Unusual presentation of extensor digitorum brevis manus: Two cases report

Since it was first described by Albinus in 1734, the extensor digitorum brevis manus muscle (EDBM) has been considered an anatomic variant of the finger extensor muscle. Furthermore, cadaveric dissections have shown that it is present in approximately 2–3% of the population (Ogura et al., 1987; Rodriguez-Niedenfuhr et al., 2002). This anomalous muscle originates at the dorsal wrist joint capsule and most commonly inserts in the index finger (Rodriguez-Niedenfuhr et al., 2002). Awareness of the existence of the EDBM is important when making a differential diagnosis and considering the treatment of mass lesions with similar appearances. Magnetic resonance imaging (MRI) and ultrasonography have been reported to be useful for differentiating suspected EDBM and pathologic soft tissue masses, and thus, for avoiding unnecessary surgery (Cigali et al., 2002; Ouellette et al., 2003). Unusually, EDBM is symptomatic, particularly in young workers that use their hands for repetitive motions over long periods of time (Kuschner et al., 1989). Dorsal wrist swelling with pain can be caused by an EDBM, but these symptoms are frequently misdiagnosed as a dorsal wrist ganglion, nodular tenosynovitis, synovial cyst, or a benign soft tissue tumor (Rodriguez-Niedenfuhr et al., 2002). One anatomic study reported on the incidence and characteristic appearance of this muscle (Ranade et al., 2008). However, clinically accurate diagnosis can be difficult, and many cases are identified incidentally during surgery undertaken for the treatment of other diseases around the dorsal wrist. In this report, we describe two unusual EDBMs that were misconceived as a wrist ganglion or a soft tissue tumor, respectively; however, surgery clearly confirmed an unexpected EDBM in both cases. To the best of our knowledge, few clinical cases of an intramuscular ganglion of EDBM or of gigantic EDBM have been previously reported. CASE REPORTS