Casi Clinici

Chirurgia della Mano - Vol. 51 (2) 2014

SCHWANNOMA OF THE ANTERIOR INTEROSSEOUS NERVE: A CASE REPORT

Roberto Adani*, Luigi Tarallo**, Stefano Colopi***, Raffaele Mugnai*

* Department of Hand Surgery and Microsurgery, University Hospital of Verona, Verona, Italy ** Department of Orthopedics, University Hospital of Modena, University of Modena and Reggio Emilia, Modena, Italy *** Department of Radiology, University Hospital of Modena, University of Modena and Reggio Emilia, Modena

Referente Roberto Adani Piazzale La Scuro, 10 Verona - E-mail: [email protected]

SCHWANNOMA OF THE ANTERIOR INTEROSSEOUS NERVE: A CASE REPORT

SINTESI

Gli Schwannomi sono i tumori più frequenti dei nervi periferici. Il coinvolgimento del nervo interosseo anteriore (AIN) è piuttosto insolito, a differenza del nervo mediano che è uno dei più interessati. Per la loro bassa incidenza in questo distretto, i segni clinici ed i sintomi di questi tumori possono portare talvolta a diagnosi erronee (i.e. altri tumori dei tessuti molli, in particolare gangli o tenosinoviti). Presen tiamo il caso di un atleta di 27 anni, praticante judo a livello agonistico, e giunto all’ osservazione per la comparsa di un dolore presente al momento in cui veniva afferrato al polso durante l’attività sportiva. La RMN con contrasto ha mostrato la presenza di una massa ovalare (12x10x9mm) a livello del fascio vascolo-nervoso anteriore ed in contiguità con il muscolo pronatore quadrato. L’esame istopatologico ha confermato la diagnosi di Schwannoma. Un mese dopo l’asportazione chirurgica del tumore il paziente ha ripreso l’attività sportiva agonistica. In conclusione la diagnosi di Schwannoma dell’AIN può risultare non semplice, per questo motivo è necessario un attento esame clinico per ricercare i segni clinici tipici dello Schwannoma, in particolare il segno di Tinel.

Parole chiave: Schwannoma, neurilemmoma, nervo interosseo anteriore

SUMMARY

Schwannomas are the most common tumours of the peripheral nerves. While the median nerve is one of the most affected, the involvement of the anterior interosseous nerve (AIN) is rather unusual. Because of this low incidence, the clinical signs and symptoms are often misunderstood, and somehow associated to other soft tissue tumors such as gangliomas, or to a tenosynovitis. We describe a case of a 27-year-old man that practised judo at competitive level and reported pain when his forearm was grasped distally during sport activity. MRI with contrast showed an oval mass (12x10x9 mm) in correspondence of the neurovascular anterior interosseous bundle. Histopathologic examination revealed it to be a schwanno ma. One month after surgery, the patient returned to normal sport activity. Diagnosis of AIN schwannoma is not simple: specific clinical signs only appear when the tumour is located proximally. For these reasons a meticulous clinical examination should search for typical signs of schwannomas such as a positive Tinel sign.

Keywords: neurilemmoma, schwannoma, anterior interosseous nerve

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Roberto Adani, Luigi Tarallo, Stefano Colopi, Raffaele Mugnai

Chirurgia della Mano - Vol. 51 (2) 2014

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INTRODUCTION

Schwannoma is a benign tumor developing from Schwann cells. In 95% of cases those tumors present as an isolated mass [1], and they are characterized by a slow and non infiltrating pattern of growth. The tumor is often associated to a “tingling sensation”, which is not constant at clinical evaluation. The in cidence of Schwannoma in eastern countries is 5% in adults and 2% in children [2]. Because of this low incidence, the clinical signs and symptoms are of ten misunderstood, and somehow associated to other soft tissue tumors such as gangliomas, or to a teno synovitis [3]. Hems et al. reviewed a series of 104 peripheral-nerve benign tumors, and demonstrated that in only 7 cases the preoperative diagnosis was accurate [4].

CASE REPORT

The patient gave informed consent to participate and was informed that data concerning the case would be submitted for publication. This report was performed in accordance with the Ethical standards of the 1964 Declaration of Helsinki as revised in 2000.

A 27-year-old right handed man was observed for persistent discomfort (six months) in the volar region of the left wrist following external pressure. The pa tient practised judo at competitive level and reported pain when his forearm was grasped distally during sport activity. On examination there was no visible external swelling, but on deep palpation a firm and slightly tender mass could be felt in the soft tissues over the palmar region of the distal third of the left forearm. The Tinel sign was partially positive. The re was no muscle weakness and no sensory deficit. High-resolution sonography identified a well-defined hypoechoic mass along the anterior interosseous ner ve (AIN) at the distal forearm (Fig. 1). MRI was per formed to better define the origin of the mass and to show its relation to surrounding structures.

MRI with gadolinium contrast showed at the distal third of the forearm an oval mass (12x10x9 mm) in correspondence of the neurovascular anterior in terosseous bundle and in contact with the pronator quadratus muscle. The mass was isointense on T1 weighted images, hyperintense on T2-weighted ima ges and characterized by significant contrastographic impregnation (Fig. 1). Surgery was performed under loupe magnification employing the Henry volar ap proach. The pronator quadratus muscle was incised on the radial border revealing a yellowish, smooth, oval mass connected to the AIN (Fig. 2). The mass presented two small pedicles both originating from the AIN. Resection of the tumour was completed wi thout the need to reconstruct the small nerve fascicle involved. Histopathologic examination revealed it to be a schwannoma. One month after surgery, the pa tient returned to normal sport activity. At 12 months follow up there was no evidence of recurrence and the patient was free of symptoms.

DISCUSSION

Schwannomas are the most common tumours of the peripheral nerves. Neurilemmomas are slow growing, soft in consistency, mobile in nature, and sometimes painless. They are often misdiagnosed as lipomas, fibromas, ganglion, or xanthoma [6]. Sch wannomas are usually localized on the volar surface of the limb due to the higher concentration of nerve fibres. �hile the median nerve is one of the most affected [7], the involvement of the AIN is rather unusual [8,9]. Diagnosis of AIN schwannoma is not simple: specific clinical signs only appear when the tumour is located proximally. For these reasons a meticulous clinical examination should search for typical signs of schwannomas such as a positive Ti nel sign and peripheral paresthesias.

US examination may be very helpful although it cannot always reveal the connection of the tumour

* *

Figure 1. Axial view

of the Ultrasound and MRI (SE T2 weighed) showing the schwan noma (*) under the pronator quadratus muscle (°).

Schwannoma of the Anterior Interosseous Nerve: a Case Report

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Chirurgia della Mano - Vol. 51 (2) 2014

Figure 2. Intraoperative view of the schwannoma

under the pronator quadratus muscle connected to the AIN (*).

with the nerve. MRI is considered the gold standard to identify the dimension of the tumour, to define its origin, and to show the neurovascular structures involved [5]. However with MRI it’s not possible to distinguish between schwannomas and neurofi bromas in all cases. Resection of the schwannoma should be performed carefully in order to preserve as much nerve as possible. When approaching a palpable mass in the upper limbs, the presence of a peripheral nerve tumour should also be considered.

REFERENCES

1. Takase K, Yamamoto K, Imakiire A. Clinical pa thology and therapeutic results of neurilemmo ma in the upper extremity. J Orthop Surg 2004; 12: 222-5.

2. Forthman CL, Blazar PE. Nerve tumors of the hand and upper extremity. Hand Clin 2004; 20: 233-42.

3. Rockwell GM, Thoma A, Salama S. Schwanno ma of the hand and wrist. Plast Reconstr Surg 2003; 3: 1227-32.

4. Hems TEJ, Burge PD, Wilson DJ. The role of magnetic resonance imaging in the management of peripheral nerve tumors. J Hand Surg Br 1997; 22: 57-60.

5. Adani R, Baccarani A, Guidi E, Tarallo L. Sch wannomas of the upper extremity: diagnosis and treatment. Chir Organ Mov 2008; 92: 85-8.

6. Sandberg K, Nilsson J, Søe Nielsen N, Dahlin LB. Tumors of peripheral nerves in the upper ex tremity: a 22-year epidemiological study. Scand J Plast Reconstr Surg Hand Surg 2009; 43: 43-9.

7. Rockwell GM, Thoma A, Salama S. Schwanno ma of the hand and wrist. Plast Reconstr Surg 2003; 111: 1227-32.

8. Ritt MJPF, Bos KE. A very large neurilemmoma of the anterior interosseous nerve. J Hand Surg Br 1991; 16: 98-100.

9. Inukai T, Uchida K, Baba H. A large neurinoma originating from the anterior interosseous nerve. Hand Surg 2002; 17: 375-7.

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Roberto Adani, Luigi Tarallo, Stefano Colopi, Raffaele Mugnai