Soft Tissue Masses of the Hand: A Review of Clinical Presentation and Imaging Features

More than 15% of all soft-tissue tumors arise in the hand. Because of the location of these tumors, even small abnormalities may be alarming to patients on presentation. Although the majority of lesions are benign and can be diagnosed solely by history and physical examination, additional imaging workup may be required to confirm a diagnosis or define anatomic extent of involvement. This paper aims to review the basic epidemiology, clinical presentation, imaging findings, and treatment options of the more common soft-tissue tumors of the hand.


Introduction
Of all soft-tissue tumors, more than 15%, surprisingly, arise in the hands, which comprise a total of only 2% of total body surface area [1]. Soft-tissue structures such as muscle, fat, tendons, blood vessels, and nerves derive from mesodermal mesenchyme throughout the body. Due to the superficial location, most hand tumors present early and can be easily visualized and palpated upon physical examination. Although 95% of softtissue tumors of the hand excluding the skin are benign and thus have a good prognosis, patients tend to be alarmed by even small abnormalities [2]. Malignant tumors are rare yet reflect 2% of all hand lesions and have unique characteristics.
Despite the ability to diagnose many of these lesions solely by history and physical examination, additional imaging workup may be required to confirm a diagnosis or define anatomic extent of involvement. Thus, radiologists serve an important role in aiding clinicians in the appropriate management of these conditions. This paper provides an overview of the basic epidemiology, clinical presentation, imaging findings, and treatment options of the more common soft-tissue tumors of the hand. often as men [4]. The most common location of ganglion cysts is the dorsal wrist (70%), with the volar wrist (~20%) and volar retinacular cysts (~10%) making up the majority of the remaining common locations.
Although mostly idiopathic in nature, a recent study demonstrated that at least 10% of patients report a preceding traumatic event before the appearance of a ganglion [5]. This coincides with popular agreement that repetitive stretching of the capsular and ligamentous structures around joints stimulates production of tissue hyaluronic acid by nearby fibroblasts [6]. Small rents in the communicating joint capsule permit accumulation of synovial fluid within the ganglion. Dorsal wrist ganglion cysts usually originate from the scapholunate joint ( Figure 1) while volar-based ganglion cysts originate from the radioscaphoid-scapholunate interval but can arise from the scaphotrapezial joint as well. Retinacular cysts along the finger flexor tendon sheaths most often arise at the A1 and A2 pulley [7] (Figure 2). Ganglion and synovial cysts are histologically distinct but radiologically indistinguishable and clinically treated equivalently. The myxoid degeneration of the connective tissue of the joint capsule leads to the formation of the ganglion cysts, which contain gelatinous fluid, including hyaluronic acid and mucopolysaccharides. They also have a fibrous lining [7][8][9], in contrast to synovial cysts that are lined with cuboidal epithelium and contain synovial fluid [7,8].

Imaging Appearance
Radiographic and advanced imaging are rarely indicated as the diagnosis of ganglion cysts is typically a clinical one. When obtained, plain radiographs may show associated soft-tissue swelling, but are generally unremarkable. MRI typically shows unilocular or multilocular T2 hyperintense cysts, and careful scrutiny of the adjacent joint capsule often reveals a pathognomonic communicating neck. If symptomatic, wrist ganglia are often amenable to ultrasound-guided needle fenestration and aspiration, though recurrence rates have been reported to be as high as 33-70% [10][11][12]. Aspiration with the injection of steroid does not significantly alter the recurrence rate [12,13]. Although not truly ganglion cysts, mucoid cysts of the distal interphalangeal (DIP) joints are common ( Figure 3) and are associated with osteoarthritis and marginal osteophytes (Heberden's nodes).
urr. Oncol. 2023, 30 wrist, consistent with dorsal ganglion. (D) Same dorsal hand mass on a T2-flu quence that appropriately loses signal intensity, consistent with dorsal ganglion.  (C) Transverse ultrasound at the palmar aspect of the small finger MCP joint in a different patient demonstrates a medial approach for an ultrasound-guided percutaneous needle decompression (arrow) of an A1 pulley retinacular cyst; note safe distance of the needle tip from the flexor tendon (*).

Clinical Features
The second most common masses of the hand are tenosynovial giant-cell tumors (TGCTs), historically also known as giant-cell tumors of tendon sheath, or pigmented villonodular synovitis (PVNS) when intra-articular. The global incidence is estimated to be around 43 cases per one million people [14]. These tumors affect patients between the age of 30 and 50 years old, with the median age around 47 years [14,15]. Classically, they present as a single nodule (localized) or as multiple nodules diffusely spread along the tendon sheath, or with pain and swelling of the joint when intra-articular. The most common location is the volar surface of the radial three digits near the distal interphalangeal joints of these fingers [16].
TGCTs are neoplasms, characterized by rearrangements of CSF1 which cause overexpression of macrophage colony-stimulating factor (CSF1) [17] This drives tumor growth, recruitment of non-neoplastic mononuclear and multinucleated inflammatory cells, and benign proliferation of the synovium in the tendon sheath. While non-metastasizing, these tumors may behave aggressively, and recent development of targeted anti-CSF1 agents has enabled systemic treatment options in addition to surgical resection [18].

Imaging Appearance
Radiographs may show erosion of adjacent bones or even joint destruction depending on the size and duration of presence of the lesion. However, 95% of patients present with radiographs that may only show soft-tissue swelling [15].
Advanced imaging is helpful in delineating the extent of disease and severity of adjacent bone or articular damage. Ultrasound typically depicts a heterogeneous hypoechoic mass with internal vascularity on Doppler interrogation. Dynamic ultrasound shows no

Clinical Features
The second most common masses of the hand are tenosynovial giant-cell tumors (TGCTs), historically also known as giant-cell tumors of tendon sheath, or pigmented villonodular synovitis (PVNS) when intra-articular. The global incidence is estimated to be around 43 cases per one million people [14]. These tumors affect patients between the age of 30 and 50 years old, with the median age around 47 years [14,15]. Classically, they present as a single nodule (localized) or as multiple nodules diffusely spread along the tendon sheath, or with pain and swelling of the joint when intra-articular. The most common location is the volar surface of the radial three digits near the distal interphalangeal joints of these fingers [16].
TGCTs are neoplasms, characterized by rearrangements of CSF1 which cause overexpression of macrophage colony-stimulating factor (CSF1) [17] This drives tumor growth, recruitment of non-neoplastic mononuclear and multinucleated inflammatory cells, and benign proliferation of the synovium in the tendon sheath. While non-metastasizing, these tumors may behave aggressively, and recent development of targeted anti-CSF1 agents has enabled systemic treatment options in addition to surgical resection [18].

Imaging Appearance
Radiographs may show erosion of adjacent bones or even joint destruction depending on the size and duration of presence of the lesion. However, 95% of patients present with radiographs that may only show soft-tissue swelling [15].
Advanced imaging is helpful in delineating the extent of disease and severity of adjacent bone or articular damage. Ultrasound typically depicts a heterogeneous hypoechoic mass with internal vascularity on Doppler interrogation. Dynamic ultrasound shows no movement of the mass during passive movement of the surrounding tendons. If localized, MRI reveals a heterogeneously T1 and T2 hypointense mass that enhances after intravenous contrast administration [19]. These tumors are often associated with intralesional hemorrhage and hemosiderin deposition; because hemosiderin includes paramagnetic Fe+3 atoms, the local magnetic field around areas of hemosiderin deposition become distorted, resulting in "blooming" artifacts on gradient-echo or susceptibility-weighted sequences ( Figure 4). This effect may be particularly pronounced in diffuse intra-articular forms of disease.
Curr. Oncol. 2023, 30 2036 movement of the mass during passive movement of the surrounding tendons. If localized, MRI reveals a heterogeneously T1 and T2 hypointense mass that enhances after intravenous contrast administration [19]. These tumors are often associated with intralesional hemorrhage and hemosiderin deposition; because hemosiderin includes paramagnetic Fe+3 atoms, the local magnetic field around areas of hemosiderin deposition become distorted, resulting in "blooming" artifacts on gradient-echo or susceptibility-weighted sequences ( Figure 4). This effect may be particularly pronounced in diffuse intra-articular forms of disease.

Clinical Features
Although the most common soft-tissue tumor of the body, lipomas of the hand are relatively uncommon, accounting for 8% of benign tumors of the hand [20,21]. Adipocytic tumors are commonly associated with translocations and rearrangements of the 12q13-15 chromosomal region [22]. It is believed that these abnormal karyotypes lead to chromosomal fusion products which promote proliferation of adipocytes. They also result in the upregulation of MDM2, an oncogenic signature of atypical lipomatous tumor (ALT)/welldifferentiated liposarcoma, with ALT being the preferred term for tumors in the extremities. Biologic transformation of ALT to dedifferentiated liposarcoma arises rarely but only after further genomic instability and generation of neochromosomes [23].
Lipomas of the hand present as slowly enlarging, soft non-tender masses. Symptoms of compression neuropathy can be present if the lesion is in the vicinity of peripheral nerves (e.g., carpal tunnel or Guyon's canal). On examination, a mobile mass with a characteristic "doughy" texture is the classic description. To differentiate from ganglion cysts, lipomas do not transilluminate. A positive Tinel's sign over the tumor can confirm adjacent nerve compression as the source of paresthesia.

Radiographic Appearance
On plain radiographs, an area of radiolucency within the soft tissues may be noted, and smooth scalloping of adjacent bones may be observed. Ultrasound examination will

Clinical Features
Although the most common soft-tissue tumor of the body, lipomas of the hand are relatively uncommon, accounting for 8% of benign tumors of the hand [20,21]. Adipocytic tumors are commonly associated with translocations and rearrangements of the 12q13-15 chromosomal region [22]. It is believed that these abnormal karyotypes lead to chromosomal fusion products which promote proliferation of adipocytes. They also result in the upregulation of MDM2, an oncogenic signature of atypical lipomatous tumor (ALT)/welldifferentiated liposarcoma, with ALT being the preferred term for tumors in the extremities. Biologic transformation of ALT to dedifferentiated liposarcoma arises rarely but only after further genomic instability and generation of neochromosomes [23].
Lipomas of the hand present as slowly enlarging, soft non-tender masses. Symptoms of compression neuropathy can be present if the lesion is in the vicinity of peripheral nerves (e.g., carpal tunnel or Guyon's canal). On examination, a mobile mass with a characteristic "doughy" texture is the classic description. To differentiate from ganglion cysts, lipomas do not transilluminate. A positive Tinel's sign over the tumor can confirm adjacent nerve compression as the source of paresthesia.

Radiographic Appearance
On plain radiographs, an area of radiolucency within the soft tissues may be noted, and smooth scalloping of adjacent bones may be observed. Ultrasound examination will reveal a well-circumscribed lesion that is homogenous and often hyperechoic in nature, although lipoma echogenicity is variable [24]. Magnetic resonance imaging will show a mass that has the same signal characteristics of subcutaneous fat tissue ( Figure 5). The mass may be well-demarcated with a fibrous pseudocapsule, but can also be poorly marginated, rendering it occult on imaging. Typically, low-grade lipomatous neoplasms do not enhance with contrast, although the fibrous pseudocapsule may show mild enhancement.
Curr. Oncol. 2023, 30 2 reveal a well-circumscribed lesion that is homogenous and often hyperechoic in natu although lipoma echogenicity is variable [24]. Magnetic resonance imaging will show mass that has the same signal characteristics of subcutaneous fat tissue ( Figure 5). T mass may be well-demarcated with a fibrous pseudocapsule, but can also be poorly m ginated, rendering it occult on imaging. Typically, low-grade lipomatous neoplasms not enhance with contrast, although the fibrous pseudocapsule may show mild enhan ment.

Clinical Features
These are the most common benign tumors of peripheral nerves, making up ab 5% of all benign soft-tissue neoplasms [25]. They are derived from Schwann cells and m elin sheaths and are well-encapsulated and slow-growing [26]. These tumors rarely volve the nerves of the hand and as benign tumors, malignant transformation is exc tional [27]. These tumors can present at any age, with an increased frequency particula within the third and sixth decades of life, and there is no gender predilection [26]. Th tumors often present as a painful mass, often with Tinel sign, and with careful excisi the peripheral nerve can be spared.

Radiographic Appearance
Schwannomas show low-signal intensity on T1W images and may display a "tar sign" appearance on fluid-sensitive sequences with central hypointensity and periphe hyperintensity, owing to collagenous and myxomatous components, respectively ( Fig  6) [28]. While schwannomas are eccentrically located allowing excision with nerve vage, they are often not radiologically distinguishable from neurofibromas [29]. MRI a aids in surgical planning to ensure optimum nerve recovery and minimize unnecess nerve damage during resection of the tumor.

Clinical Features
These are the most common benign tumors of peripheral nerves, making up about 5% of all benign soft-tissue neoplasms [25]. They are derived from Schwann cells and myelin sheaths and are well-encapsulated and slow-growing [26]. These tumors rarely involve the nerves of the hand and as benign tumors, malignant transformation is exceptional [27]. These tumors can present at any age, with an increased frequency particularly within the third and sixth decades of life, and there is no gender predilection [26]. These tumors often present as a painful mass, often with Tinel sign, and with careful excision, the peripheral nerve can be spared.

Radiographic Appearance
Schwannomas show low-signal intensity on T1W images and may display a "target sign" appearance on fluid-sensitive sequences with central hypointensity and peripheral hyperintensity, owing to collagenous and myxomatous components, respectively ( Figure 6) [28]. While schwannomas are eccentrically located allowing excision with nerve salvage, they are often not radiologically distinguishable from neurofibromas [29]. MRI also aids in surgical planning to ensure optimum nerve recovery and minimize unnecessary nerve damage during resection of the tumor. Figure 6. Patient with neurofibromatosis type II and mass in the third webspace of the hand. T2weighted axial image showing a round hyperintense mass (arrow) with a central region of low signal intensity (*), characteristic of peripheral nerve sheath tumor, in this case a schwannoma of the common digital nerve. The hypointense central portion in T2-weighted images is attributable to a dense area of collagenous stroma; when this collagenous region is larger, the mass may assume a "target sign" appearance.

Clinical Features
Glomus tumors are defined as perivascular neoplasms of the glomus body of the distal phalanx and subungual region. Most are benign, but some can be malignant and demonstrate aggressive behavior. The glomus body of the finger is a neuroarterial structure responsible for thermoregulation and is located underneath the nails or in the pulp of the finger. Accounting for about 1-5% of tumors in the hand, they generally present between the fourth and sixth decade of life [30]. Solitary glomus tumors are slightly more common in females than males. The etiology of many glomus tumors is idiopathic, although up to half harbor NOTCH-gene fusions, and BRAF mutations in a smaller subset [31,32].
Subungual and phalangeal glomus tumors tend to be less than 1 cm in size and present with the classic triad of symptoms: local sensitivity, pain with cold exposure, and severe pain following minor trauma [33]. Because of its rarity and miniscule size, the typical time from onset of symptoms to a correct diagnosis is around seven years [34]. Subungual involvement can lead to discoloration or deformation of the nail plate.

Imaging Appearance
Plain radiographic imaging of a glomus tumor is usually unremarkable. Rarely, cortical scalloping of the underlying phalanx can be found in long-standing cases. Ultrasound studies typically show hypoechogenicity, internal vascularity on Doppler interrogation, and tenderness to direct sonographic palpation with the ultrasound prob [35,36]. On MRI, glomus tumors manifest as smooth-contoured lesions, with low or intermediate signal on T1W images, with hyperintensity on T2W images (Figure 7) [37]. Because of the vascularity of the lesions, these lesions display characteristic uniform and avid contrast enhancement. Figure 6. Patient with neurofibromatosis type II and mass in the third webspace of the hand. T2weighted axial image showing a round hyperintense mass (arrow) with a central region of low signal intensity (*), characteristic of peripheral nerve sheath tumor, in this case a schwannoma of the common digital nerve. The hypointense central portion in T2-weighted images is attributable to a dense area of collagenous stroma; when this collagenous region is larger, the mass may assume a "target sign" appearance.

Clinical Features
Glomus tumors are defined as perivascular neoplasms of the glomus body of the distal phalanx and subungual region. Most are benign, but some can be malignant and demonstrate aggressive behavior. The glomus body of the finger is a neuroarterial structure responsible for thermoregulation and is located underneath the nails or in the pulp of the finger. Accounting for about 1-5% of tumors in the hand, they generally present between the fourth and sixth decade of life [30]. Solitary glomus tumors are slightly more common in females than males. The etiology of many glomus tumors is idiopathic, although up to half harbor NOTCH-gene fusions, and BRAF mutations in a smaller subset [31,32].
Subungual and phalangeal glomus tumors tend to be less than 1 cm in size and present with the classic triad of symptoms: local sensitivity, pain with cold exposure, and severe pain following minor trauma [33]. Because of its rarity and miniscule size, the typical time from onset of symptoms to a correct diagnosis is around seven years [34]. Subungual involvement can lead to discoloration or deformation of the nail plate.

Imaging Appearance
Plain radiographic imaging of a glomus tumor is usually unremarkable. Rarely, cortical scalloping of the underlying phalanx can be found in long-standing cases. Ultrasound studies typically show hypoechogenicity, internal vascularity on Doppler interrogation, and tenderness to direct sonographic palpation with the ultrasound prob [35,36]. On MRI, glomus tumors manifest as smooth-contoured lesions, with low or intermediate signal on T1W images, with hyperintensity on T2W images (Figure 7) [37]. Because of the vascularity of the lesions, these lesions display characteristic uniform and avid contrast enhancement.

Clinical Features
Low-flow malformations include venous malformations (VMs), capillary malformations (CMs), and lymphatic or venolymphatic malformations (LMs or VLMs) [38]. Arteriovenous malformations (AVMs) are the classic type of high-flow lesions that are commonly a result of prior trauma or invasive procedures within the hand. Historically in the radiology literature and in clinical practice, it is common to see the term "hemangioma" used to describe venous malformations.
The most common presentation of VMs is that of a soft-tissue mass that is painful with activity or cold weather. On examination, these soft-tissue masses usually have a bluish tint and increase in size with dependent positioning, while decompressing when the upper extremity is elevated due to changes in hydrostatic pressure. The lesions may cause compression of nearby nerves and corresponding paresthesia, pain, or weakness.
LMs have a classic rubber texture on palpation and can have overlying skin dimpling. Distinction from VMs can be made because LMs do not change in size based on the position of the upper extremity. Radiologic distinction can be difficult, particularly as some entities contain components of both as a venolymphatic malformation. CMs present as red or pink cutaneous discolorations that are commonly referred to as port-wine stains. Finally, AVMs are often warm, pulsatile masses that have associated bruits and thrills on examination due to arterialized blood flow through engorged veins. A proximal AVM may result in symptoms of digital ischemia and finger discoloration. Similar to LMs and CMs, AVMs do not change in size based on the position of the upper extremity  [38]. Arteriovenous malformations (AVMs) are the classic type of high-flow lesions that are commonly a result of prior trauma or invasive procedures within the hand. Historically in the radiology literature and in clinical practice, it is common to see the term "hemangioma" used to describe venous malformations.
The most common presentation of VMs is that of a soft-tissue mass that is painful with activity or cold weather. On examination, these soft-tissue masses usually have a bluish tint and increase in size with dependent positioning, while decompressing when the upper extremity is elevated due to changes in hydrostatic pressure. The lesions may cause compression of nearby nerves and corresponding paresthesia, pain, or weakness.
LMs have a classic rubber texture on palpation and can have overlying skin dimpling. Distinction from VMs can be made because LMs do not change in size based on the position of the upper extremity. Radiologic distinction can be difficult, particularly as some entities contain components of both as a venolymphatic malformation. CMs present as red or pink cutaneous discolorations that are commonly referred to as port-wine stains. Finally, AVMs are often warm, pulsatile masses that have associated bruits and thrills on examination due to arterialized blood flow through engorged veins. A proximal AVM may result in symptoms of digital ischemia and finger discoloration. Similar to LMs and CMs, AVMs do not change in size based on the position of the upper extremity 2.6.2. Imaging Appearance Plain radiographs of low-flow VMs may show phleboliths, pathognomonic calcifications within thrombosed veins, in the area of suspicion. These phleboliths will be hyperechoic on ultrasound, or can result in signal void on MRI (Figure 8). Sonographic imaging demonstrates a hypoechoic mass with monophasic low-velocity flow.

Imaging Appearance
Plain radiographs of low-flow VMs may show phleboliths, pathognomonic calcifications within thrombosed veins, in the area of suspicion. These phleboliths will be hyperechoic on ultrasound, or can result in signal void on MRI (Figure 8). Sonographic imaging demonstrates a hypoechoic mass with monophasic low-velocity flow.
Finally, ultrasound and color Doppler ultrasound can reliably assess the pulse flow characteristics of an AVM. CT angiography and venography is helpful in delineating the enlarged veins with arterialized flow (Figure 9). MRI imaging demonstrates tubular structures with flow voids on both T1W and T2W imaging [39]. Time-resolved MR angiography may be of use to help demonstrate early-draining veins, outline the location of shunts, and delineate the extent of collateral vasculature.   Finally, ultrasound and color Doppler ultrasound can reliably assess the pulse flow characteristics of an AVM. CT angiography and venography is helpful in delineating the enlarged veins with arterialized flow (Figure 9). MRI imaging demonstrates tubular structures with flow voids on both T1W and T2W imaging [39]. Time-resolved MR angiography may be of use to help demonstrate early-draining veins, outline the location of shunts, and delineate the extent of collateral vasculature.
Curr. Oncol. 2023, 30 2040 2.6.2. Imaging Appearance Plain radiographs of low-flow VMs may show phleboliths, pathognomonic calcifications within thrombosed veins, in the area of suspicion. These phleboliths will be hyperechoic on ultrasound, or can result in signal void on MRI (Figure 8). Sonographic imaging demonstrates a hypoechoic mass with monophasic low-velocity flow.
Finally, ultrasound and color Doppler ultrasound can reliably assess the pulse flow characteristics of an AVM. CT angiography and venography is helpful in delineating the enlarged veins with arterialized flow (Figure 9). MRI imaging demonstrates tubular structures with flow voids on both T1W and T2W imaging [39]. Time-resolved MR angiography may be of use to help demonstrate early-draining veins, outline the location of shunts, and delineate the extent of collateral vasculature.

Clinical Features
Superficial palmar fibromatosis of the hand, also known as Dupuytren's disease, is a connective-tissue disorder that results in firm, subcutaneous nodules on the palmar surface of the hand that can cause debilitating flexion contractures. Known as the "Disease of the Vikings", there is a strong predilection towards Caucasian males of northern European descent, with an incidence of roughly 30 per 100,000 annually [35]. In general, men are affected more than women at a ratio of about 2:142, and hereditary forms have been described [35].
Characteristic nodules and cords along the palmar fascia are thought to result from dysregulated fibroblastic proliferation mediated by fibrogenic cytokines: fibroblast growth factor, wingless/integrated (Wnt), and transforming growth factor β have all been implicated [36,40]. Disease most commonly affects the ring and small finger, but can affect any digit of the hand, typically starting in the palm and progressing distally [41]. Depending on the severity of disease, there may be overlying skin dimpling and pitting.

Imaging Appearance
Plain radiographs generally add little value in the imaging of palmar fibromatosis. On ultrasound, hypoechoic nodules that arise from the palmar fascia are characteristic. MRI reveals low-signal intensity both on T1W and T2W images, a common theme of lesions that are of composed of dense collagen. Intermediate signal intensity on T2W MRI suggests higher cellularity and a higher tendency towards recurrence [42]. Recent MRI studies have shown that T2 mapping can be used to quantify the extent of lesion collagenization in response to treatment and maturation [43] (Figure 10).

Clinical Features
Synovial chondromatosis is a rare benign neoplasm that generally affects patients in their fourth through sixth decades [44]. The disease more commonly occurs within the larger joints of the knee, hip, and shoulder. Pain, swelling, and decreased range of motion of the affected joint are some of the clinical symptoms. Recently, gene rearrangements involving FN1 and/or ACVR2A were detected in a majority of cases [45]. Superficial palmar fibromatosis of the hand, also known as Dupuytren's disease, is a connective-tissue disorder that results in firm, subcutaneous nodules on the palmar surface of the hand that can cause debilitating flexion contractures. Known as the "Disease of the Vikings", there is a strong predilection towards Caucasian males of northern European descent, with an incidence of roughly 30 per 100,000 annually [35]. In general, men are affected more than women at a ratio of about 2:142, and hereditary forms have been described [35].
Characteristic nodules and cords along the palmar fascia are thought to result from dysregulated fibroblastic proliferation mediated by fibrogenic cytokines: fibroblast growth factor, wingless/integrated (Wnt), and transforming growth factor β have all been implicated [36,40]. Disease most commonly affects the ring and small finger, but can affect any digit of the hand, typically starting in the palm and progressing distally [41]. Depending on the severity of disease, there may be overlying skin dimpling and pitting.

Imaging Appearance
Plain radiographs generally add little value in the imaging of palmar fibromatosis. On ultrasound, hypoechoic nodules that arise from the palmar fascia are characteristic. MRI reveals low-signal intensity both on T1W and T2W images, a common theme of lesions that are of composed of dense collagen. Intermediate signal intensity on T2W MRI suggests higher cellularity and a higher tendency towards recurrence [42]. Recent MRI studies have shown that T2 mapping can be used to quantify the extent of lesion collagenization in response to treatment and maturation [43] (Figure 10).

Imaging Appearance
Some 70-95% of synovial chondromatosis cases display multiple intra-articular calcifications [44]. The "ring-and-arc" mineralization pattern recapitulates the lobular morphology of enchondral ossification observed in cartilaginous tumors. Synovial chondromatosis may result in scalloping and extrinsic erosion of bone on both sides of the involved joint, usually best depicted on CT or MRI. On T2-weighted MRI, noncalcified areas of neoplastic hyaline cartilage show high intensity [45] (Figure 11). Synovial chondromatosis is a rare benign neoplasm that generally affects patients in their fourth through sixth decades [44]. The disease more commonly occurs within the larger joints of the knee, hip, and shoulder. Pain, swelling, and decreased range of motion of the affected joint are some of the clinical symptoms. Recently, gene rearrangements involving FN1 and/or ACVR2A were detected in a majority of cases [45].

Imaging Appearance
Some 70-95% of synovial chondromatosis cases display multiple intra-articular calcifications [44]. The "ring-and-arc" mineralization pattern recapitulates the lobular morphology of enchondral ossification observed in cartilaginous tumors. Synovial chondromatosis may result in scalloping and extrinsic erosion of bone on both sides of the involved joint, usually best depicted on CT or MRI. On T2-weighted MRI, noncalcified areas of neoplastic hyaline cartilage show high intensity [45] (Figure 11).

Clinical Features
Tenosynovitis is the inflammation of the tendon sheath and is an orthopedic emergency when caused by infection [46]. Because of its structure as a fluid within a closed compartment, the tendon sheath is susceptible to significant damage in the setting of increased compartment pressures. Other more common causes include inflammation and trauma. The most common location of infectious tenosynovitis is the flexor tendon sheaths as a result of trauma in the skin [47].
Infectious tenosynovitis can lead to irreversible disability and morbidity due to the resulting contracture of involved musculature. Common microorganisms in order of prevalence include Staphylococcus aureus, Pasteurella multocida (cat bites), Neisseria

Clinical Features
Tenosynovitis is the inflammation of the tendon sheath and is an orthopedic emergency when caused by infection [46]. Because of its structure as a fluid within a closed compartment, the tendon sheath is susceptible to significant damage in the setting of increased compartment pressures. Other more common causes include inflammation and trauma. The most common location of infectious tenosynovitis is the flexor tendon sheaths as a result of trauma in the skin [47].
Infectious tenosynovitis can lead to irreversible disability and morbidity due to the resulting contracture of involved musculature. Common microorganisms in order of prevalence include Staphylococcus aureus, Pasteurella multocida (cat bites), Neisseria gonorrhoeae (sexually transmitted), Eikenella corrodens (human bites), and Mycobacteria tuberculosis [48].

Imaging Appearance
Due to its higher-contrast resolution, MRI is the most sensitive and specific imaging modality for the diagnosis of infectious tenosynovitis [46]. Fluid accumulation within the tendon sheaths and synovial hyperplasia can be detected on MRI. Especially in tenosynovitis caused by Mycobacteria tuberculosis, a nonspecific "rice-bodies" appearance may be seen. With gadolinium on contrast-enhanced MRI, the paratendinous contrast enhancement caused by diffuse inflammation can be demonstrated. In addition, CT with contrast demonstrates tendon thickening, edema, and abscess. Because hands are frequently used in daily activities, they are vulnerable to penetration and impalement injuries that result in foreign bodies in the hand. Foreign bodies may remain asymptomatic if initially overlooked, but over time may lead to inflammatory, allergic, and infectious complications [49]. Complications include foreign-body granulomas, pyogenic granulomas, abscess, chronic discharging wound, and impingement on neighboring bones, tendons, blood vessels, and nerves. Prevention of these complications consists of surgical removal.

Imaging Appearance
The index of suspicion for a foreign body should be high in any penetrating hand injury and warrants imaging investigation especially given a suggestive history [50]. Plain radiographs with multiple views should be the first-line imaging investigation. Ultrasound can detect non-radiopaque foreign bodies and assist in foreign-body removal (Figure 12). If a suspected foreign body is not found in other imaging modalities, CT and/or MRI may be helpful in identifying small wood or wood-like fragments and delineate the associated soft-tissue inflammation and other foreign-body complications.

Imaging Appearance
Due to its higher-contrast resolution, MRI is the most sensitive and specific imaging modality for the diagnosis of infectious tenosynovitis [46]. Fluid accumulation within the tendon sheaths and synovial hyperplasia can be detected on MRI. Especially in tenosynovitis caused by Mycobacteria tuberculosis, a nonspecific "rice-bodies" appearance may be seen. With gadolinium on contrast-enhanced MRI, the paratendinous contrast enhancement caused by diffuse inflammation can be demonstrated. In addition, CT with contrast demonstrates tendon thickening, edema, and abscess.

Clinical Features
Because hands are frequently used in daily activities, they are vulnerable to penetration and impalement injuries that result in foreign bodies in the hand. Foreign bodies may remain asymptomatic if initially overlooked, but over time may lead to inflammatory, allergic, and infectious complications [49]. Complications include foreign-body granulomas, pyogenic granulomas, abscess, chronic discharging wound, and impingement on neighboring bones, tendons, blood vessels, and nerves. Prevention of these complications consists of surgical removal.

Imaging Appearance
The index of suspicion for a foreign body should be high in any penetrating hand injury and warrants imaging investigation especially given a suggestive history [50]. Plain radiographs with multiple views should be the first-line imaging investigation. Ultrasound can detect non-radiopaque foreign bodies and assist in foreign-body removal (Figure 12). If a suspected foreign body is not found in other imaging modalities, CT and/or MRI may be helpful in identifying small wood or wood-like fragments and delineate the associated soft-tissue inflammation and other foreign-body complications.  The underlying extensor tendon (arrowheads) was confirmed to be normal at surgery.

Clinical Features
Of all soft-tissue sarcomas (STS), only about 20% originate in the upper extremity [2]. These soft-tissue tumors arise from extraskeletal mesenchymal tissues. In the pediatric population, fibrosarcomas and rhabdomyosarcomas are the most common hand softtissue sarcomas.
Epithelioid sarcomas, synovial sarcomas (Figure 13), and undifferentiated pleomorphic sarcomas represent the most common type of malignant soft-tissue sarcomas of the hand in adults [51]. Acral myxoinflammatory fibroblastic tumor is a lower-grade sarcoma with a predilection for the hand and fingers ( Figure 14). Typically, STS presents as a painless growing mass; patients may attribute incidental trauma to the area. a painless growing mass; patients may attribute incidental trauma to the area.
In the event of a diagnosis of a soft-tissue sarcoma, MRI is required to map anatomic involvement of the neuro-vasculature, tendons, and bone so that resectability can be determined, and appropriate reconstructive options can be planned. Typically, STS have low signal on T1W images and are heterogeneously high-signal intensity on T2 sequences. In higher-grade STS or carcinosarcoma, a non-enhancing necrotic center with peripheral enhancing zone of viable tumor may be observed (Figure 15), which can lead to mischaracterization as an abscess. Depending on tumor size and grade, appropriate staging studies need to be performed, which may include lymphoscintigraphy for those STS with a propensity to metastasize to nodes (e.g., epithelioid sarcoma). Figure 13. Synovial sarcoma. Fat-suppressed T2-weighted axial MR image of the wrist just proximal to the distal radioulnar joint shows a high-signal-intensity lobulated volar mass (arrow) deep to the superficial flexor tendons and overlying the pronator quadratus (*). Internal areas of necrosis and hemorrhage may lead to areas of signal heterogeneity due to evolving blood products within the tumor (arrowhead). Figure 13. Synovial sarcoma. Fat-suppressed T2-weighted axial MR image of the wrist just proximal to the distal radioulnar joint shows a high-signal-intensity lobulated volar mass (arrow) deep to the superficial flexor tendons and overlying the pronator quadratus (*). Internal areas of necrosis and hemorrhage may lead to areas of signal heterogeneity due to evolving blood products within the tumor (arrowhead).
In the event of a diagnosis of a soft-tissue sarcoma, MRI is required to map anatomic involvement of the neuro-vasculature, tendons, and bone so that resectability can be determined, and appropriate reconstructive options can be planned. Typically, STS have low signal on T1W images and are heterogeneously high-signal intensity on T2 sequences. In higher-grade STS or carcinosarcoma, a non-enhancing necrotic center with peripheral enhancing zone of viable tumor may be observed (Figure 15), which can lead to mischaracterization as an abscess. Depending on tumor size and grade, appropriate staging studies need to be performed, which may include lymphoscintigraphy for those STS with a propensity to metastasize to nodes (e.g., epithelioid sarcoma). , as well as smaller volar components (arrowhead). Initially, this was thought to be an abscess but was later revealed to be acral myxoinflammatory fibroblastic sarcoma after incisional biopsy, and ultimately required second and third ray amputations to achieve wide negative margins. , as well as smaller volar components (arrowhead). Initially, this was thought to be an abscess but was later revealed to be acral myxoinflammatory fibroblastic sarcoma after incisional biopsy, and ultimately required second and third ray amputations to achieve wide negative margins. Figure 14. A 67-year-old man with soft tissue mass of the hand. (A) Axial fat-suppressed PD MRI shows a large hyperintense soft-tissue mass in the dorsum of the hand, centered over the second and third metacarpals, and encasing the index finger extensor tendons (arrowhead), and thin tails of infiltrating tumor partially encasing middle finger extensor tendon (arrow). (B) Sagittal fat-suppressed PD MRI highlights the extent of the infiltrative mass along the index finger dorsally (arrows), as well as smaller volar components (arrowhead). Initially, this was thought to be an abscess but was later revealed to be acral myxoinflammatory fibroblastic sarcoma after incisional biopsy, and ultimately required second and third ray amputations to achieve wide negative margins.

Surgical Considerations
STS of the hand and fingers present unique challenges as input from multiple surgical subspecialists may be required, including orthopaedic oncology, hand surgery, and plastic surgery, in discussions with patients for goals of care and outcome expectations. The need to achieve wide negative tumor margins often necessitates radical resection with reconstruction of tendon, bone, nerve, and skin in pursuit of complete tumor extirpation, although ray amputation may ultimately be required for limb salvage [52,53]. Multidisciplinary planning with hand and plastic surgery is paramount in successful restoration of hand function and soft tissue coverage. Planned positive margins with adjuvant radiation may be acceptable in certain situations where local recurrence risk is outweighed by preservation of limb function [54], although outcomes in such cases are usually poor [55].

Discussion
Soft-tissue tumors of the hand are relatively commonly encountered in clinical practice. Although the vast majority of these lesions are benign, they may generate a great deal of anxiety for patients. Knowledge of the more common hand soft-tissue tumors, understanding their presentations, and recognizing their imaging characteristics can help radiologists and clinicians appropriately treat and advise patients. In this review, the complexity of the various soft-tissue tumors of the hand was synthesized and discussed. The basic epidemiology, clinical presentation, imaging findings, and treatment options of each tumor were highlighted. The overarching goal of the paper is to educate trainees, provide a reference to practicing physicians, and spread awareness about this topic. Institutional Review Board Statement: Ethical review and approval were waived because this project is not human subject research requiring IRB review, approval or oversight. This determination is based on the definition of "human subject" found at 45 CFR 36.102(e). This research does not involve interactions with living human subjects or accessing identifiable information or identifiable biospecimen, which does not meet the definition of human subject research.