AJR 2000; 175:1711-1719
© American Roentgen Ray Society
An Illustrated Tutorial of Musculoskeletal Sonography
Part 4, Musculoskeletal Masses, Sonographically Guided Interventions, and Miscellaneous Topics
John Lin1,
Jon A. Jacobson,
David P. Fessell,
William J. Weadock and
Curtis W. Hayes
1
All authors: Department of Radiology, The University of Michigan Medical
Center, 1500 E. Medical Center Dr., TC 2910, Ann Arbor, MI 48109-0326.
Received December 8, 1999;
accepted after revision February 10, 2000.
Address correspondence to J. Lin.
Introduction
Musculoskeletal sonography can be a reliable, expedient, and readily
accessible alternative to other, more costly, imaging techniques such as MR
imaging. Sonography is adaptable to many situations and is not restricted by
regimented standardized protocols. The sonographer interacts directly with the
patient, allowing flexibility in performing the examination and often
resulting in greater diagnostic effectiveness. This is particularly useful for
evaluating musculoskeletal masses and infection, or for performing
sonographically guided interventions.
Musculoskeletal Masses
Sonography can be useful for the assessment of musculoskeletal soft-tissue
masses. High frequency probes (9-13 MHz) are indicated for evaluation of
superficial structures or subcutaneous masses, and deeper lesions require a
lower frequency transducer (3.5-7 MHz).
Because of its small field of view, traditional sonography is limited in
its capability to directly image lesions involving large anatomic segments.
The split-screen feature available on most units allows better visualization
of larger lesions by doubling the field of view
(Fig. 1). This feature is also
useful for side-to-side contralateral comparisons. The extended field-of-view
imaging feature recently introduced (SieScape; Siemens Medical Systems,
Iselin, NJ) allows the operator to obtain panoramic images over a large area
by continuously scanning the area of interest
[1,
2]
(Fig. 2).
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Fig. 1. —18-year-old man with right foot drop. Longitudinal
split-screen sonogram of posterolateral aspect of right leg just distal to
knee reveals long superficial fusiform lesion (arrows) in
distribution of common peroneal nerve consistent with peripheral nerve sheath
tumor. Surgical excision and histopathologic examination confirmed
neurofibroma.
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Fig. 2. —35-year-old man with large hematoma. Longitudinal extended
field-of-view sonogram of posterior thigh shows large complex relatively
hypoechoic lesion (arrows) in hamstring muscle compartment consistent
with large hematoma. Extended field-of-view function allows complete coverage
of this large lesion. p = proximal, d = distal.
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Both static and dynamic evaluations can be useful during sonographic
examination in the assessment of soft-tissue lesions. Standard characteristics
such as size, shape, location, and echogenicity can be determined with static
evaluation. The dynamic evaluation may incorporate different maneuvers to help
define the relationship of the lesion to adjacent structures and to reproduce
symptoms in certain situations. For example, having the patient stand may
increase blood flow in a vascular lesion in the lower extremities, and muscle
contraction can accentuate appreciation of a lesion such as muscle
herniation.
The fact that sonography can determine if a mass is cystic or solid is well
established. Simple cystic lesions can be considered benign. Imaging
characteristics of solid masses and complex cystic lesions are generally
nonspecific. Color and power Doppler sonography allow assessment of tumor
vascularity. Further imaging or tissue biopsy is usually indicated for
diagnosis. However, certain features can be helpful to formulate an
appropriate differential diagnosis.
Specific Musculoskeletal Masses
Lipomas frequently involve the superficial soft tissues and can be
evaluated on sonography. The elongated dimensions of the lesion usually
parallel the skin surface with well-defined to ill-defined margins. Lipomas
are typically homogeneous in echotexture and are most commonly slightly
hyperechoic to the adjacent subcutaneous fat (although this is variable and
some lipomas show iso- or hypoechogenicity)
[3] (Figs.
3A,3B
and 4).
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Fig. 3A. —49-year-old woman with superficial lipoma. Longitudinal
(A) and transverse (B) sonograms of medial aspect of upper arm
show disk-shaped lesion (arrows) in subcutaneous tissues just
superficial to biceps muscle. This lesion has well-defined echogenic margins
and is minimally hyperechoic to adjacent muscle. Findings were consistent with
superficial lipoma.
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Fig. 3B. —49-year-old woman with superficial lipoma. Longitudinal
(A) and transverse (B) sonograms of medial aspect of upper arm
show disk-shaped lesion (arrows) in subcutaneous tissues just
superficial to biceps muscle. This lesion has well-defined echogenic margins
and is minimally hyperechoic to adjacent muscle. Findings were consistent with
superficial lipoma.
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Fig. 4. —69-year-old woman with superficial lipoma. Longitudinal
sonogram of medial plantar aspect of right foot shows noncompressible slightly
lobulated hypoechoic lesion (arrows) in subcutaneous tissues. C =
medial cuneiform, M = first metatarsal.
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Hemangiomas have a variable heterogeneous echogenicity, corresponding to
the different elements that constitute the lesion
[4]. Increased flow can be seen
filling vascular channels with power Doppler sonography, and hyperechogenic
foci with distal shadowing representing phleboliths may be present (Fig.
5A,5B,5C,5D,5E).
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Fig. 5A. —43-year-old man with hemangioma. Transverse sonogram of mid
forearm shows relatively hypoechoic lesion (solid arrows) and
echogenic central foci (arrowhead) with associated shadowing adjacent
to radius (open arrows).
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Fig. 5C. —43-year-old man with hemangioma. Anteroposterior radiograph
of forearm shows findings consistent with hemangioma: rounded calcification
representing phlebolith (arrow) and cortical scalloping with mild
periosteal bone proliferation.
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Fig. 5D. —43-year-old man with hemangioma. Axial proton
density—weighted (D) and T2-weighted (E) MR images show
hyperintense striated—septated mass (arrows) with serpiginous
vascular channels characteristic of hemangioma.
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Fig. 5E. —43-year-old man with hemangioma. Axial proton
density—weighted (D) and T2-weighted (E) MR images show
hyperintense striated—septated mass (arrows) with serpiginous
vascular channels characteristic of hemangioma.
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Peripheral nerve sheath tumors may have a characteristic appearance on
sonography consistent with the anatomic morphology of the tumors. A
well-defined hypoechoic fusiform mass located in the appropriate nerve
distribution suggests a peripheral nerve sheath tumor
[5]
(Fig. 6). The additional
finding of distal acoustic enhancement in some cases may be helpful to suggest
the diagnosis of peripheral nerve sheath tumor. This lesion can be
specifically diagnosed when the entering and exiting nerves are identified.
Like with MR imaging, differentiating between a malignant and benign
peripheral nerve sheath tumor is difficult with sonography.
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Fig. 6. —21-year-old man with neurofibromatosis. Longitudinal sonogram
of proximal forearm volarly shows fusiform hypoechoic lesion (arrows)
distributed in median nerve. Median nerve can be seen to "enter"
and "exit" lesion (arrowheads), which is diagnostic for
peripheral nerve sheath tumor.
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The sonographic appearance of pigmented villonodular synovitis is
nonspecific, similar to other causes of synovitis such as rheumatoid
arthritis. Characteristic findings include markedly thickened synovium, joint
effusion (which may be loculated), and heterogeneous echogenic masses that
typically show hyperemia (Fig.
7A,7B).
Osseous erosions may also be identified when present
[6].
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Fig. 7A. —43-year-old woman with pigmented villonodular synovitis.
Longitudinal sonogram of popliteal fossa shows nodular lobulated lesion
(black arrows), which is relatively hypoechoic near posterior tibia
plateau (white arrows). Note posterior femoral cortex
(arrowheads).
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Fig. 7B. —43-year-old woman with pigmented villonodular synovitis.
Longitudinal power Doppler sonogram, obtained in same location as A,
reveals increased flow. This finding was surgically proven pigmented
villonodular synovitis.
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Sonography has a limited role in the evaluation of osseous lesions, which
should generally be investigated initially on radiography, followed by CT, MR
imaging, or both. Sonography has been used to measure the thickness of the
cartilaginous cap of osteochondromas
[7] (Fig.
8A,8B).
A glomus tumor can be detected on sonography as a small rounded lesion located
beneath the nail of a digit [8]
(Fig.
9A,9B).
Increased flow on power Doppler sonography may be useful to help identify
these lesions, which can be difficult to recognize on gray-scale imaging.
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Fig. 8A. —22-year-old man with osteochondroma. Longitudinal sonogram of
medial thigh proximal to knee in region of palpable mass shows exophytic bone
lesion (arrowheads) seen in continuity with distal medial femur
(Fem). No evidence for abnormal thickening of cartilage cap (arrows)
was seen.
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Fig. 8B. —22-year-old man with osteochondroma. Anteroposterior
radiograph of distal femur shows osseous excrescence (arrowheads)
extending from medial metadiaphysis consistent with osteochondroma.
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Fig. 9A. —37-year-old woman with glomus tumor of left thumb.
Longitudinal split-screen sonogram shows relatively hyperechoic lesion
(arrowheads) present under nail of thumb (left side) compared with
normal appearance of contralateral thumb (right side).
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Fig. 9B. —37-year-old woman with glomus tumor of left thumb. Coronal
fast spin-echo proton density—weighted fat-saturated MR image shows
markedly hyperintense lesion (arrow) involving terminal tuft region
of left thumb. Findings represented glomus tumor.
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Sonography has been shown to be effective for the assessment of recurrent
soft-tissue sarcoma [9]
(Fig. 10). Sonography is not
widely used for this purpose because it is operator-dependent, and
longitudinal follow-up studies are not easily compared with prior
examinations.
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Fig. 10. —35-year-old woman with recurrent radiation-induced malignant
fibrous histiocytoma to soft tissues just anterior to sternum. Transverse
sonogram of anterior sternum shows multilobulated hypoechoic soft-tissue
masses (black arrows) anterior to sternum (white arrows).
Biopsy revealed recurrent malignant fibrous histiocytoma. a = anterior.
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Miscellaneous Topics
Foreign bodies invisible on conventional radiographs can often be easily
identified, usually appearing hyperechoic, on sonograms
[10]. Additionally, the
involvement of adjacent soft-tissue structures, the inflammatory response, and
possible abscess formation can all be depicted on sonography (Figs.
11 and
12).
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Fig. 11. —36-year-old man with foreign bodies (cactus thorns) in left
ring finger. Transverse sonogram of dorsal aspect of fourth digit proximal
interphalangeal joint shows presence of two foreign bodies within soft tissues
consisting of parallel hyperechoic lines (arrows). Tubular hypoechoic
space between parallel hyperechoic lines represents hollow center of cactus
thorn. Note cortex of adjacent phalynx (arrowheads).
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Fig. 12. —57-year-old man with foreign body (suture material) in thumb.
Longitudinal sonogram of volar aspect of thumb shows echogenic linear foreign
body (arrows) present within substance of flexor pollicis longus
tendon (arrowheads). He had undergone surgical repair of this tendon
20 years before sonographic examination.
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Sonographically, cellulitis appears as diffuse thickening of involved
subcutaneous and soft tissues with reticulated disorganized anechoic stranding
as a result of distended lymphatic channels within the tissue spaces
[11]
(Fig. 13A). Power Doppler
sonography may show a variable degree of increased flow due to inflammation
(Fig. 13B).
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Fig. 13A. —42-year-old woman with cellulitis. Longitudinal sonogram of
dorsal aspect of foot shows anechoic reticulation (double arrows)
present throughout thickened subcutaneous tissues representing dilated
lymphatic channels.
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Fig. 13B. —42-year-old woman with cellulitis. Longitudinal power Doppler
sonogram of dorsal soft tissues of foot reveals increased flow consistent with
inflammation. Patient had infectious cellulitis related to diabetes
mellitus.
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The sonographic appearance of abscesses in the soft tissues is quite
variable, from the appearance of a simple anechoic fluid collection to a
complex heterogeneous lesion with internal debris and septations. Increased
flow with power Doppler imaging is usually present, frequently in a peripheral
rimlike pattern [11,
12]
(Fig. 14). Subperiosteal
lesions can be evaluated sonographically, particularly in pediatric patients,
to determine the extent of involvement, and direct aspiration can be used to
assess possible infection (Fig.
15A,15B).
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Fig. 14. —22-year-old man with abscess. Transverse power Doppler
sonogram of anterior thigh shows hypoechoic lesion (A) with peripheral pattern
of increased flow (arrows) suggestive of abscess. Sonographically
guided aspiration of lesion revealed infection.
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Fig. 15A. —11-year-old boy with subperiosteal abscess of distal fibula.
Longitudinal sonogram of distal fibula shows heterogeneous slightly
hyperechoic subperiosteal collection (black arrows), which extends
distally to growth plate (white arrow) where periosteum is tightly
attached. Note thin echogenic elevated periosteum (open arrows) and
echogenic cortex (arrowheads).
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Hematomas can be similar in appearance to complex abscesses. However, the
clinical scenario usually helps differentiate between these lesions (Figs.
2 and
16A,16B).
Sonographically guided aspiration can be performed to alleviate pressure from
a large hematoma and to exclude infection. Serial sonography can be used for
follow-up of large or worrisome hematomas and to confirm healing and
resolution of the lesion.
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Fig. 16A. —15-year-old boy with large infected hematoma. Longitudinal
sonogram of proximal left upper extremity from anterolateral approach shows
complex heterogeneous cystic lesion (arrows) in region of previous
major trauma representing hematoma.
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Fig. 16B. —15-year-old boy with large infected hematoma. Axial CT scan
of proximal left upper extremity shows multiple large areas of fluid and
soft-tissue attenuation (arrows) representing hematomas. Aspiration
revealed infected hematomas. Also note deformity of medial humerus with
fragments from comminuted fractures (arrowhead).
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Sonographically Guided Interventions
Sonography is a useful technique for guidance of percutaneous needle biopsy
or aspiration [13,
14]. It provides multiplanar
imaging of the target and adjacent structures including vessels and nerves,
with continuous real-time visualization of the needle. With sonography,
patient positioning is not limited by the constraints of the machine like
CT-guided procedures sometimes are (Fig.
17A,17B,17C).
Other advantages include the portability of sonography and the absence of
ionizing radiation. In soft-tissue masses with necrosis or hemorrhage, power
Doppler sonography can help determine the viable portion of a lesion,
resulting in a higher yield for diagnostic biopsies. Immediate or delayed
scanning after the procedure can be performed to evaluate for residual fluid
after aspiration or biopsy complications.
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Fig. 17A. —70-year-old man with hemangiopericytoma. Axial fast spin-echo
proton density—weighted fat-saturated MR image shows
high-signal-intensity soft-tissue mass (arrows) in adductor
compartment of right proximal thigh.
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Fig. 17B. —70-year-old man with hemangiopericytoma. Transverse sonogram
of medial thigh, with leg held in abducted and externally rotated position,
shows fairly well-defined relatively hypoechoic mass (arrows). m =
medial, p = proximal, d = distal.
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Fig. 17C. —70-year-old man with hemangiopericytoma. Transverse sonogram
obtained during sonographically guided percutaneous core biopsy shows deployed
needle (arrowheads) extending through mass (arrows).
Sonography was used for biopsy guidance in part because of anatomic location
of lesion and surgeon's request for a medial compartment approach, which would
be difficult with CT. Histopathologic examination revealed
hemangiopericytoma.
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Closing Remarks
As we conclude our four-part pictorial essay series
[15,16,17],
it is our hope that the reader will have a greater appreciation and awareness
of the current clinical applications of musculoskeletal sonography. There are
many advantages of sonography over other imaging modalities; the few
disadvantages can generally be overcome with proper training and equipment. As
technical innovations continue to evolve, the potential role for
musculoskeletal sonography will continue to expand.
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Top
Introduction
Musculoskeletal Masses
