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Does the 10-MHz transvaginal transducer improve the diagnostic certainty that an intrauterine fluid collection is a true gestational sac

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Review
Sonographic Appearances of Nerve Tumors
Ian Beggs, FRCR
Department of Clinical Radiology, Royal Infirmary, Lauriston Place, Edinburgh, EH3 9YW, United Kingdom
Received 2 February 1999; accepted 24 May 1999
ABSTRACT: This article reviews the clinical and sonographic features of neurilemoma, neurofibroma, intraneural ganglion, traumatic neuroma, and Morton’s
neuroma. The sonographic characteristics and location at typical sites are important diagnostic features for nerve tumors. © 1999 John Wiley & Sons,
Inc. J Clin Ultrasound 27:363–368, 1999.
Keywords: ultrasonography; nerve tumors; neurilemoma; neurofibroma; intraneural ganglion; traumatic
neuroma; Morton’s neuroma
M
any nerve tumors have characteristic sites
and clinical presentations. Sonographic
demonstration of a typical mass in a typical location is for practical purposes often diagnostic. The
sonographic characteristics can also distinguish
between neurilemoma and neurofibroma, 2 common nerve tumors. This article reviews the sonographic characteristics of several common nerve
tumors.
NEURILEMOMA AND NEUROFIBROMA
Neurilemoma and neurofibroma are benign nerve
tumors that are derived from the Schwann cells.1
These tumors will be considered together, although they are distinct lesions. Differences and
similarities will be discussed.
Neurilemoma (also known as schwannoma,
neurinoma, and perineural fibroblastoma) typically presents in middle age as a solitary slowgrowing mass. The tumor is not associated with
neurofibromatosis type 1 (NF1, von Recklinghausen’s disease). Common sites include spinal roots
and major peripheral nerves. Many neurilemomas are asymptomatic. Malignant transformation is rare. Important features of neurilemoma
Correspondence to: I. Beggs
© 1999 John Wiley & Sons, Inc.
VOL. 27, NO. 7, SEPTEMBER 1999
CCC 0091-2751/99/070363-06
include the presence of a capsule, the eccentric
position of the nerve relative to the tumor mass,
and cavitation.1
Solitary neurofibroma (which is not associated
with NF1) and localized neurofibroma (which is
associated with NF1) are histologically indistinguishable. A neurofibroma has no capsule, the
nerve runs through the center of the mass, and
cavitation is rare. Solitary neurofibroma is usually superficial and manifests slightly earlier
than neurilemoma but is otherwise similar in presentation to neurilemoma. The localized neurofibromas of NF1 are multiple, usually appear in
adolescence, and have a 2% risk of malignant
transformation,1 which usually manifests with a
painful, enlarging mass.
On sonography, neurilemoma and neurofibroma are usually well-defined, solid, hypoechoic
soft tissue masses and have faint distal acoustic enhancement (Figure 1).2–13 These tumors
may be indistinguishable from other soft tissue
masses. Occasionally, a neurilemoma or neurofibroma has a coarse echotexture (Figure 2) or contains discrete focal areas (Figure 3) of increased
echogenicity. Histologic examination suggests
that the echogenic areas are due to collagen deposits. The presence of a complete or incomplete
echogenic ring (Figure 4) within the substance of
a mass is a rare but virtually pathognomonic feature of nerve tumors.14 Demonstration of the
nerve (Figure 5) running into the mass is also
diagnostic of nerve tumors. Thickening and loss of
anisotropy may produce a hypoechoic rather than
hyperechoic appearance.12,13 The position of the
nerve relative to the mass distinguishes between
neurilemoma (nerve at periphery of mass) and
neurofibroma (nerve running into center of mass;
Figure 5), although it is not always possible to
identify the nerve. An echogenic capsule (Figure 6) is usually seen in neurilemoma but is rare
363
BEGGS
FIGURE 1. Neurilemoma. Longitudinal sonogram of the lower leg
shows a well-defined, homogeneous, hypoechoic mass and distal
acoustic enhancement. The mass is a neurilemoma lying within the
anterior tibial muscle. This image and all others were obtained with a
128XP ultrasound scanner (Acuson, Mountain View, CA) and a 7.5MHz linear-array transducer.
in neurofibroma. Cystic spaces (Figure 7) are
typical of a degenerated neurilemoma or “ancient
schwannoma.” Increased blood flow on color
Doppler imaging has been reported in neurilemoma (Figure 8) but not neurofibroma, although
I have seen it in both types of tumors.12,13 Vascularity may help to distinguish a nerve tumor from
a lymph node.12
Many nerve tumors present as asymptomatic
masses or as small, palpable masses that are
painful when knocked. A small minority of patients with nerve tumors present with recurrent
episodes of severe lancinating pain that may require opiate analgesia. Clinical examination may
be unremarkable, and episodes of pain may be
months apart, leading to delays in clinical diagnosis. When the diagnosis is suspected, Doppler
sonography can usually provide confirmation.9
The neurovascular bundle is easily followed and
the adjacent mass identified (Figure 4). However,
not all nerves run in a neurovascular bundle. The
sciatic nerve is the obvious example. Diagnosis of
a nerve tumor should be made only when confirmatory clinical evidence is present. An enlarged
lymph node or thrombosed aneurysm could have
similar sonographic appearances. However, a
thrombosed aneurysm will bleed if incised, even if
it lacks Doppler signals.
Variants of neurofibroma include diffuse and
plexiform neurofibromas. These variants have no
specific ultrasound features and are better imaged by MRI. However, sonography can show a
lamellar pattern and increased blood flow in dif364
FIGURE 2. Neurilemoma. Transverse sonogram of the flexor compartment of the forearm shows a coarsely echogenic neurilemoma.
fuse neurofibroma,15 and plexiform neurofibroma
may be multinodular.16
Sonography can be used to guide biopsy of soft
tissue masses. This may be of particular value in
the patient with known NF1 who develops a painful, enlarging mass. Caution should be exercised
before performing ultrasound-guided biopsy.
Staging should be complete, and the appropriate
tumor surgeon should know about the biopsy and
the proposed biopsy route so that subsequent surgery will not be compromised. Few pathologists
will offer a diagnosis of a soft tissue mass from a
fine-needle aspirate, and most will require a
larger sample taken with a cutting needle. Postbiopsy bleeding may make the nerve and tumor
more adherent and difficult to separate. Large,
asymptomatic masses offer easy targets that can
be biopsied with a needle painlessly. Small, symptomatic tumors are excruciatingly painful to biopsy with a needle and can in any case be removed easily by excisional biopsy.
INTRANEURAL GANGLION
Intraneural ganglia occur typically at the knee
but are occasionally reported elsewhere. The ganJOURNAL OF CLINICAL ULTRASOUND
NERVE TUMORS
FIGURE 5. Neurofibroma. Longitudinal sonogram of the flexor compartment of the forearm shows the central position of the median
nerve (arrows) running into the mass. This finding indicates neurofibroma.
FIGURE 3. Neurofibroma. Transverse sonogram of the flexor compartment of the forearm shows a mostly hypoechoic neurofibroma
(arrows). The round echogenic area within the tumor is due to collagen deposition.
FIGURE 4. Neurofibroma. Longitudinal sonogram of the upper arm
shows a neurofibroma that is lying alongside a blood vessel and that
contains an echogenic ring. The ring lies within the tumor mass, not
at the periphery.
glion emerges from the proximal tibiofibular joint
and invades the common peroneal/external
popliteal nerve or 1 of its branches. Patients present with pain, paresthesia, swelling, and weakness, singly or in combination. Sonography shows
a typical ganglion (Figure 9): a usually welldefined, encapsulated, multiloculated mass that
is anechoic or contains scanty low-level echoes
VOL. 27, NO. 7, SEPTEMBER 1999
FIGURE 6. Neurilemoma. Transverse sonogram of the anterior thigh
shows a large neurilemoma with a capsule lying alongside the femur
(arrow).
and that shows distal acoustic enhancement.17–19
Nerve fibers may be splayed around the mass. In
my experience, approximately half the cases of
ganglia affecting the common peroneal nerve resolve spontaneously, without surgery. These may
be examples of compressive rather than invasive
neuropathies. Other sites where ganglia may
compress nerves include the elbow and the suprascapular notch.20,21 In addition to diagnosing ganglia, sonography may be used to guide aspiration
365
BEGGS
FIGURE 7. Neurilemoma. Longitudinal sonogram of the upper arm
shows cavitation (arrow) in a degenerated neurilemoma.
FIGURE 9. Intraneural ganglion. Longitudinal sonogram of the posterolateral aspect of the knee joint at the level of the fibular head
shows a well-defined ganglion within the common peroneal nerve.
The ganglion has a thin stalk and satellite lesions (arrows). Most ganglia are well defined.
mass (Figure 10).3,5,7 Friction at an amputation
site may result in a spindle neuroma of an intact
nerve.
MORTON’S NEUROMA
TRAUMATIC NEUROMA
Morton’s neuroma is a fibrotic swelling of the
plantar interdigital nerve, believed to be due to
overly tight shoes. Most patients are women.
Morton’s neuromas tend to become symptomatic
when they exceed 5 mm and may be multiple.
Ninety percent occur between the heads of the
second and third or third and fourth metatarsals.
Patients experience pain, paresthesia, and/or
swelling and often feel as if walking with a pebble
in the shoe.
On clinical examination, a Morton’s neuroma
may be palpable, and compression of the interdigital space or metatarsal heads may reproduce
Traumatic, stump, or amputation neuroma occurs
when a nerve is transected, whether or not the
limb is amputated. Attempted repair at the proximal end of the nerve continues for many months
after the original injury and results in a bulbous
swelling. Traumatic neuromas may cause pain,
but many are asymptomatic; therefore, in a patient with pain at a site of amputation, other
causes of the pain should be sought, eg, infection
or tumor recurrence. The demonstration of a typical mass in the line of the transected nerve is
diagnostic of traumatic neuroma. Sonography
shows a well-defined hypoechoic mass, and the
echogenic nerve may be visible running into the
FIGURE 10. Traumatic neuroma occurring after an above-knee amputation. Longitudinal sonogram of the posterior thigh just proximal to
the amputation site shows the echogenic nerve (arrow) running into
the neuroma.
FIGURE 8. Neurilemoma. Longitudinal color Doppler sonogram
(shown in gray-scale) of the flexor compartment of the forearm demonstrates increased vascularity at the periphery of a neurilemoma.
and decompression of ganglia to relieve nerve
compression.
366
JOURNAL OF CLINICAL ULTRASOUND
NERVE TUMORS
FIGURE 11. Morton’s neuroma. Plantar approach to sonographic examination. (A) Longitudinal sonogram shows the typical round/oval hypoechoic
mass. (B) Transverse sonogram shows the mass (arrows) between the second (2) and third (3) metatarsal heads. The irregular contour and plantar
extension seen here are uncommon.
symptoms. In these circumstances, the diagnosis
and site are obvious, and treatment (usually excision; less often steroid injection) should be instituted. Not infrequently, the diagnosis or the exact
interdigital space involved is uncertain. Sonography is then of value in demonstrating a solid, hypoechoic soft tissue mass between the metatarsal
heads,22–26 although disappointing results have
been reported.27 I use a plantar sonographic approach in cases of suspected Morton’s neuroma.
The patient and examiner sit diagonally across
from each other on either side of the examination
couch with the patient’s leg extended and the heel
resting on the examination couch. Palpation is
not usually required, but pressure on the dorsum
of the interdigital space occasionally brings a
small neuroma into view or makes it more conspicuous. Morton’s neuromas may be seen on longitudinal or transverse scans or both (Figure
11).22–26 The masses are usually oval or round but
may be irregular and spill out in a plantar direction. In a series from our institution,24 more than
90% of intermetatarsal masses demonstrated by
sonography were Morton’s neuromas; the remaining 10% were other benign lesions. Sonographic
demonstration of a solid mass also excludes the
possibility of a ganglion, which may present in a
similar way but does not require surgery. Recurrence of neuromas after excision is unusual, and
the recurrent neuromas appear identical to primary neuromas.
VOL. 27, NO. 7, SEPTEMBER 1999
CONCLUSION
Sonography is of value in the assessment of nerve
tumors. Characteristic clinical features, anatomic
sites, and sonographic appearances are diagnostic
in many cases.
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