Keywords nerve compression syndromes - neurilemmoma - peripheral nervous system neoplasms -
radial nerve - radial neuropathy
Introduction
The radial nerve originates from the posterior fascicle of the brachial plexus, innervating
all the posterior compartment muscles of the arm and forearm. Particularly, radial
nerve compression in the proximal region of the forearm can result in posterior interosseous
nerve syndrome, which specifically affects the extensor compartment muscles of the
forearm.[1 ]
However, posterior interosseous syndrome may present different signs and symptoms
with varying degrees of intensity. Therefore, history taking and physical examination
are crucial for its diagnosis, and electroneuromyography is an important complementary
test to confirm diagnosis.
The objective of this report was to describe the symptoms and surgical procedure for
posterior interosseous nerve syndrome caused by a schwannoma (also called neurilemmoma),
which is a type of peripheral nervous system tumor.
Case Report
A 65-year-old female patient, who was a professor of exact sciences, presented with
a chief complaint of pain at the end of the day, which worsened with the loss of extension
movement in the third, fourth, and fifth fingers of her left hand. This condition
progressed for 2 months and was associated with sporadic paresthesia in the dorsum
of the left hand and forearm. On physical examination, she reported pain on palpation
of the proximal and radial third of the left forearm adjacent to the radial head;
however, no tumor mass was palpated or observed. A radiography was requested for differential
diagnosis without showing abnormalities.
Posterior interosseous nerve syndrome was then diagnosed on electroneuromyography,
and a surgical procedure was performed. The patient was asked if data concerning the
case could be submitted for publication, and she consented.
During the surgical procedure, an incision of ∼ 10 cm was made in the proximal radial
third of the left forearm, wherein strangulation of the posterior interosseous nerve
at the arcade of Frohse was visualized due to the presence of a 3-cm3 fibroelastic tumor. The mass was then removed, subsequently decompressing the posterior
interosseous nerve ([Fig. 1 ] - A, B, C, D, E, and F). After 6 months and with the help of physical therapy, the
patient presented with full motor recovery of her left-hand fingers.
Fig. 1 (A ) Intraoperative photographs of the anterior forearm approach. (B ) The tumor involving the posterior interosseous nerve. (C ) Tumour resection. (D and E ) The tumor and its cross-section demonstrating fibroelastic and yellowish characteristics.
(F ) An anatomopathological image showing spindle-shaped cells, with a concentration
of deformed and undulated nuclei as sparse mitoses, which point to a diagnosis of
schwannoma.
Discussion
The radial nerve exits the posterior trunk of the brachial plexus, dividing itself
into the superficial (sensory) and deep (motor) branches in the proximal forearm,
which then innervate all the muscles of the posterior compartment of the forearm.[2 ]
In particular, posterior interosseous nerve syndrome can result from trauma; expansive lesions, such as tumors ; local nerve inflammation, such as rheumatoid arthritis; and nonspecific brachial
neuritis. Notably, cases of posterior interosseous nerve compression secondary to
schwannoma or neurilemmoma are rare, with only a few cases being reported in the literature.
Despite being the most common benign tumor of the peripheral nerve sheath, it accounts
for only 5% of soft-tissue tumors, with a high incidence in the head and neck. Furthermore,
in cases when a schwannoma affects the upper limbs, it has been reported to prefer
the anterior surface of the forearm due to the high concentration of nerve fibers,
of which the ulnar and median nerves are the most affected.[3 ]
In the case of this patient, radiography was requested for differential diagnosis,
and electroneuromyography for confirmation. As there was no palpable mass, imaging
tests such as ultrasound (US) or magnetic resonance imaging (MRI) were not requested,
since the motor alteration was already triggered. However, some authors, such as Galbiatti
et al.[3 ] and Wheeler and DeCastro[4 ] believe that, although the clinical examination is paramount, an image exam such
as US or MRI should be requested for differential diagnosis of soft tissues.
Such patients may present with weakness in finger extension, and the wrist may deviate
radially due to the weakness of the extensor carpi ulnaris muscle. Depending on its
severity, a positive digit-digital percussion sign at the site of the lesion can also
be elicited.[5 ]
The initial treatment for posterior interosseous nerve syndrome is conservative, including
wrist splinting, anti-inflammatory and analgesic therapy, physical therapy, and daily
activity changes.[4 ]
Surgical treatment is only reserved for cases refractory to conservative management
for at least 3 months. Surgical decompression for posterior interosseous nerve syndrome
focuses on releasing the areas of compression, including the fibrous bands superficial
to the radiocapitelar joint, fibrous border of the extensor carpi radialis brevis,
the arcade of Frohse, and the distal border of the supinator.[4 ] In this case, as there were already motor signs and symptoms, a surgical treatment
was immediately chosen. Following surgery, the patient underwent physical therapy,
recovering left-hand motor patterns in 6 months ([Fig. 2 ]).
Fig. 2 The late postoperative period, after 6 months of physical therapy. (A, B , and C ) Images showing wrist and finger extension recovery. (D and E ) Photograph of the surgical incision site and its healing.
