Introduction
Soft tissue tumors originate from nonepithelial extraskeletal tissues, such as fat,
muscle, tendons, peripheral nerves, blood vessels, and fibrous tissue.[1 ] More than 15% of soft tissue tumors occur in the hand, and, among these, ∼ 95% are
benign.[2 ] This review discusses soft tissue masses of the hand in accordance with the revised
2020 World Health Organization (WHO) Classification of Soft Tissue Tumors, as well
as other soft tissue masses of varying origin that may be encountered in both routine
and unusual clinical practice. The 2020 WHO classification ([Table 1 ]) organizes soft tissue tumors into 11 categories and further stratifies them by
biological behavior into benign, intermediate (locally aggressive), and malignant
entities.[3 ]
Table 1
Characteristics of six solid soft tissue types cited in the text[a ]
Category
Benign
Locally aggressive
Malignant
Adipocytic
Lipoma
Atypical lipomatous tumor
Liposarcoma
Fibroblastic and myofibroblastic
Palmar fibromatosis
Epithelioid sarcoma
Solitary fibrous tumor, malignant
Fibrohistiocytic tumors
Tenosynovial giant cell tumor
Pericytic tumors
Glomus tumor
Peripheral nerve sheath tumors
Schwannoma
Neurofibroma
Malignant peripheral nerve sheath tumor
Tumors of uncertain differentiation
Synovial sarcoma
a According to the 2020 World Health Organization Classification of Soft Tissue Tumors.
Imaging Recommendations According to the 2023 Guidelines of the European Society of
Musculoskeletal Radiology
For the primary diagnosis of local soft tissue tumors, the radiologist should carefully
consider the patient's medical history. Relevant aspects include the time of initial
detection, any recent changes in size, and a history of trauma or previous surgery
in the affected region. However, it is crucial that diagnostic evaluation not be delayed
based solely on the patient's subjective attribution of the lesion to a traumatic
event because it may lead to misinterpretation or underestimation of a potentially
serious pathology.[4 ]
Ultrasound
According to the 2023 European Society of Musculoskeletal Radiology (ESSR) guidelines,
US is the appropriate first-line imaging modality for suspected soft tissue tumors
that are < 5 cm and located superficially.[4 ] A high-frequency linear transducer (10–20 MHz) is recommended for optimal evaluation
of these lesions.[5 ] If the lesion is superficial and demonstrates typical sonographic features, US can
often provide a reliable diagnosis without the need for further imaging.[6 ] Doppler US plays a crucial role in characterizing soft tissue masses. In particular,
vascular malformations may demonstrate slow filling during dynamic assessment with
compression and release maneuvers.[5 ]
Benign lesions with characteristic US features, such as anechoic, avascular well-circumscribed
cystic structures, can be confidently diagnosed as simple cysts or synovial/ganglion
cysts. Other benign entities, such as superficial lipomas, superficial fibromatosis,
and foreign body granulomas (when clinical history supports the diagnosis), may also
be accurately assessed with US.[4 ] In cases where US findings are inconclusive, or if the lesion demonstrates atypical
features, MRI and/or biopsy should be pursued to establish a definitive diagnosis.
In addition, small superficial lesions that appear benign but show interval growth
warrant biopsy. For lesions measuring < 2 to 3 cm, an excisional biopsy may be considered
appropriate.[4 ]
[7 ]
Magnetic Resonance Imaging
In cases of clinical suspicion of malignancy, history of rapid growth, primary osseous
or joint involvement, and lesion size > 5 cm, MRI should be chosen over US as the
imaging modality. Furthermore, MRI should be performed before biopsy.[4 ] The recommended field strength for evaluating soft tissue tumors is at least 1.5
T.
The basic imaging protocol should include T1-weighted and fluid-sensitive fat-saturated
sequences, both oriented parallel to the long axis of the tumor. Axial sequences with
high spatial resolution are necessary to delineate the lesion's margins accurately
and assess involvement of adjacent compartments, neurovascular structures, bone, and
joints.[4 ]
Following intravenous gadolinium administration, dynamic contrast-enhanced sequences
may help differentiate benign from malignant soft tissue tumors. Subtraction techniques
are particularly useful in lesions with intrinsically high signal intensity on T1-weighted
images, such as melanin or methemoglobin-containing entities.[4 ] A cutaneous marker should be applied before the examination to aid in localization.[4 ]
Projection Radiographs
Radiographs help identify intralesional mineralization patterns and assess potential
bone involvement associated with soft tissue masses. Radiographs should be obtained
in at least two orthogonal views.[4 ]
Soft Tissue Masses: An Overview
Adipocytic Tumors
Lipoma
Pathology
Lipomas are benign adipocytic tumors composed of mature adipose tissue, originating
from mesenchymal preadipocytes.[5 ]
[8 ] They typically present as soft painless masses and can occur in either subcutaneous
or deeper locations. Importantly, they do not infiltrate the surrounding tissue.[5 ]
[9 ] Although lipomas are the most common soft tissue tumors, they are relatively rare
in the hand, accounting for only 1 to 3.8% of soft tissue tumors in that region. In
the fingers, lipomas are extremely rare, with an incidence of ∼ 1%.[5 ]
[8 ]
[10 ] In the hand, lipomas most commonly occur intramuscularly at the thenar and hypothenar
eminences, where they may cause paresthesia due to compression of adjacent nerve branches.
Other common locations include the carpal tunnel and Guyon's canal.[11 ] The recommended treatment is excisional biopsy or marginal excision, particularly
in cases where the lesion is close to a nerve. Recurrence rates are > 5% in such cases.[7 ]
[9 ]
[11 ]
Imaging
On US, lipomas present as well-defined typically homogeneous and hyperechoic lesions,
although they may also appear hypo- or isoechoic.[5 ] On MRI, they demonstrate homogeneous high signal on T1-weighted sequences and low
signal intensity on T2-weighted fat-saturated sequences. They characteristically have
low apparent diffusion coefficient values and demonstrate no or only minimal contrast
enhancement.[5 ]
Atypical Lipomatous Tumors and Liposarcomas
Pathology
Liposarcomas make up 20% of all mesenchymal malignant tumors and are classified into
five subtypes[12 ]: well-differentiated liposarcoma (WDLS), dedifferentiated, myxoid, pleomorphic,
and myxoid pleomorphic liposarcoma.[1 ] Depending on their anatomical location, WDLS are referred to as atypical lipomatous
tumors (ALTs) when arising in the extremities, chest wall, or abdominal wall.[13 ] The ALTs most frequently occur in the extremities, particularly the lower limbs,
with only a few cases reported in the hand.[14 ]
[15 ]
Imaging
On MRI, a tumor length > 10 cm and the presence of thick septa or nonfatty areas are
associated with ALT. The nonfatty nodules correspond to regressive changes with fat
necrosis, calcification, fibrosis, inflammation, and myxoid changes. Dedifferentiated
nodules arising in ALT of the hand are extremely rare.[13 ]
Lipofibromatous Hamartoma
Pathology
A lipofibromatous hamartoma (LFH) is a rare benign neoplasm composed of fibroadipose
tissue that affects peripheral nerves, most frequently in the upper extremity. Among
the nerves of the upper limb, the median nerve is most commonly involved, although
the radial nerve, ulnar nerve, digital nerves, and brachial plexus may also be affected.[16 ] The lesion is believed to be congenital and tends to grow very slowly. Typically,
a long-standing history of a painless mass dates back to childhood, with patients
often becoming symptomatic in the third or fourth decade of life.[17 ] When the median nerve is affected, patients frequently present with symptoms of
carpal tunnel syndrome.[16 ] Clinically, LFH is often associated with macrodactyly that occurs in ∼ 30% of cases.[18 ]
Imaging
On US ([Fig. 1A ]), LFH has a characteristic appearance. The affected nerve appears enlarged with
multiple hypoechoic coaxial “cables” surrounded by a hyperechoic rim. On MRI ([Fig. 1B ]), the imaging modality of choice for surgical planning, an enlarged nerve containing
15 to 16 coaxial cable-like structures is revealed. These represent 2- to 3-mm axonal
bundles encased in epineural fibrous tissue and surrounded by fat. In most cases,
the imaging findings are so typical that biopsy is not required.[16 ]
Fibroblastic and Myofibroblastic Lesions
Palmar Fibromatosis
Pathology
Palmar fibromatosis, also known as Dupuytren's disease or Dupuytren's contracture,
is a common condition. It is a benign fibroproliferative disorder characterized by
the formation of subcutaneous fibrous nodules with involvement of the palmar aponeurosis
and variably the subcutis and dermis. In progressive stages of the disease, cordlike
attachments may develop along the flexor tendons, ultimately resulting in flexion
contractures of the fingers.[19 ] According to a 2020 meta-analysis, the worldwide prevalence is 8.2%.[20 ] It affects ∼ 20% of individuals > 65 years of age and is associated with other fibromatoses,
as well as systemic conditions such as diabetes mellitus, alcohol abuse, and epilepsy.[19 ] The disease is classically divided into three stages: proliferative, involutional,
and residual.[20 ] These lesions are typically situated immediately superficial to the flexor tendons,
most frequently in the region of the distal metacarpal bones.
Imaging
The US features ([Fig. 2A ]) vary depending on the disease stage. In the proliferative phase, the nodules, typically
located over the metacarpophalangeal and proximal interphalangeal joints, appear hypoechoic
relative to the flexor tendons. During the involutional and residual phases, as collagen
production increases and the nodules contract, they become iso- to hyperechoic compared
with the surrounding tendons.[20 ]
Fig. 2 Palmar fibromatosis. A 52-year-old patient presents with thickening and nodular skin
changes on the palmar aspect of the hand, 2 years after carpal tunnel release surgery.
(A ) On ultrasound, a hypoechoic structure is identified superficial to the flexor tendon,
in contact with the palmar aponeurosis. In the accompanying illustration, the red
structure represents the flexor tendon; the blue structure indicates the fibromatous
nodule. (B ) Magnetic resonance imaging of the hand demonstrates a T2-hypointense subcutaneous
nodule. The arrow indicates the palmar aponeurosis.
On MRI ([Fig. 2B ]), palmar fibromatosis appears as focal nodules or cordlike structures arising from
the palmar aponeurosis. These lesions are generally of low signal on T1-weighted images.
Lesions with high cellularity may show relatively increased signal intensity on T2-weighted
images, whereas lesions with a predominantly collagenous matrix tend to remain low
in signal on T2-weighted sequences.[5 ]
[21 ] They usually exhibit no internal vascularization. In a study by Morris et al, only
3 of 54 lesions demonstrated hypervascularity. Calcifications may also be present
within the nodules.[19 ]
Epithelioid Sarcoma
Pathology
Epithelioid sarcoma is a rare type of sarcoma, accounting for ∼ 1% of all adult soft
tissue sarcomas. It is a slow-developing malignant tumor that typically occurs in
the distal extremities. Histopathologically, epithelioid sarcoma may be mistaken for
benign conditions such as Dupuytren's disease. The peak incidence is reported at ∼
35 years of age. The two morphological variants are (1) a proximal type that presents
as deep infiltrating soft tissue masses in the midline of the trunk, proximal limbs,
or limb girdles, and (2) a classic or distal type. The distal type presents as superficial
slow growing painless nodules that may lead to chronic nonhealing ulcers. In up to
27% of cases, it is associated with previous trauma or scar tissue. Initial treatment
involves wide local excision or amputation, with or without adjuvant radiotherapy.[22 ]
Imaging
On MRI ([Fig. 3 ]), the classic type typically appears as a mass with heterogeneous signal intensity,
often infiltrating along fascial planes and neurovascular bundles. Imaging is essential
to assess the extent of the entity accurately.[22 ]
Fig. 3 Epithelioid sarcoma. A 21-year-old woman presents with a subcutaneous lesion on the
palmar surface of the right hand that she had first noticed 2 years earlier; however,
biopsy was delayed. Over the past 2 years it has shown slow growth. Biopsy revealed
epithelioid sarcoma. (A ) Axial T2-weighted image depicts the lesion (arrow) when it was first noticed. (B–D)
Magnetic resonance imaging of the lesion at the time of biopsy. (B ) The lesion is hyperintense on proton-density-weighted Spectral Adiabatic Inversion
Recovery (SPAIR), (C ) hypointense on T1–weighted sequence (red circle), and (D ) shows marked contrast enhancement (red arrow). The mass is infiltrating all the
thenar muscles as well as the cutis and subcutis. In addition, denervation edema of
the thenar musculature is observed, raising suspicion for involvement of the motor
thenar branch of the median nerve.
Solitary Fibrous Tumor, Malignant
Pathology
A solitary fibrous tumor (SFT) is a rare fibroblastic mesenchymal tumor that can arise
in any anatomical location, with an estimated incidence of only one new case per million
people per year.[23 ]
[24 ] According to the fifth edition of the WHO Classification of Soft Tissue and Bone
Tumors, extracranial SFTs are categorized as benign SFT (intermediate category, locally
aggressive), SFT not otherwise specified (intermediate category, rarely metastasizing),
and malignant SFT. Local recurrence or distant metastasis occurs in ∼ 10 to 40% of
patients with SFT.[24 ] Due to the variable clinical behavior of SFTs, it remains challenging to determine
which tumor- and patient-specific factors predict aggressive progression. As a result,
several risk stratification models have been developed to estimate the individual
risk of recurrence or metastasis.[24 ]
[25 ]
Imaging
On MRI ([Fig. 4 ]), SFTs typically appear homogeneously isointense to muscle on T1-weighted images
and show variable signal intensity on T2-weighted sequences. A low T2 signal indicates
higher cellularity and less fibrosis, whereas myxoid changes result in markedly high
T2 signal intensity. Following intravenous gadolinium administration, SFTs usually
demonstrate strong contrast enhancement.[26 ]
Fig. 4 Malignant solitary fibrous tumor. A 34-year-old patient presents with a progressively
enlarging lesion surrounding the metacarpal thumb area. There is no restricted range
of motion. (A ) The lesion is inhomogeneously hyperintense on a coronal proton-density-weighted
image and (B ) nearly isointense to muscle on a axial T1-weighted image. (C ) The postcontrast T1-weighted sequence demonstrates an inhomogeneously marked enhancement.
Fibrohistiocytic Tumors
Tenosynovial Giant Cell Tumor
Pathology
A tenosynovial giant cell tumor (TSGCT) is the second most common benign tumor of
the hand, typically affecting patients from 30 to 50 years of age, predominantly female.[27 ]
[28 ] Various theories exist regarding its pathophysiology, including neoplastic, inflammatory,
trauma related, immune mediated, or association with abnormal lipid metabolism. The
most widely accepted theory describes it as a reactive or regenerative hyperplasia
accompanied by an inflammatory process. Recent literature has identified a chromosomal
translocation involving chromosome 1p13 in most tumors.[27 ]
[29 ]
In the hand, TSGCT most commonly presents in its localized form as focal masses associated
with tendons. A single nodule typically is present, although multiple nodules may
occur. Clinically, they appear as firm, painless swellings over the flexor aspect
of the hand.[3 ]
[27 ]
[29 ] A TSGCT is classified into nodular and diffuse types according to Al-Quattan's classification.[29 ] Diffuse-type TSGCT often infiltrates nearby soft tissues and joints, making surgical
removal more complicated. Treatment consists of marginal excision with clear margins.
Although the lesion is benign, the incidence of local recurrence is high, with rates
of up to 44%.[27 ]
[30 ] Risk factors for local recurrence are adjacent degenerative joint disease, localization
at the distal interphalangeal joint or the interphalangeal joint of the thumb, increased
cellularity and mitotic activity, and tumor subtype.[27 ]
[29 ] In incidences of diffuse-type TSGCT, regular MRI follow-up is necessary to monitor
recurrence.[30 ]
Imaging
On radiographs, TSGCT exhibits soft tissue density or may cause bony erosions.[29 ] On US, TSGCT presents as hypoechoic masses adjacent to the tendon sheath and shows
internal vascularization. On dynamic US, they do not move with the underlying tendon.[28 ] On MRI, the lesions demonstrate low signal intensity on both T1- and T2-weighted
images due to the presence of hemosiderin. Importantly, blooming artifacts are common
on gradient-echo sequences as a result of hemosiderin deposition. Following intravenous
contrast administration, enhancement is typically observed.[28 ]
[31 ]
Pericytic Tumors
Glomus Tumor
Pathology
Glomus tumors are benign vascular neoplasms that arise from the glomus body, a neuro-myovascular
structure involved in thermoregulation. They account for ∼ 1 to 5% of soft tissue
tumors of the hand.[32 ] About 75% of glomus tumors occur in the hand, and nearly all of these are located
in the subungual region.[33 ] Glomus tumors are more common in women between 30 and 50 years of age and usually
not associated with other conditions.[34 ] Clinical features include blue discoloration of the nail, nail deformity, and a
palpable nodule.[34 ]
Solitary glomus tumors, which are more frequent, present with the classic triad of
localized tenderness, severe pain, and sensitivity to cold.[32 ] An association between glomus tumors and neurofibromatosis type 1 (NF1) was also
reported.[35 ] Treatment consists of complete surgical excision. Reported recurrence rates in the
literature range from 4% to 50%, and a distinction is made between early recurrence,
often attributed to incomplete excision, and late recurrence that may represent a
new lesion developing adjacent to the original excision site.[32 ]
Imaging
On US, glomus tumors appear as hypoechoic solid masses with increased through transmission
and small cystic components, showing marked blood flow on both power and color Doppler
imaging. On MRI, they demonstrate high signal intensity on T2-weighted images, intermediate
signal on T1-weighted images, and enhancement following intravenous gadolinium administration.
Small glomus tumors (< 1 cm) typically show homogeneous enhancement. Magnetic resonance
imaging is particularly useful in identifying tumor recurrence.[33 ]
Peripheral Nerve Sheath Tumors
Peripheral nerve sheath tumors (PNSTs) of the hand account for < 5% of all tumors
arising from the hand. The overwhelming majority of these tumors are benign, and the
incidence of malignant peripheral nerve sheath tumors (MPNSTs) is extremely low. Benign
PNSTs of the hand consist mainly of schwannomas, neurofibromas, and perineuriomas.[36 ] Most of the lesions occur sporadically and are not associated with NF.[10 ] A PNST usually presents in adulthood between 20 and 30 years of age.[5 ] The typical clinical presentation is a slow-growing soft tissue mass, with pain
and sensory loss or weakness in the hand. In case of large size (> 5 cm), rapid size
progression, or an increase in pain, MPNST must be considered. A positive Hoffmann-Tinel
sign of the tumor is common. Therapy of these tumors depends on the symptoms, such
as pain or neurologic deficits.[5 ]
[36 ]
Schwannoma (Neurinoma)
Pathology
Schwannomas arise from Schwann cells that surround peripheral nerves and tend to originate
from deeper and larger nerves, particularly the ulnar nerve.[5 ] They are the most common benign PNSTs, accounting for ∼ 5% of all soft tissue tumors,
and can occur throughout the body. Between 3% and 19% of schwannomas develop in the
upper extremities.[36 ]
[37 ] These tumors can occur at any age and have no sex predilection.[36 ] Although most cases are sporadic, schwannomas may also be associated with genetic
conditions such as NF2 and, less commonly, NF1.[37 ] Clinically, schwannomas typically present as a slow-growing mass, often accompanied
by paresthesia in the distribution of the affected nerve.[38 ]
Imaging
On US, neurogenic tumors generally appear as fusiform masses with a “dural tail sign,”
representing the entering and exiting nerve fascicles. Schwannomas are usually eccentric
relative to the parent nerve, helping differentiate them from neurofibromas. In case
of internal cystic changes, necrosis, or hemorrhage, they show a heterogeneous echogenicity.[5 ]
On MRI, schwannomas typically appear iso- to hypointense on T1-weighted images and
hyperintense on T2-weighted sequences, with postcontrast enhancement. Heterogeneous
signal intensity and enhancement suggest internal hemorrhage or myxoid/cystic degeneration.
Additional imaging signs, not specific to schwannomas but may be present in other
neurogenic tumors, include the “target sign” (a central low to intermediate T2 signal
indicating fibrous tissue and a peripheral high T2 signal indicating myxoid tissue).[37 ] The MRI features more suggestive of schwannoma are the “bright rim sign” (peripheral
high T2 signal), the absence of significant peritumoral edema, and a non-lobulated
shape.[37 ]
Neurofibroma
Pathology
Neurofibromas are relatively common benign PNSTs. Differentiation between schwannomas
and neurofibromas is clinically important because neurofibromas contain intratumoral
nerve fibers. Neurofibromas are classified into four subtypes based on anatomical
location and gross appearance: plexiform neurofibromas; intraneural neurofibromas;
massive soft tissue neurofibromas; and localized cutaneous neurofibromas, with this
last one the most common type.[36 ] Plexiform neurofibromas are considered pathognomonic for NF1 ([Fig. 5A ]) and carry an increased risk of malignant transformation.[39 ]
Fig. 5 Neurofibroma. A 58-year-old patient with known neurofibromatosis type 1 and numerous
cutaneous neurofibromas presented with a rapidly enlarging, painful mass on the palm.
Due to the clinical signs of rapid growth, pain, and ulceration, features that are
concerning for malignant peripheral nerve sheath tumor, surgical excision was performed.
Histopathologic analysis confirmed a benign neurofibroma with no evidence of malignant
transformation. (A ) Palmar view of the hand showing multiple nodules and a surface ulceration. (B ) Ultrasound revealed an inhomogeneously hypoechoic lesion with cystic components
and internal vascularization. (C ) Fluorodeoxyglucose positron emission tomography/computed tomography demonstrates
a maximum standardized uptake value of 5.5 g/mL, indicated by the red arrow. The black
arrows indicate the numerous cutaneous neurofibromas.
Neurofibromas typically occur in a younger population, most often in the third to
fourth decade of life, and show no sex predilection.[36 ] Most neurofibromas occur sporadically, with only ∼ 10% associated with NF1.[40 ] In the hand, neurofibromas often arise near flexion creases and cutaneous nerves.[41 ] Clinically, they present as nodules that may cause varying degrees of pain or peripheral
nerve dysfunction.[41 ]
Imaging
On US ([Fig. 5B ]), plexiform neurofibromas appear as predominantly hypoechoic, well-confined masses
arising from multiple nerve fascicles. Neurofibromas are characteristically concentric
relative to the nerve, in contrast to schwannomas that tend to be eccentric. In addition,
neurofibromas typically involve multiple fascicles, unlike schwannomas that are more
often limited to a single fascicle.[36 ]
[39 ]
On MRI, the “target sign,” a central low T2 signal and peripheral high T2 signal,
can be seen in neurofibromas, as well as other neurogenic tumors, although it is observed
less frequently in neurofibromas compared with schwannomas on MRI.[41 ] Fluorodeoxyglucose positron emission tomography/computed tomography ([Fig. 5C ]) can help distinguish between neurofibroma and neurofibromatosis based on the number
of lesions present.
Malignant Peripheral Nerve Sheath Tumor
Pathology
Malignant peripheral nerve sheath tumors are rare, accounting for ∼ 3 to 10% of all
soft tissue sarcomas. These tumors are highly malignant with a strong tendency for
local recurrence and distant metastasis. In 25 to 50% of cases, MPNSTs are associated
with NF1, the most significant risk factor for their development. Among NF1 patients,
deep-seated plexiform neurofibromas carry the highest risk for malignant transformation.[42 ]
Imaging
On US, MPNSTs typically appear as irregularly shaped masses with a heterogeneous internal
echotexture, infiltrative borders, and disruption of normal fascicular architecture.
Magnetic resonance imaging often reveals heterogeneous lesions with an iso- to hypointense
signal on T1-weighted images relative to muscle and a hyperintense signal on T2-weighted
images. Following intravenous gadolinium administration, MPNSTs exhibit marked, often
irregular or nodular enhancement. Peritumoral soft tissue edema is a common associated
finding.[43 ]
Traumatic Neuroma
Pathology
Traumatic neuromas are hyperplastic reparative proliferations of peripheral nerves
that develop following injury, and they typically present as nodular soft tissue masses.
Clinically, they most often manifest with painful hypersensitivity and a positive
Hoffmann-Tinel sign.[44 ] Based on the mechanism of injury, traumatic neuromas are classified into two primary
types: terminal neuromas and neuromas-in-continuity. The latter can result from either
total or partial nerve transection or from repetitive blunt trauma. Fusiform neuromas
are commonly seen following nerve transection, particularly involving the digital
nerves.[44 ]
Imaging
On US, traumatic neuromas appear as well-defined hypoechoic or mixed-echogenicity
nodules located along the expected course of the affected nerve.[45 ] Magnetic resonance imaging typically demonstrates these lesions as isointense to
skeletal muscle on T1-weighted images, hyperintense on T2-weighted sequences, with
contrast enhancement following intravenous gadolinium administration.[45 ]
Tumors of Uncertain Differentiation
Synovial Sarcoma
Pathology
The term synovial in synovial sarcoma is a misnomer because the tumor does not arise from synovial
tissue. Instead, those sarcomas are categorized as mesenchymal spindle cell tumors
displaying varying degrees of epithelial differentiation.[46 ]
[47 ] Soft tissue sarcomas are rare malignant tumors, accounting for < 1% of newly diagnosed
cancers annually. Approximately 60% of soft tissue sarcomas arise in the extremities,
with 15 to 25% affecting the upper limb and only 5 to 10% involving the hand or wrist.[48 ]
Although synovial sarcoma can occur at any age, it most commonly affects children
and young adults, with a peak incidence in the fourth decade of life.[46 ] Early diagnosis is often challenging because the clinical symptoms of synovial sarcoma
are nonspecific and can mimic benign conditions such as trauma, myositis, bursitis,
or tendinitis, frequently leading to misdiagnosis. The initial growth is often slow,
and some patients also report long-standing pain at the site of the tumor before the
appearance of noticeable swelling.[46 ]
[49 ] The imaging characteristics of synovial sarcomas are variable, ranging from nonaggressive
to more aggressive features.[47 ] Due to their typically small initial size (often < 5 cm), gradual growth, and well-defined
margins, these lesions are sometimes misclassified as benign.[47 ] Making an early diagnosis is pivotal. Patients with advanced synovial sarcoma have
a poor prognosis compared with those presenting with local disease.[46 ]
Imaging
On radiographs, ∼ 30% of synovial sarcomas demonstrate calcifications that often appear
in an eccentric or peripheral distribution relative to the soft tissue mass. The presence
of fine stippled calcifications can be considered suspicious for synovial sarcoma.[47 ] On MRI ([Fig. 6 ]), small synovial sarcomas may appear relatively homogeneous, demonstrating marked
hyperintensity on T2-weighted fat-suppressed sequences and hypointensity on T1-weighted
images.
Fig. 6 Synovial sarcoma. A 24-year-old patient with a painless, slowly growing mass on the
volar aspect of the wrist. (A ) Magnetic resonance imaging demonstrates a well-defined, markedly hyperintense lesion
(encircled) on proton-density-weighted images and (B ) a hypointense signal on T1-weighted images. (C ) There is strong contrast enhancement following intravenous gadolinium administration.
This imaging profile can closely resemble benign entities such as ganglia or synovial
cysts, posing a significant diagnostic pitfall. However, following intravenous gadolinium
administration, synovial sarcomas usually exhibit prominent and heterogeneous contrast
enhancement, aiding in differentiation from benign lesions.[28 ] Typical imaging signs, such as the “triple sign,” referring to pronounced heterogeneity
on T2-weighted images, and the “bowl-of-grapes sign,” characterized by features such
as hemorrhage and fluid-fluid levels, are often absent when synovial sarcoma occurs
in the hand, further complicating the diagnosis.[47 ]
Metastases
Pathology
Metastases of the hands are exceedingly rare, accounting for ∼ 0.1% of all metastatic
lesions. These metastases may present with nonspecific symptoms, such as pain, tenderness,
palpable masses, and ulceration, that can lead to misdiagnosis as infectious or inflammatory
conditions, thereby delaying appropriate treatment.[50 ]
[51 ] In a descriptive study published in 2021, Cattelan and Dumontier reviewed 337 studies
comprising 452 cases of hand metastases. The most common primary tumor was lung cancer
(40%), followed by gastrointestinal, genitourinary, gynecologic, and ear, nose, and
throat malignancies. Of the reported cases, 59% involved osseous metastases; 31% were
soft tissue metastases.[52 ] Acral metastases generally carry a poor prognosis because they typically reflect
widespread disease dissemination. The mean survival following the diagnosis of hand
metastasis was reported to be ∼ 7 months[51 ]
[52 ] ([Fig. 6A, B ]).
Imaging
Metastases usually appear as osteolysis on radiography ([Fig. 7A ]) and less frequently as osteoblastic lesions (e.g., in prostate cancer). The distal
phalanges are more frequently affected due to their greater blood supply. On MRI ([Fig. 7B ]), metastases differ from normal bone marrow in their signal intensity. Magnetic
resonance imaging is particularly useful for evaluating extraosseous metastatic components.
Fig. 7 Metastasis of adenocarcinoma of the lung. A 65-year-old patient with a history of
recurrent tenosynovitis of both hands presents to an orthopedic specialist after experiencing
a sudden onset of sharp, severe pain in the right hand while performing household
activities. (A ) Dorsovolar radiography reveals a pathologic fracture of the second metacarpal. (B ) Subsequent magnetic resonance imaging demonstrates a 3 × 2 × 2-cm lesion located
in the metadiaphysis of the second metacarpal (arrow), with a substantial extraosseous
soft tissue component. Histopathologic analysis confirmed the lesion to be a metastasis
from a moderate to poorly differentiated adenocarcinoma of the lung.
Tumor-simulating Lesions (Pseudotumors)
Lobular Capillary Hemangioma
Pathology
Lobular capillary hemangioma is a benign, rapidly growing vascular proliferation that
manifests on the skin, the subcutaneous tissue, or the mucous membranes.[53 ]
[54 ] The often used term pyogenic granuloma is a misnomer because the condition is neither pyogenic nor granulomatous. Histologically,
it consists of clusters of hyperplastic capillaries separated by a lobule containing
a central feeder vessel.[54 ] Clinically, it is a smooth, red to purple, sessile or pedunculated lesion. There
is a history of rapid growth, usually a few weeks.[53 ] Common complications are bleeding and ulceration.[54 ]
The exact etiology is unknown; however, theories about the underlying cause are minor
trauma, chronic wounds, and viral infections.[53 ] The occurrence of lobular capillary hemangioma in the finger is more commonly associated
with trauma than occurrence at other sites.[54 ] The treatment options are surgical excision, cryotherapy, curettage, laser, sclerotherapy,
and microembolization. Most cases require therapy, and only a few may resolve spontaneously.
A wide range of recurrence rates between 3.7% and 43.5% have been described.[53 ] Of the different treatment options, surgical management shows the lowest recurrence
rate.[53 ]
Imaging
On US ([Fig. 8 ]), lobular capillary hemangioma is a heterogeneous, mainly hypoechoic, well-defined
mass with abundant blood flow signals within the lesion on color Doppler flow.[55 ]
Fig. 8 Lobular capillary hemangioma. A 15-year-old patient presents with an exophytic mass
on the volar aspect of the middle finger of the right hand. The lesion had developed
rapidly 2 months ago following minor (bagatelle) trauma. (A ) Photograph showing a pulp, or “berry,” located on the volar side of the middle finger.
(B, C ) On ultrasound, the mass appeared as a sharply demarcated, slightly inhomogeneous
lesion (B, arrow) with pronounced internal vascularization (C).
Gout
Pathology
Gout is the most common cause of inflammatory arthritis in both men and women, with
a rapidly increasing incidence attributed to the global rise in associated conditions,
such as obesity, insulin resistance and metabolic syndrome, hypertension, and chronic
kidney disease. Over recent decades, the incidence of gout has tripled.[56 ]
[57 ] The disease progresses through several stages: initial asymptomatic hyperuricemia,
followed by acute gout flares characterized by marked pain and inflammation, and,
if inadequately managed, chronic tophaceous gout develops.[58 ]
The gold standard for diagnosis remains the identification of monosodium urate (MSU)
crystals in synovial fluid using polarized light microscopy. However, this method
has limitations, including the technical difficulty of joint aspiration, especially
in small joints, and the potential for false-negative results in up to 25% of cases.
In addition, MSU crystals can deposit in extra-articular soft tissues such as tendons
and ligaments.[58 ]
Imaging
Ultrasound can depict the three principal components of tophi: the central crystal
and debris core, the surrounding fibrovascular matrix, and the peripheral granulation
tissue. The tophi present as well-circumscribed lesions containing bright echogenic
crystals interspersed with hypoechoic septa that may demonstrate internal vascularity
on Doppler imaging. The surrounding granulation tissue is typically seen as a hypoechoic
halo.[57 ]
[59 ]
On radiographs, tophi appear as high-attenuation soft tissue foci. On conventional
computed tomography (CT), tophi appear as nodules or masses with a density of ∼ 160
to 170 HU, lower than that of typical calcifications. However, internal calcium deposition
can lead to inhomogeneous density, making differentiation from other calcified lesions
challenging on standard CT.[58 ] Dual-energy computed tomography (DECT) allows accurate identification of MSU crystal
deposition, confirming the diagnosis of gout. The tophi appear as dense soft tissue
lesions with MSU deposits that by definition are color-coded green.[59 ] Dual-energy computed tomography is highly specific and effective across all phases
of gout, although its sensitivity may be reduced in early-stage disease.[58 ]
Rheumatoid Nodules
Pathology
Rheumatoid arthritis is a chronic systemic autoimmune disease characterized by synovial
inflammation. Rheumatoid nodules are subcutaneous masses that occur in up to 35% of
patients over the course of the disease.[60 ] These nodules most commonly develop over extensor surfaces and pressure points,
including the fingers, hands, and elbows.[58 ]
Imaging
On US, rheumatoid nodules appear as oval homogeneously hypoechoic masses that are
closely associated with the bone surface.[61 ] On MRI, they demonstrate iso- to hypointense signal on T1-weighted images relative
to skeletal muscle, with variable T2 signal intensity depending on the degree of necrosis.
Following intravenous gadolinium administration, enhancement may vary depending on
the lesion's internal composition.[62 ]
The Role of Tumor Centers
According to the 2023 ESSR guidelines, referral to a specialized sarcoma treatment
center is recommended for any patient who presents with a soft tissue tumor measuring
≥ 5 cm that demonstrates indeterminant or suspicious findings on US or MRI, or in
cases with a clinical suspicion of malignancy. Importantly, patients suspected of
having a sarcoma should be referred to a sarcoma reference center before undergoing
biopsy or surgical intervention. Early referral helps prevent diagnostic delays and
unplanned excisions, commonly referred to as “whoops procedures.” Biopsy of suspected
appendicular soft tissue sarcomas should be performed by a radiologist with tumor
expertise, using image-guided techniques. In cases where surgery has been performed
without prior referral, patients must be promptly directed to a sarcoma center for
further evaluation and appropriate management.[4 ]
