15018752330
发表时间:2015-12-08 浏览次数:552次
Introduction
Guyon's canal, named after Felix Guyon, is a fibro-osseous tunnel within the ulnar side of the wrist. [1]
It is bound radially by the hamate, volarly by the volar carpal
ligament, dorsally by the transverse carpal ligament, and ulnarly by the
pisiform and the flexor carpi ulnaris. The ulnar neurovascular bundle
enters the hand through this tunnel. Ulnar nerve compression in this
enclosed space leads to Guyon's canal syndrome, first described by Hunt. [2] The common causes are ganglion, repetitive trauma, vascular lesions, tumors, and anomalous muscles.
Lipoma,
though termed universal tumor due to its ubiquitous presence, is rare
in Guyon's canal. This is probably due to the paucity of adipose tissue
in this fibro-osseous tunnel. There are only 12 previously reported
cases. We report a case of lipoma in the Guyon's canal causing ulnar
neuropathy.
Case report
A 55-year-old male presented with swelling in the left hand with a duration of 3.5 years. He complained of numbness in the ring and little fingers. On examination, a diffuse swelling was noted in the hypothenar area extending from the distal palmar crease to the proximal wrist crease [Figure 1]. The swelling was soft but tense.
Sensory examination recorded diminished sensation over the little finger
and the ulnar half of the ring finger on their volar surfaces. The
patient rated the sensation as three out of ten in the "ten test" ("ten
test" is a semi-quantitative assessment in which the patient ranks the
quality of sensation in the affected digit compared with that in the
normal contralateral digit on a score of 1-10). Sensation on the dorsal
aspect was normal. There was no motor weakness, and the adductor
pollicis, lumbricals, and interossei had normal function.
Magnetic
resonance imaging (MRI) revealed a 6.5 cm × 4 cm × 2.5 cm
well-encapsulated swelling in the hypothenar space extending into
Guyon's canal. The lesion was hyper-intense on T1-weighted and
T2-weighted imaging with suppression of the short T1 inversion recovery
signal, suggestive of lipoma [Figure 2].
Surgical exploration under axillary block with tourniquet control
revealed a well-encapsulated, dumbbell-shaped tumor in the hypothenar
space and Guyon's canal [Figure 3].
The distal sensory branches of the ulnar nerve were firmly adherent to
the tumor and were splayed by it. It appeared as if the branches were
embedded in the tumor capsule. There was inadvertent injury to the ulnar
digital nerve to the little finger, which was repaired with 8-0 nylon.
Postoperative
recovery was uneventful. The histopathological examination showed
mature fat cells, suggestive of lipoma. At 6-month follow-up, the
patient was doing well with normal sensation on the ring and little
fingers.
Discussion
Lipoma in Guyon's canal is rare, with only 13 cases reported, including the present case [Table 1].
Except for the case of an 8 years old, [9]
all others were reported in adults, ranging from 36 to 74 years old,
with a mean age of 52.2 years. There were 7 males and 6 females. Nine of
the 13 cases occurred on the right side. The tumor size varied from 1.5
cm × 1 cm (area) to 6.5 cm × 4 cm × 2.5 cm (volume), with this largest
lesion seen in the present case. Six patients had only sensory
involvement, 2 had only motor symptoms, and 4 patients had a combined
neuropathy. One patient had no neuropathy and was the only pediatric
patient in the series. This was attributed to unique anatomical and
physiological differences for Guyon's canal and the attending nerves. [9]
MRI was taken in 7 cases. It gave accurate diagnosis in 5 patients,
while, in 2 cases, the findings were suggestive of ganglion. [6],[13] Surgical removal alleviated symptoms in all patients.
Shea
and McClain have classified lesions of Guyon's canal into three types:
type I - proximal lesions having both sensory and motor involvement
(30%), type II - lesions causing weakness of the intrinsic muscles (52%)
and type III - distal lesions causing only sensory abnormalities (18%). [14] Recently Wu et al. have suggested a classification into five types. [15]
Type I is a mixed motor and sensory neuropathy with the lesion at the
proximal end of Guyon's canal. Type II is a pure sensory neuropathy,
with the lesion involving only the sensory branch. Type III is a pure
motor neuropathy, with the lesion proximal to the branch supplying the
hypothenar muscles. Type IV spares the hypothenar muscles with the
lesion distal to the hypothenar muscle branch. Type V involves only the
adductor pollicis and first dorsal interosseous muscles. The present
case is type III according to Shea and McClain and type II according to
the Wu classification.
Ganglions are the most common causes of
Guyon's canal syndrome. Other causes include giant cell tumors,
neurilemmomas, repetitive trauma, vascular lesions, anomalous muscles,
carpal fractures and rheumatoid arthritis. Lipoma is a rare cause of
nerve compression at this site.
The cellular origin of lipoma in Guyon's canal is debatable. Balakrishnan et al.[10]
reported a case in which the branches of the ulnar nerve were splayed
by the tumor; these authors postulated that the lipoma originated from
the nerve itself and termed it an "intra neural lipoma". Our case was
similar in presentation. The lipoma was present between the superficial
and deep branches of the ulnar nerve. The superficial sensory branches
were splayed by the tumor and appeared to be embedded in the capsule.
Hence, an intraneural origin cannot be ruled out.
The possibility
of nerve injury should always be discussed with the patient
preoperatively. Extreme caution should be exercised while approaching
these tumors as the nerve fibers may be splayed and embedded in the
capsule. The capsule should be incised in the area least likely to
contain nerve fibers and the tumor carefully enucleated.
It is
difficult to predict whether a tumor in our case grew into Guyon's canal
from the hypothenar space or grew out of Guyon's canal. As tumors grow
in areas of least resistance, it is less likely that the lipoma would
have entered the tight compartment.
References
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14.Shea JD, McClain EJ. Ulnar-nerve compression syndromes at and below the wrist. J Bone Joint Surg Am 1969;51:1095-103.
15.Wu JS, Morris JD, Hogan GR. Ulnar neuropathy at the wrist: case report and review of literature. Arch Phys Med Rehabil 1985;66:785-8.