# Introduction

chwannomas are benign, encapsulated tumors derived from myelin sheath of nerves. (1) They originate from Schwann cells of neuroectoderm and as they expand they can compress nerves leading to pain, weakness, and numbness. Schwannomas usually occur in the head and neck region and are uncommon in extremities. (2) They are the most common type of peripheral nerve sheath tumor, with no gender predisposition, nonspecific age group but risk factors include trauma and neurofibromatosis type 2. (3) The tumor is slow growing and eccentric to the nerve fibers. Malignant transformation of schwannoma is very rare. The clinical diagnosis is often straightforward; however, delay for many years have been reported in schwannoma of the posterior tibial nerve as symptoms usually mimic entrapment neuropathy or lumbosacral radiculopathy.

In cases with posterior tibial nerve schwannoma, nerve conduction velocity studies can be abnormal, but, a schwannoma often does not interfere with nerve function, therefore delayed conduction velocities are nonspecific for this lesion. (4) Ultrasound can confirm the presence of the schwannoma, but magnetic resonance imaging (MRI) is the modality of choice to identify the tumor, with its margins and characteristics. (5) Nevertheless, MRI cannot distinguish between malignant and benign tumors. (6) Author ? ? ? ¥: Department of Orthopedic Surgery and Traumatology, Saint Georges University Medical Center, Balamand University, Achrafieh, Beirut, Lebanon. e-mail: josephmaalouly2@gmail.com Author ?: Department of Orthopedic Surgery and Traumatology, Clemenceau Medical Center.


# II.


# Case Report

A 39 y.o. Male patient previously healthy presented with left foot pain and numbness of 2 months duration. Patient denies any history of trauma and has no history to suggest neurofibromatosis. On physical exam, a small mass was palpated posterior to the medial malleolus with a positive Tinel sign. Radiographs were normal and requested MRI revealed a nerve sheath tumor (fig 1), most likely a schwannoma, adhering to the flexor hallucis longus tendon and posterior tibial nerve roots. Removal of the tumor is scheduled.

Under general anesthesia, using a medial incision posterior to the medial malleolus and under microscope magnification (fig 2 and 3), microdissection was performed, and the posterior tibial nerve was tagged using vessel loop proximally and distally, the mass was excised measuring 1.1x0.9 cm and is sent to pathology. This is followed by irrigation, hemostasis, and closure of the wound. The patient is discharged the second-day postop with minimal pain, and full weight bearing ambulation. The histologic report confirmed the diagnosis of the posterior tibial nerve schwannoma with no evidence of malignancy (fig 4). The patient's swelling and numbness resolved within a few weeks, and he resumed his daily activities without discomfort.


# III.


# Discussion

The most common tumors of the peripheral nerve sheath are Schwannomas with infrequent occurrence in lower extremities. (7,8) They are slow growing tumors with a very low rate of malignant transformation. Few cases reported in the literature whereby schwannoma of posterior tibial nerve shows compression neuropathy. ( 9) In all reported cases, complete surgical excision showed good results with symptoms resolution.

A peculiar aspect of these tumors is a delay of diagnosis. Nawabi and Sinisi (9) in their series revealed a mean time diagnostic delay of 86.5 months.

Surgical excision is the treatment modality of choice once the diagnosis is clear. (10) All similarly reported cases gave good results with no recurrence when the dissection is thorough. (11) Based on our case and literature review, we believe that any patient presenting with symptoms of neuropathy of the foot without apparent evidence of lumbosacral radiculopathy or compression neuropathy should be investigated further. The mass may not be palpable and delay in diagnosis is common as they are usually deep or misdiagnosed (9). A complete physical exam is crucial in these cases, whereby a positive Tinel sign along the course of the nerve may raise our suspicion of the diagnosis.

Furthermore, the use of a microscope is crucial, to avoid damage of fascicles and for thorough excision of the tumor. (11) IV.


# Conclusion

From our case, a schwannoma of the posterior tibial nerve could present as tarsal tunnel syndrome with a positive Tinel sign and a palpable mass. MRI confirms the diagnosis. Suspicion should remain high for these tumors as misdiagnosis occurs frequently which leads to wrong treatment administration and failure of therapy. Complete excision of the lesion by thorough dissection taking care to protect the nerve fibers with the aid of microscope magnification is the ideal way of managing such cases.    
1![Figure 1: (a) Coronal MRI showing enhancement of lesion with contrast adhering to posterior tibial nerve (b) Axial MRI cuts showing enhancement of lesion with contrast (c) Sagittal MRI cuts showing enhancement of lesion with contrast adhering to flexor hallucis tendon](image-2.png "Figure 1 :")
2![Figure 2: Schwannoma of posterior tibial nerve on medial aspect of ankle](image-3.png "Figure 2 :")
34![Figure 3: Schwannoma of posterior tibal nerve excised](image-4.png "Figure 3 :Figure 4 :")
![](image-5.png "")
			© 2019 Global Journals
		
		
			

				


* 
	
		
		
			REFerner
		
		
			MJO'dohertyneurofibroma
		
		
			Schwannoma
		
	
	
		Curr Opin Neurol
		
			15
			
			2002
		
	




* 
	
		Neurilemoma of the medial plantar nerve: a case report
		
			GStill
		
	
	
		J Foot Ankle Surg
		
			40
			4
			
			2001
		
	




* 
	
		Tarsal tunnel syndrome secondary to schwannoma of the posterior tibial nerve
		
			KatrinaHallahan
		
		
			JessicaVinokur
		
		
			SarahDemski
		
		
			BeverlyFaulkner-Jones
		
		10.1053/j.jfas.2012.12.020
	
	
		John Giurini J Foot Ankle Surg
		
			53
			1
			
			2014 Jan-Feb. 2013 Aug 13
		
	
	Published online




* 
	
		TuzunerTarsal tunnel syndrome secondary to neurilemoma of the medial plantar nerveJ Foot Surg
		
			ATAydin
		
		
			SKaraveli
		
		
			1991
			30
			
		
	




* 
	
		SawhneyImaging benign soft tissue lesions of the foot
		
			SMoholkar
		
		
			JS
		
	
	
		Appl Radiol
		
			38
			10
			2009
		
	




* 
	
		KuntzMagnetic resonance neurography of peripheral nerve lesions in the lower extremity
		
			C
		
	
	
		Neurosurgery
		
			39
			4
			
			1996
		
	




* 
	
		Schwannoma of the Posterior Tibial Nerve
		
			TanyaJudd
		
		
			TaunnaJones
		
		
			LaurenThornberry
		
	
	
		Journal of the American Podiatric Medical Association
		
			104
			5
			
			2014. September 2014
		
	




* 
	
		Centrally Located Schwannoma of Posterior Tibial Nerve Presenting As Lumbosacral Radiculopathy
		
			SBanshelkikar
		
		
			PNistane
		
	
	
		Journal of Orthopaedic Case Reports
		
			5
			2
			
			2015 April-June
		
	




* 
	
		Schwannoma of the posterior tibial nerve -The problem of delay in diagnosis
		
			Nawabi
		
		
			MarcoSinisi
		
		89.814-6.10.1302/0301-620X.89B6.19077
		
			2007
		
	




* 
	
		Schwannoma of the tibial nerve sheath as a cause of tarsal tunnel syndrome-A case study
		
			HLMilnes
		
		
			JCPavier
		
	
	
		Foot
		
			22
			3
			
			2012
		
	




* 
	
		Schwannoma of the Posterior Tibial Nerve Presenting as Tarsal Tunnel Syndrome: A Case Report with Emphasis on the Role of Microscope during Surgery
		
			RajaBhaskara Rajasekaran
		
		
			RajasekaranShanmuganathan
		
		ID 4704362
	
	
		Case Reports in Orthopedics
		
			2018
			4
			2018