Background
The two most common nerve tumours in the upper extremity are Schwannoma and neurofibroma
[[1],[2]]. More rare is a fibrolipomatous hamartoma, a benign, slow-growing mass, which is
usually located in the median nerve distally in the forearm [[3],[4],[5],[6],[7]] and in its digital branches [[1],[4],[5]]. With MR imaging it is not always possible to make a diagnosis of a nerve tumour
[[2]], but the MR imaging characteristics of fibrolipomatous hamartoma are considered
to be pathognomonic [[3]]. In coronal plane, the nerve tumour is characterised by serpiginous structures
[[4],[6]] (thickened nerve fascicles), which are surrounded by fat (high signal intensity
on T1-weighted images, low signal intensity on fat-suppressed T2-weighted images)
[[3]]. In most of the cases the fat is distributed between the nerve fascicles making
the nerve tumour looking like a coaxial cable in the axial plane [[3],[4],[5],[8],[9]]. Even if the nerve tumour has a characteristic feature on MRI the suspicion of
a nerve tumour is not always obvious for the clinician. Here we report a case with
obscure clinical symptoms and signs of isolated median nerve dysfunction, where the
MR imaging showed the characteristic features of a fibrolipomatous hamartoma in the
arm and the diagnosis was verified by an incisional biopsy.
Case presentation
A 57 year right-handed secretary was referred to our hospital July 2008. She described
symptoms since November 2002 with paresthesia in the right index, long and ring (half
of it) fingers. Furthermore, she told about fibrillations in the interphalangeal joint
of the right thumb and the index finger, loss of FPL and FDP function to the index
finger followed by atrophy of the thenar muscles a year later. She was operated with
carpal tunnel release at another hospital April 2007 due to a suspicion of a carpal
tunnel syndrome, but no neurography or electromyography (EMG) was performed. In addition,
she was operated with division of the A1 pulley on the right thumb due to a suspicion
of a right-sided trigger thumb, but with no improvement. In February 2008, after the
carpal tunnel release, neurography and EMG were performed. These investigations showed
a severe loss of nerve fibres, but with remaining nerve fibers, in the right median
nerve. Electrophysiologically, signs of reinnervation were seen, but no nerve compression
lesion was found.
At the clinical examination in July 2008 at our hospital she had atrophy of the thenar
muscles and clear signs of affection of the anterior interosseous nerve with impaired
function of the FDP to the index finger and FPL and decreased grip strength. She described
a slight pain at palpation in the middle part of the forearm along the median nerve.
She had paraesthesia located only in the long finger. The circumference of the right
arm was 1.5 cm shorter than the left forearm indicating atrophy of some of the forearm
muscles. She had no other clinical or neurographical signs of motor or sensory dysfunction.
There was no obvious cause of the longstanding, severe nerve fibre loss in the median
nerve. An MRI was performed of the right median nerve at axilla level and distally.
The MRI showed a median nerve with serpiginous appearance. Single nerve fascicles
in a well defined tissue mass containing fat was found ([Figure 1]). The condition extended from the proximal humerus to the wrist and thereafter the
median nerve had a normal appearance. The diameter of the tumour was 1.7-2.5 cm. Due
to the typical MRI changes ([Figure 1]) the diagnosis was suggested as a fibrolipomatous hamartoma of the median nerve.
An incisional biopsy after exploration of the median nerve was done in February 2009
under microscopical dissection. The median nerve had a diameter up to 2 cm and there
were no adhesions to the surrounding tissue. The macroscopical appearance of the nerve
tumour indicated a fibrolipomatous hamartoma ([Figure 2]) and five incisional biopsies were taken from representative areas. Neurolysis of
the median nerve was done from the middle part of the arm down to the middle part
of the forearm. Microscopy showed a fibrolipomatous tissue that surrounded and splayed
apart the peripheral nervous tissue, which was also fibrotic and atrophic ([Figure 3]). The postoperative follow-up was uneventful. She returned to her original profession.
She still has dysfunction of the FPL, and thenar atrophy although she can do an opposition
of the thumb. She felt some improvement after the exploration and neurolysis of the
nerve around the elbow. A tendon transfer procedure may be considered in the future.
She is followed regularly with particularly clinical examinations.
Figure 1 Magnetic resonance investigation (MRI) of the patient showing specific characteristics
of a fibrolipomatous hamartoma (arrows) in sagittal sections (T1 weighted in A and
B) and in axial sections (T1-weighted in C and D; T2-weighted in E and F) at the elbow
region.
Figure 2 At exploration of the median nerve at the elbow region a thickened nerve
(arrows in A) was shown where the incisional biopsy showed a fibrolipomatous hamartoma
(see Figure 3). Close up of the condition in B.
Figure 3 Microscopical pictures of sections from the incisional biopsy showing (A)
fibrolipomatous tissue with few atrophic peripheral nerve fascicles and fibrotic tissue
(HE; × 10) and (B) atrophic and fibrotic nerve fibers stained with S-100 immunohistochemical
staining (S-100; × 20).
Discussion
Of all tumours in the upper extremity, 2% are nerve tumours [[10]]. Schwannoma is probably the most frequent one with a known incidence of less than
1/100000 inhabitants and year in Sweden [[1]]. Usually, the diagnosis of a nerve tumour has to be based on microscopical findings
since MRI is not sufficient for a precise diagnosis [[2]]. In contrast, a fibrolipomatous hamartoma, which is even more rare, has very distinct
characteristics in MRI with serpiginous hypotense structures representing thickened
fascicles which are surrounded by evenly distributed fat [[4]] (high T1-weighted signal intensity and low fat-suppressed T2-weighted signal intensity)
[[3],[4],[6]]. Our case showed such MRI characteristics and, furthermore, the diagnosis was confirmed
by microscopy. We did not perform any ultrasound examination of the patient due to
the lack of palpable tumour before exploration. However, such an investigation may
be considered when there is a suspicion of a nerve tumour, although MRI is frequently
used [[2]].
The origin of fibrolipomatous hamartoma is still obscure and is mainly affecting and
found in young persons [[4],[5],[6],[7]]. That might indicate a congenital aetiology [[7]], although a few cases have been reported in older people as seen here. Another
theory is that the lesion can be caused by trauma [[3],[4],[5]]. There are debates of the relationship between fibrolipomatous hamartoma and macrodactyli
[[3],[4],[5],[7]]. However, our patient had no signs of this clinical presentation.
Our patient had a long history with motor disturbances, such as thenar atrophy and
loss of FPL function. Most cases present with a longstanding painless mass. Nerve
compression of the affected nerve with paresthesia, motor deficit and pain are known
late symptoms [[4],[5],[7],[11],[12],[13],[14]]. It is suggested that it may become symptomatic only in the median nerve due to
encroachment by the flexor retinaculum; thus causing carpal tunnel syndrome [[4],[5]]. However, in our case the tumour was located more proximally extending from the
upper arm almost down to wrist level; thus, presenting a more proximal located fibrolipomatous
hamartoma than previously described. A hypothesis could be that you rarely find these
fibrolipomatous hamartoma more proximal because of spatial relations.
Only a limited number of cases of fibrolipomatous hamartoma are reported in the literature
showing the uncertainty of the optimal treatment suggestion and that treatment should
be guided by the severity of symptoms [[5],[15]]. Our case was treated only by exploration and release of potential narrowing structures,
particularly around the elbow, which improved her symptoms, but excision of the tumour
is not recommendable [[3],[4],[5],[6],[7],[16],[17]]. Due to the extensive fatty infiltration of the nerve fascicles, surgical excision
may cause catastrophic motor and sensory deficits. We performed five incisional biopsies
from different locations to be sure of adequate material for the neuropathological
examination. When an incisional biopsy is gently performed it is our experience that
no further dysfunction is added to the patient. We will follow our patient regarding
any progression of the tumour and further consider additional treatment, such as tendon
transfers, for the impaired function of FPL and FDP to the index finger. However,
the long-term results are obscure of fibrolipomatous hamartoma. Meticulous information
to the patient and a regular follow-up are recommended.
The present case emphasizes the need for a thorough history from the patient and a
careful and meticulous clinical examination of cases with symptoms from the peripheral
nervous system. For example, a nerve tumour can be the cause of symptoms as the present
case. A MRI may reveal a nerve structure with a coaxial-cable-like appearance; thus
with a high suspicion of the diagnosis of fibrolipomatous hamartoma.
Conclusions
Although history of patients with symptoms from the peripheral nervous system as well
as a meticulous clinical examination is recommended, an MRI is an additional tool
to reveal a fibrolipomatous hamartoma at an unusual location.
Consent
Written informed consent was obtained from the patient for publication of this case
report and any accompanying images. A copy of the written consent is available for
review by the Editor-in-Chief of this journal.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
The medical students JN and KS and senior author LD have done literature review and
written the draft of the manuscript. The patient was operated by NSN (senior author)
and NV (nurse; literature review). MRI was performed by LL and the microscopical examination
by EB. All authors have contributed in different important ways to the present manuscript.
All authors have read and approved the final manuscript.
Cite this article as: Nilsson et al.: Fibrolipomatous hamartoma in the median nerve in the arm - an unusual location but
with MR imaging characteristics: a case report. Journal of Brachial Plexus and Peripheral Nerve Injury 2010 5:1.
