerve [5]. Multiple case studies have been published in recent years describing these tumors in the foot and ankle, usually in connection with the posterior tibial nerve, but less commonly also seen in areas of the digits and the forefoot [6,7,8,9].

In this detailed case report, we describe a 60-year old woman with a schwannoma of the medial dorsal cutaneous nerve. The palpable mass arises in the dorsal midfoot associated with the tarsometatarsal joint, an area that has only been reported once in the literature and extending distally over the 2nd metatarsal base. The report includes a thorough clinical history, physical examination, diagnostics, as well as a histopathological description.

Case Report

A 60-year old Caucasian female presented to the attending surgeon’s private clinic with a chief complaint of a painful right midfoot mass that began one year previous. She felt the lesion had been increasing in size over time and worsening in severity of pain. She recalls the pain began only in shoe wear, as a rubbing irritation, but upon presenting to the clinic was painful also while walking barefoot. The patient’s history revealed trauma to the area of the mass two years ago when a large sign was dropped on her foot that she did not seek medical care for, leaving her foot bruised. She denied any other source of pain and other cutaneous masses as well as any history of puncture wounds or foreign bodies. Her medical history includes tubular adenoma, hemorrhoids, osteopenia, and a non-descript heart murmur. She denied taking any prescription medications, using only calcium supplements daily for her osteopenia.

Clinical examination revealed an apparently healthy female in no acute distress. A family history was non-contributory for soft tissue masses and a review of systems was unremarkable. Vascular examination revealed palpable pedal pulses and a brisk capillary refill time to all digits. Neurological examination revealed normal sensory sensations to digits and foot without deficit. No Tinel’s or Valleix’s signs were noted. Biomechanical examination revealed pes planus foot type with normal range of motion of all joints and without structural deformities. Dermatological examination revealed an oval, mobile, semi-compressible, tender to palpation, subcutaneous mass beginning over the 2nd tarsometatarsal joint extending over the base of the 2nd metatarsal. The bulk of the mass was distal to the 2nd tarsometatarsal joint. The mass was non-adherent to underlying structures without signs of infection, drainage, or irritation. There was no open wound in the area or bony exostosis. The mass measured 1.0cm x 1.0cm. The mass did not transilluminate nor have a palpable pulse.

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Figure 1 T1 Sagittal and T2 Axial MRI.

Differential diagnoses discussed included: fibroma, neuroma, neurofibroma, lipoma, foreign body, and benign/malignant peripheral nerve sheath tumors. The patient was educated and was presented treatment options for a ganglion cyst during her first appointment. She agreed to receive a corticosteroid injection in the area of the mass. She returned one month later without improvement and received a second injection, with aspiration attempted, revealing no fluid collection. At the 3rd visit, the patient again demonstrated no signs of improvement and worsening pain. An MRI was ordered at this time as there was a lowered clinical suspicion for a ganglion cyst (Figure 1).

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Figure 2 Schwannoma immediately visible in superficial fascia after incision.

The impression of the MRI report read a 6mm x 6mm x 4mm subcutaneous nodular lesion, superficial tear contacting the second extensor tendon anterior to the second TMT joint.

The radiologist suggested statistically the mass was a synovial/ganglion cyst but could not confirm or deny a benign or malignant soft tissue mass on a non-contrast MRI. The patient was educated on the results of her MRI and the inconclusive results. Upon discussion of an additional attempted aspiration versus further work-up including a MRI with contrast, a MRI with contrast was ordered. The second MRI reported a fairly uniform enhancement of the previously noted well-circumscribed subcutaneous nodular lesion along the dorsal aspect of the midfoot. The enhancement aspect of the image favored a non-cystic benign or malignant soft tissue mass in which surgical excision was recommended. Surgical excision was proposed and agreed upon by the patient.

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Figure 3 Schwannoma after surgical dissection with distal nerve continuation.

She was taken to the operative room and monitored anesthesia care was exercised in addition to a V-block of local anesthetic just proximal to the soft tissue mass. An approximately 3cm longitudinal incision was made directly over the mass. Careful and meticulous dissection immediately revealed a yellow, firm, and oval mass in the subcutaneous tissue that was encapsulated (Figure 2). The mass was freed from its surrounding structures with ease. Upon further blunt dissection, nerve-like structures were found to be projecting from the mass in a proximal and distal direction with abnormal thickening. The nerve-like projections mimicked the course of the medial dorsal cutaneous nerve as it extends to the 2nd interspace (Figure 3). A measurement of 5mm proximal and distal to the mass was marked and the nerve was transected and removed from the body in its entirety. The specimen was placed in formalin and prepared for histopathological examination (Figure 4).

Figure 4 Pathological specimen of schwannoma without distal and proximal nerve projections.

Upon visual inspection, no further remnants of the mass or abnormal nerve remained and the area was irrigated. Deep structures were approximated with vicryl sutures and skin was closed with prolene. The patient was placed in a soft dressing to the operative foot.

The pathology report grossly described a soft tissue mass of the right foot received in formalin, as yellow-white soft and feathery tissue in multiple fragments. The pathologist described a low power photomicrograph showed a well-circumscribed and encapsulated nodule with no infiltrating borders and no identifiable necrosis. High power photomicrograph showed bland spindle cell proliferation with eosinophilic cytoplasm, indistinct cell borders, and tapered nuclei (Figures 5 and 6). Mitotic figures were inconspicuous. Immunohistochemical stain for S100 was strongly and diffusely positive in the neoplastic cells. Schwannoma was favored by palisading nuclei and encapsulation.

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Figure 5 H&E Histopathological image.

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Figure 6 S-100 stain positive.

Post-operative protocol for the patient included full weight-bearing as tolerated in a surgical shoe to the operative side. She was evaluated two weeks out from surgery, demonstrating a well healed surgical site without wound dehiscence, infection, or pain. Sutures were removed at this time and the patient returned to normal shoe gear. She was encouraged to complete range of motion exercises at this time. The patient’s follow up at 4 weeks again demonstrating a healed surgical wound in the absence of pain. The patient was satisfied with her surgical results. A phone call was conducted 6 months post-operatively, and the patient denied any pain, wound complications, no neurologic symptoms, and noted she was extremely satisfied with the result.

Discussion

The diagnosis of a Schwannoma, can pose a challenge for a clinician in the office setting. As reported, our patient was originally thought to present with a ganglion cyst which was treated with steroid injections and attempted aspiration. For any benign soft tissue mass, multiple differential diagnosis should be thought of prior to intervention, such as, but not limited to, ganglion cyst, fibroma, neuroma, neurofibroma, lipoma, and benign/malignant peripheral nerve sheath tumors. Good practice dictates that if the mass is not responding to conservative measures, biopsy with histopathological examination is the standard of care. Excisional biopsy is the accepted technique in cases of the foot and ankle with small lesions (< 2cm) located in the subcutaneous tissue as was the case in our report [10].

Schwannomas’ have been reported in the foot and ankle literature, however, rarely in the dorsal midfoot. To the author’s knowledge only one other case has been reported in the location of the tarsometatarsal joint [11]. An area not uncommon to find ganglion cysts corresponding to an underlying joint. Knight, et al., retrospectively review 234 benign solitary schwannomas and describe their peripheral nerve distribution. Of 64 schwannomas involving the lower limb and pelvis, they reported the most commonly involved nerves included the sciatic nerve (n = 15), tibial nerve (n = 21), and common peroneal nerve (n = 15) [12]. Kransdorf, et al., described one of the largest retrospective review studies regarding benign soft tissue lesions. They looked at over 18,000 benign soft tissue lesions, and further categorized them via distribution of specific diagnosis by age, sex and location. Regarding total body distribution, schwannoma prevalence in the foot and ankle was 0.09% (81/895). No definitive predilection for male vs. female has been noted in the literature. There is a wide age range, with the majority of patients being between the ages of 50-70 years old [13].

Topfer, et al., as part of a retrospective study looked at the data of patients that were treated for foot and ankle tumors between June 1997 and December 2015. The primary aim of the study was to describe the prevalence, demography, and anatomical distribution of the tumors. This study presented an analysis of the second largest population of patients, with current literature. Out of 7487 musculoskeletal tumors, 413 cases (5.52%) of tumors of the foot and ankle were included. There were 147 soft tissue tumors (36%), of those 104 (71%) were benign and 43 (29%) were malignant. Benign soft tissue tumors, including all variants, were most commonly located in the ankle and midfoot. Malignant soft tissue tumors were most commonly at the midfoot. Schwannomas specifically were most common in the hindfoot and least common in the midfoot. Of the 104 benign soft tissue tumors, only 11 were found to be Schwannomas with zero being found in the midfoot and only one in the forefoot [4]. Malignancy should be suspected early in treatment, with regard to the aforementioned literature at hand.

Hao, et al., conducted a literature review of schwannomas that included 46 reported masses. Of the 46 schwannomas, 14/46 were on the ankle, 14/46 plantar aspect of foot, 9/46 heel, 3/46 interdigital spaces, 1/46 dorsal foot over 4th and 5th metatarsal, 5/46 unreported anatomical location. Again, none were found associated with the tarsometatarsal joint or located in the midfoot [7].

Conclusion

To our knowledge this is the first reported case of a schwannoma associated with the dorsal 2nd tarsometatarsal joint, and one of two reported cases overlying the tarsometatarsal joint complex. They can be difficult to diagnose clinically and become more challenging when mimicking a common ganglion cyst location. A detailed medical history is to be performed on all patients, with a high index of suspicion in patients with a familial history or active history of Neurofibromatosis Type 1 or Type 2. Recurrence and failed attempts of injections and/or aspirations should warrant the podiatric physician to have a detailed discussion regarding surgical intervention. MRI can be an effective diagnostic and surgical planning tool; however, surgical excision and histopathological examination is considered to be the gold standard. Particularly in cases where MRI cannot definitively diagnose a mass and is inconclusive in regard to a mass’s malignancy.  Schwannomas may resemble other soft tissue tumors of the foot and diagnosis is generally made via histopathological findings status-post excision, as was the case in this report.

Funding Declaration: N/A

Conflict of Interest Declaration: No Conflicts of Interest to Report

Acknowledgements: University of Louisville Department of Pathology

References

  1. Spiegl, P. V., Cullivan, W. T., Reiman, H. M., & Johnson, K. A. (1986). Neurilemmoma of the Lower Extremity. Foot & Ankle, 6(4), 194–198.
  2. Carvajal JA, Cuartas E, Qadir R, Levi AD, Temple HT. Peripheral nerve sheath tumors of the foot and ankle. Foot & Ankle International. 2011;32(2):163-167.
  3. Ferner RE, O’Doherty MJ. Neurofibroma and schwannoma. Curr Opin Neurol. 2002;15(6):679–684.
  4. Toepfer A, Harrasser N, Recker M, et al. Distribution patterns of foot and ankle tumors: A university tumor institute experience. BMC cancer. 2018;18(1):735.
  5. Tladi MJ, Saragas NP, Ferrao PN, Strydom A. Schwannoma and neurofibroma of the posterior tibial nerve presenting as tarsal tunnel syndrome: Review of the literature with two case reports. Foot, The. 2017; 32:22-26.
  6. Daniel M, Waters D, Chen C, and Brouyette N. Posterior tibial nerve schwannoma in a multiple myeloma patient: A case report. SAGE Open Med Case Rep 2019; 7:2050313×19838441.
  7. Hao X, Levine D, Yim J, et al. Schwannoma of foot and ankle: Seven case reports and literature review. Anticancer research. 2019 Sep;39(9):5185-5194.
  8. Jabra, A. S., & Godoy, J. (2019). Rare Schwannoma Nerve Tumor in a Lesser Toe: A Case Report. Journal of the American Podiatric Medical Association, 109(4), 322–326.
  9. Merritt, G., 4th, Ramil, M., Oxios, A., & Rushing, C. (2019). Schwannoma of the plantarmedial aspect of the foot: A case report. Foot (Edinburgh, Scotland), 39, 85–87.
  10. Downey MS, Gredlein CM, eds. Chapter 92: Soft tissue masses. In, Southland J. T., Vickers D. F., Boberg J. S., Downey M. S., Aprajita N. and Rabjohn L. V., eds. McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery, 4e ed. Lippincott Williams & Wilkins; 2013.
  11. Jacobson G, Edwards M. Neurilemoma presenting as a painless mass on the dorsal of the foot. Journal of the American Podiatric Medical Association. 1993;83(4):228-230.
  12. Knight DM, Birch R, Pringle J. Benign solitary schwannomas: a review of 234 cases. J Bone Joint Surg Br. 2007;89(3):382–387.
  13. Kransdorf MJ. Benign soft-tissue tumors in a large referral population: Distribution of specific diagnoses by age, sex, and location. American Journal of Roentgenology. 1995;164(2):395-402.

 

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Longitudinal plantar approach for excision of interdigital perineural fibroma of the foot: A case series and literature review

Posted on March 1, 2016 | Comments Off on Longitudinal plantar approach for excision of interdigital perineural fibroma of the foot: A case series and literature review

by George Flanagan1, Ian Reilly1,2*pdflrg

The Foot and Ankle Online Journal 9 (1): 1

Background:  There is an array of clinically and academically derived opinion as to the correct surgical approach to the intermetatarsal space, most frequently to excise a symptomatic interdigital perineural fibroma (aka Morton’s Neuroma).  The purpose of this retrospective case series was to evaluate the patient outcomes, and sequelae following a longitudinal plantar incision for excision of interdigital perineural fibroma.
Method: This is a retrospective case series of forty-two patients who underwent excision of interdigital perineural fibroma utilizing a longitudinal plantar incision between 2012-2014.  All patients were reviewed at two weeks, four weeks and six months post operatively.  Patient and clinician outcome measures were captured by means of the Manchester-Oxford Foot Questionnaire (MOXFQ) and Patient Satisfaction Questionnaire 10 (PSQ-10).
Results: Forty two patients (forty eight excisions) were assessed both pre operatively and post operatively.  95.2 percent of patients felt their foot was better or much better at six months post operatively.  The average post-operative PSQ-10 score was 85.05 (SD +/- 14.3).  A significant reduction in all three MOXFQ domains was observed.  Four patients had surgical sequelae; only one patient reported no improvement in pain post operatively.  No patients reported worsening symptoms.
Conclusion:  Producing excellent patient outcomes with only minimal complications, this case series substantiates the growing literature showing that excision of interdigital perineural fibroma through a longitudinal plantar incision is both safe and effective.

Key words: interdigital perineural fibroma, soft tissue mass, neuroma, fibroma

ISSN 1941-6806
doi: 10.3827/faoj.2016.0901.0001

1 – Department of Podiatric Surgery, Northamptonshire Healthcare Foundation Trust, England
2 – Private Practice, Northamptonshire, England
* – Correspondence: pod.surgeon@virgin.net

Interdigital perineural fibroma (Morton’s neuroma, interdigital neuroma, Morton’s metatarsalgia) is both a commonly described pathology as well as a frequently encountered affliction.  Although commonly affiliated with Thomas Morton’s description of 1876 (Morton, 1876), of only the third intermetatarsal space, arguably historic precedence can be attributed to either Civinini, (1835), Durlacher, (1845) or Tubby, (1912).

The incidence of interdigital perineural fibroma (IPF) is three-fold in the middle aged female population in comparison to their male counterparts (Naraghi et al, 2014). Symptoms commonly include paroxysmal pain and paresthesia of the pedal web space (most commonly the third) and adjacent digits.  The preferred description of an ‘entrapment neuropathy’ is now frequently utilized (Hassouna & Singh, 2005).  Despite the plethora of literature which exists for this common condition, a continuum of disparity regarding its etiology remains.

Diagnosis is by a thorough mixture of both symptomology and clinical examination.  Musculoskeletal ultrasound and magnetic resonance imaging have been shown to be sensitive diagnostic tools (Sharp et al, 2003).  There exists a treatise of nomenclature relating to this condition.  Although many historic reports entitle IPF as a ‘tumor’, recent histopathologic studies have formalized its histology as a perineural fibroma (Pazzaglia et al, 1996), that of inflammation and fibroblastic proliferation around a nerve.  Despite this, most studies cite an IPF as a benign swelling occurring at the bifurcation of the plantar interdigital nerve.

If symptoms of IPF are refractory despite exhausting conservative treatment modalities, then surgical intervention is indicated (Akermark et al, 2008).  Numerous surgical approaches and procedures have been described for this condition.

Disaccord is prevalent regarding incision placement, particularly whether the incision should be approached dorsally or plantarly (Wilson & Kuwada, 1995).  Evidence does not favor any particular approach to incision, despite this, many practitioners surreptitiously avoid a plantar incision due to concerns surrounding cicatrix, particularly hypertrophic scar formation and intractable plantar keratosis (Hassouna & Singh, 2005).  This case series highlights the method and outcomes relating to patients (n=42) who underwent complete excision of IPF via a longitudinal plantar incision.

Methods

Between 2012-2014 consecutive patients (n=97) who had refractory symptoms despite conservative treatment intervention underwent surgical excision.

Inclusion and exclusion criteria

Of the 97 patients who underwent surgical excision:

Those patients who had surgery performed utilizing a dorsal approach (n=11), patients who had undergone simultaneous bilateral procedures (n=5) and patients who underwent excision in combination with other surgical procedures (n=9) were excluded from the study.  Patients for whom post-operative outcome data was unavailable (n=30) were also excluded.  Patients who had undergone excision of a perineural fibroma unilaterally and in isolation were subsequently included (n=42).  Successive outcome data for at least 6 months was a prerequisite.

Surgical technique

All surgery was undertaken or supervised by the second author (IR).  Patients were all admitted on a day surgery ambulatory basis.  General anesthesia with regional local anesthetic block was used in a minority of patients (4, 9.5%), the majority of patients underwent surgery with regional ‘ankle block’ anesthesia alone.  Standard surgical asepsis and infection control measures were observed.  Surgery took place within a laminar airflow (Howorth Exflow 90) operating theatre.  The procedure was performed utilizing a pneumatic ankle tourniquet set at 80-100 mmHg above the patients’ recorded systolic blood pressure.

A longitudinal plantar incision was made (Figure 1).  The incision extends from the edge of the adjacent web space distally to just beyond the level of the metatarsal heads proximally.  Vessel management was undertaken utilizing bipolar cautery.

Fig1

Figure 1 Plantar longitudinal incision.

Fig2 

Figure 2 Highlighting digital bifurcation.

Fig3

Figure 3 Proximal tracking of nerve.

Fig4

Figure 4 Wound closure.

Utilizing blunt dissection carefully, navigating through the plantar fat pad, the pathological nerve is identified, perineural adhesions were bluntly released ensuring integrity of the surrounding soft tissue architecture.  Visualization and adhesion neurolysis was performed distally at the level of digital bifurcation (Figure 2).

Proximally blunt dissection was undertaken (Figure 3) until normal nerve diameter and visualization was encountered.

The plantar digital nerve was resected distally at its digital bifurcation, and proximally where approximately 10mm of normal nerve had been visualized.  The remaining proximal nerve stump was cauterized and displaced proximally.  Hemostasis was achieved again using bipolar cautery.  The surgical site was then flushed with saline and skin closure achieved with 3-0 monofilament polypropylene suture utilizing a horizontal mattress technique (Figure 4).

Post-operative management

Protocol for post-operative analgesia included co-codamol 30/500 one or two tablets QDS and diclofenac 50mg TDS (PRN).  Co-codamol was replaced for Tramadol 50mg QDS in cases of allergy or intolerance.  All patients were placed in a compression dressing utilizing a universal post-operative shoe (Benefoot) for four weeks, during which time they were allowed to weight bear for essential activities of daily living.  Patients received a wound review at two weeks and removal of sutures at four weeks.  Patients were seen finally for six month review.

Data capture and statistics

Patient reported outcome measures were recorded using paper questionnaires both pre-operatively on the day of surgery and post operatively at 6 month review.  Pre and post operatively patients were asked to complete the Manchester-Oxford Foot Questionnaire (MOXFQ) (Dawson et al, 2006) and post-operatively. In addition to the MOXFQ, patients completed The Patient Satisfaction Questionnaire 10 (PSQ-10) (Rudge & Tollafield, 2003).  Data was inputted electronically to the Podiatric Audit of Surgery and Clinical Outcome Measure (PASCOM-10) system.  During post-operative review clinician determined outcome data was also collected.

Statistics and calculations were achieved using Microsoft Excel (2010 Microsoft Corporation).

Results

Of the patients included in the study (n=42), 33 (78.5%) were female with a mean age of 52.9 (SD +/- 11.8) years (range 28-72) and 9 (21.5%) were male with a mean age of 54.8 (SD +/- 12.8) years (range 44-72).  In 25 (59.5%) cases the left foot was involved, leaving 17 (40.5%) incorporating the right foot.  Neuromas were excised in isolation in 20 (47.6%) cases from the 3rd intermetatarsal space and 16 (38.1%) from the 2nd intermetatarsal space, 6 (14.3%) cases involved both the 2nd and 3rd intermetatarsal space.  Histological confirmation of perineural fibroma was obtained in all samples excised, totaling 48 from 42 feet. (Example of excised sample sent to histology seen in Figure 5).

Fig5

Figure 5 Excised interdigital perineural fibroma.

Of the 42 patients in the study, 4 cases of surgical sequelae were recorded.  Sequelae were recorded during post-operative visits by the attending clinician utilizing electronic data capture. Of the 4 patients, 2 patients (4.7%) suffered with scar line hypertrophy, one patient required surgical revision of the scar with good long term results at six month follow up.  One patient (2.4%) had a suspected stump neuroma at 6 months post op, this patient achieved asymptomatic longevity with one infiltration of 40mg Depo-Medrone, subsequently not requiring further surgery. One patient (2.4%) had a suspected (not proven) superficial infection treated with a 7 day course of antibiotics with no long term negative effect.

Patient satisfaction was captured utilizing the PSQ10.  At 6 months post-surgery 40 (95.2%) patients felt that their foot was better or much better than compared to the original problem.  One patient (2.4%) noted that their foot felt ‘the same’ when compared to the original problem, it was this patient who subsequently required revision of hypertrophic scar formation.  One patient (2.4%) did not state how they felt.  When asked ‘would you have surgery again under the same circumstances?’, 40 (95.2%) said yes and 2 (4.8%) said no.  The majority of patients (13, 31%) were back into preferred footwear by 8 weeks, 2 patients (4.8%) by 2 weeks; 10 (21.4%) by 4 weeks; 12 (28.6%) by 6 weeks with 6 (14.3%) patients waiting until 6 months until they were normally shod.   The average PSQ10 score was 85.05 (SD +/- 14.3).

Figure 6 illustrates the MOXFQ score distribution across the 3 patient reported outcome domains.  In the walking / standing (WS) domain the average pretreatment score was 68.8 (SD +/- 21.5), the post treatment score reduced to 23.1 (SD +/- 27.4).  For social interaction (SI) scores reduced from 51.3 (SD +/- 22.3) to 14.4 (SD +/- 19.5) and in the pain (P) category, 67.1 (SD +/- 18) and 24.6 (SD +/- 22.3) respectively.  Scores in each domain exceeded the threshold (WS 12.8, SI 20.3 and P 4.6) for a clinically significant difference as defined by Dawson et al, (2007).

Fig6

Figure 6 Pre/post op comparative MOXFQ distribution.

Discussion

Interdigital perineural fibroma are a common clinical entity, despite this, there remains disparity both academically and subjectively about its etiology, pathophysiology and long term treatment.  However it is uniformly agreed that surgical intervention is required once conservative treatment has failed (Akermark et al 2013).  Despite this surgical consensus and the vast amount of literature pertaining to it there remains druthers amongst surgeons regarding the surgical approach which should be taken.

Numerous approaches to the intermetatarsal space have been described in the literature, including minimally invasive techniques (Zelent at al 2007). Minimally invasive surgical approaches to excision of IPF have been available for a number of years (Barrett & Pignetti, 1996), however such approaches are often utilized when performing procedures alternative to excision of the pathological nerve such as decompression of the deep intermetatarsal ligament (Dellon, 1992).  Excision of the fibrosed nerve in toto is the most common procedure of choice (Jain & Mannan, 2013), for this, four main approaches to the intermetatarsal space have been described, which include; the longitudinal plantar, transverse plantar, web space approach and longitudinal dorsal.

Patient satisfaction has shown to be high following IPF excision (Thomson et al, 2004).  Despite this, reports state satisfaction rates as low as 65% (Nashi et al, 1997) and as high as 100% (Colgrove et al, 2000) utilizing various surgical approaches and methods.  As such Thomson’s Cochrane review (Thomson et al, 2004) concluded that there was insufficient evidence to assess formally the effectiveness of both operative and conservative treatment for IPF.  Further appraisal of the literature also shows discourse on failure rates following surgical intervention, ranging from 3% (Giannini et al, 2004) to as high as 24% (Younger & Claridge, 1998).

Akermark et al (2013) performed one of the first prospective randomized controlled trials providing comparative data for dorsal vs longitudinal plantar approaches to excision of IPF.  Patient satisfaction and pain reduction were comparable between both groups.  A reduction in daily activity restriction was noted in both dorsal and plantar groups, 67% and 77% respectively.  Pain reduction was 96% in the plantar incision group and 97% in the dorsal group. Other studies citing similar satisfaction rates are available.  Akermark et al, (2008) in an earlier study found 86% satisfaction rates following plantar incision, Jerosch et al, (2006) showed 92% satisfaction following longitudinal plantar incision.  Wilson & Kuwada, (1995) in a 15 year follow up study of 29 patients (59 neuromas) found preference for the plantar transverse incision when compared to a dorsal incision, with 68% satisfaction rate following dorsal incision and 100% satisfaction in the plantar approach group.  Barbosa et al, (2005) & Nery et al, (2012) also advocated a plantar transverse incision reporting 89.5% and 89.4% satisfaction respectively. Similar favorable data exists for surgery performed utilizing a longitudinal dorsal incision.  Lee et al, (2011) followed patients over 10 years, 61.4% of patients were completely satisfied, however they broke down a further 38% that were satisfied with reservations, totaling an overall 99.4% satisfaction rate.

Coughlin & Pinsonneault, (2001) using a median follow up of sixty nine months found patient satisfaction high at 84% of 66 patients (74 neuromas), good / excellent results were also compiled into satisfaction rates in studies by Giannini et al, (2004) and Kasparek & Schneider, (2013) citing 77% and 76.5% respectively.  Whilst no significant difference has been concluded in the literature, particularly that comparing multiple surgical approaches (for which there are few) patient satisfaction does seem to be slightly higher in those studies utilizing the plantar incision (both longitudinal and transverse).  Two very recent studies are also showing high patient satisfaction rates following the plantar approach (Killen et al, 2015 & Kundert et al 2015), this study adds to that data, showing a patient satisfaction rate of 95.2%.  Despite there being no significant difference in patient outcomes with either approach, as noted previously in this article, there seems to be a subjective preference for dorsal incision due to concerns regarding surgical sequelae (McKeever, 1952).

Whilst concern is derived from the notion of increased risk of intractable plantar keratosis and hypertrophic scarring following a plantar approach to excision of IPF, there remains a multitude of literature showing relatively comparable rates of surgical sequelae for both dorsal and plantar approaches.  Akermark et al, (2013) studied 97 patients and found 5 complications following IPF excision through a plantar incision and 6 through a dorsal incision.  Of the plantar group three cases of small ‘pea sized’ hypertrophic scar formation and one large hypertrophic scar were noted, all were revised with superficial excision and included in the final satisfaction results.  Of the 6 complications from the dorsal group these included one resected artery as oppose to IPF (confirmed by histology), one infection, one dehiscence, one deep vein thrombosis and two patients with recalcitrant pain requiring revision surgery through a plantar incision.  Patients reported sensory loss 85% of the time in the dorsal group compared to 66% in the plantar group.  Jerosch et al, 2006 noted 2.8% of patients with problematic scars and 1.7% infection in a large cohort of 356 patients.  Barbosa et al, 2005 found one patient of a nineteen cohort to have dehiscence, with no further complications cited.  Kundert et al, 2015 in a midterm follow up study also found favorable scar sequelae with a 5.3% symptomatic scar rate in 51 feet.  Like Akermark et al, (2013), Wilson & Kuwada, (1995) compared complication rates between both dorsal and plantar approaches, in a 15 year follow up they found a 6.7% complication rate for plantar incision and a 17% complication rate for the dorsal approach.

Similar to Akermark et al, (2013) the plantar group had two cases of problematic scar formation; however, this mirrored the dorsal group who also reported two patients with pathological scar formation.  In addition to the two patients suffering with scar tenderness, the dorsal group also had six reported cases of recurrent neuroma, one hematoma and one deep vein thrombosis.  Nery et al, (2012) found a lower incidence of complication compared to other studies (6.9% patients reported a ‘fair result’), however unlike other studies focusing on plantar incisions they had a 3.8% stump re-occurrence, confirmed via histology following revisional surgery.  Studies focusing on the longitudinal dorsal approach show no significant difference in complication rates when compared to plantar incision, however the specific type of surgical sequelae differs with approach.  Lee et al, (2011), Wilson & Kawada, (1995) and Akermark et al, (2013) all report significant discomfort related to sensory loss following IPF excision through a dorsal approach with two of these studies directly comparing dorsal and plantar incisions.  The results of the two studies (Wilson & Kuwada, (1995) & Akermark et al, 2013) which directly compare multiple surgical approaches have already shown the surfeit of sequelae which may arise following a dorsal approach, in addition to this, Coughlin & Pinsonneault, (2001) also found problems related to ‘uncomfortable’ paresthesia post operatively as well as six superficial infections, one deep infection, a case of complex regional pain syndrome and adjacent metatarsophalangeal joint instability.  In this case series the complication rate deduced was 9.6% (4 patients) which averaged between the literature scrutinized, however given the small sample size an elevated complication percentage is expected.  Of the four patients with complications, two patients had satisfactory outcomes, one patient chose not to comment and one patient (2.4%) was deemed to have a failed outcome; ultimately culminating in a 95.2% satisfaction rate.

Conclusion

Whilst we have shown that there is a risk of cicatrix’s following surgery approached through the plantar surface of the foot, research infers that there is no evidence to suggest inferior patient outcomes following this approach, particularly when compared to alternative surgical approaches.  In fact the risk of adverse scarring following this approach is comparable with data derived from cohorts utilizing a dorsal incision, thus negating the argument of mechanically induced scar hypertrophy.  In fact an interesting outcome of the Coughlin & Pinsonneault, (2001) study was the 15% incidence of post-operative intractable plantar keratosis development around an adjacent metatarsophalangeal joint following a dorsal incision. This could be a potential side effect of division of the deep intermetatarsal ligament, which requires further research in the future.

This case series produced excellent patient outcomes, in common with recent literature; a significant reduction in pain with increased mobility and social inclusion.  The existing literature already justifies the longitudinal plantar approach to excision of intermetatarsal perineural fibroma, showing a low (and less varied) complication rate: this case series substantiates this.

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