Accepted Manuscript

Letter to the Editor

Peripheral nerve tumors associated with Martin-Gruber anastomosis

C. Erra, D. Coraci, P. De Franco, G. Granata, L. Padua

PII: S1388-2457(14)00294-6DOI: http://dx.doi.org/10.1016/j.clinph.2014.05.019Reference: CLINPH 2007116

To appear in: Clinical Neurophysiology

Accepted Date: 14 May 2014

Please cite this article as: Erra, C., Coraci, D., De Franco, P., Granata, G., Padua, L., Peripheral nerve tumorsassociated with Martin-Gruber anastomosis, Clinical Neurophysiology (2014), doi: http://dx.doi.org/10.1016/j.clinph.2014.05.019

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Peripheral nerve tumors associated with Martin-Gruber anastomosis

C. Erra a, D. Coraci

b, P. De Franco

c, G. Granata

a, L. Padua

a,b

a Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy

b Board of Physical Medicine and Rehabilitation, Department of Orthopedic Science, “Sapienza”

University, Rome, Italy

c Don Carlo Gnocchi Foundation, Milan, Italy

Corresponding author:

Carmen Erra

Institute of Neurology, Catholic University of Sacred Heart, Largo A. Gemelli 8, 00168 Rome, Italy

Tel: +39 06 3015 6623

Fax: +39 06 3550 1909

E-mail: carmen.erra@hotmail.it

Introduction

Anomalous communications between median and ulnar nerve in the forearm have been widely

described during the years. The most common of these anastomosis, known as Martin-Gruber

anastomosis (MGA), consists in a neural connection between median and ulnar nerve in the

forearm, usually in its proximal part, that results in an anomalous course of the fibers innervating

the intrinsic muscles (and rarely cutaneous region) of the hand.

Its frequency, firstly described by Gruber in 1870 as 15.2% in 250 studied arms, is currently

estimated through neurophysiological and anatomical studies to range between 10% and 40%

(Amoiridis, 1992; Rodriguez-Niedenführ et al., 2002; Lee et al., 2005). Much rarer is ulnar to

median communication, known as Marinacci communication, where fibers from the ulnar nerve

cross over to the median nerve in the forearm (Marinacci, 1964).

The knowledge of such anatomical variants is important to explain some electrodiagnostic (EDX)

findings. Moreover, its identification is crucial for reaching a correct diagnosis and providing

information on prognosis and treatment.

We report on two patients who presented with the coexistence of median-ulnar anastomosis

and nerve tumors.

Patient 1

A 69-year-old man came to our attention for left hand weakness and sensory loss. The patient was a

trumpeter and had increasing difficulties in playing the trumpet. Physical examination showed

hypoesthesia at the first two fingers of his left hand. Deep tendon reflexes were normal. At the

proximal third of the arm, on the lateral aspect, a small mass was palpable.

Nerve conduction studies were consistent with the presence of MGA: in particular stimulating the

left ulnar nerve at the wrist and recording from abductor digiti minimi (ADM) a compound motor

action potential (CMAP) amplitude of 7.4 mV was obtained, while stimulating the same nerve

above and below elbow a CMAP amplitude of 5.3 mV was recorded. No response was elicitable

stimulating the left median nerve at the wrist and recording from ADM, while stimulating the same

nerve at elbow a CMAP amplitude of 1.9 mV was obtained (Fig. 1a).

US evaluation of the median nerve showed, at the proximal third of the arm, the presence of an

ovular hypo/isoechoic shaped formation, in continuity with the nerve (length on longitudinal view

2.75 cm) (Fig. 1b) suggestive of a median nerve schwannoma. Based on EDX and US findings, we

inferred that the tumor likely involved both median nerve fibers and the ulnar nerve fibers involved

in the anastomosis (Fig. 1c).

Patient 2

A 22- year- old woman developed paresthesias in the first three fingers of her right hand. Physical

examination showed mild weakness of median intrinsic hand muscles and thenar hypotrophy. Deep

tendon reflexes were normal. EDX testing suggested the presence of median-ulnar anastomosis in

the arm (Fig. 1d): stimulating the right ulnar nerve at the wrist and recording from ADM a CMAP

amplitude of 12.0 mV was obtained, while stimulating the nerve below and above elbow the CMAP

amplitude was 8.7 and 8.4 mV, respectively. Stimulating the right median nerve at the wrist and

recording from the ADM there was no response, while stimulating the same nerve at the elbow we

obtained a CMAP amplitude of 3.0 mV. Stimulating the right median nerve at the wrist and

recording from abductor pollicis brevis (APB) we obtained a CMAP of 4.8 mV, while stimulating

the nerve above the elbow we obtained a response of 10.3 mV. Finally stimulating the ulnar nerve

at the wrist and recording from the APB we obtained a CMAP of 5.9 mV, as if some fibers to the

APB were routed through the ulnar nerve. Moreover, a slight amplitude reduction of the median

sensory response was seen. US of the median nerve showed, at the proximal third of the arm, severe

focal nerve enlargement with no homogenous echogenicity, suggesting the presence of a

neurofibroma (Fig. 1e). The patient underwent surgery where complete tumor resection and sural

nerve graft were performed. Immediately after surgery, although the interruption of the median

nerve, the patient partially recovered function of median innervated hand muscles. EDX performed

recording from APB and stimulating the right median nerve at the wrist showed no response while

stimulating the same nerve at the elbow and the right ulnar nerve at wrist a CMAP of 5 mV was

recorded. This observations suggested that at least some median nerve fibers were spared, and this

could be due to the anastomosis (Fig. 1f).

Discussion

In both these patients we found the coexistence of peripheral nerve tumors and median-ulnar

anastomosis, but the clinical implications were opposite in the two cases.

In the first case, because of the anastomosis, both median and ulnar nerve fibers were at risk for

injury from surgical exploration. For the surgical risk and the professional activity (trumpet player),

the patients decided not to undergo surgery and is regularly followed-up at out lab.

In the second case, the anastomosis-tumor combination resulted in potential benefit for the patient

in that the MGA assured that some median nerve fibers were spared from the tumor and its

resection allowing for retention of median nerve function. Through these cases we want to

underline how an accurate combination of EDX and US assessment may be crucial for therapeutic

decision and patient outcome.

References

Amoiridis G. Median--ulnar nerve communications and anomalous innervation of the intrinsic hand

muscles: an electrophysiological study. Muscle Nerve 1992; 15:576-579.

Lee KS, Oh CS, Chung IH, Sunwoo IN. An anatomic study of the Martin-Gruber anastomosis:

electrodiagnostic implications. Muscle Nerve 2005.31:95-97.

Marinacci AA. The Problem Of Unusual Anomalous Innervation Of Hand Muscles. The Value Of

Electrodiagnosis In Its Evaluation. Bull Los Angel Neuro Soc 1964. 29:133-142.

Rodriguez-Niedenführ M, Vazquez T, Parkin I, Logan B, Sañudo JR. Martin-Gruber anastomosis

revisited. Clin Anat 2002. 15:129-134.

Figure Legend

Figure 1. (a) Motor Nerve Conduction Studies of patient 1. (b) Median nerve ultrasound,

longitudinal section: nerve schwannoma (S), with some speared fascicles (arrows). (c) Schematic

representation of nerve anastomosis and tumor location. (d) Motor Nerve Conduction Studies of

patient 2. (e) Median nerve ultrasound, transversal section: nerve neurofibroma (N, arrows). (f)

Schematic representation of nerve anastomosis and tumor location.

M: median nerve (continuous line), U: ulnar nerve (dotted line), ADM: abductor digiti minimi,

APB: abductor pollicis brevis, T: tumor, *: Martin-Gruber anastomosis, §: m. biceps brachii, # :

brachial artery.

Fig. 1.