Imaging of Soft-Tissue Pseudotumors: A Pictorial Review

Abstract

Soft-tissue pseudotumors are a myriad group of clinically palpable masses that mimic soft-tissue tumors. These mimickers may be misinterpreted as malignant sarcomas despite appropriate clinical and radiological evaluation, resulting in unwarranted interventions and a diagnosis of a pseudotumors is achieved only after histopathological evaluation. A systematic approach is needed to achieve a definitive diagnosis or to limit the differential diagnosis by using imaging in conjunction with clinical history, physical examination, and anatomical location. The objective of this article is to provide an overview of the imaging features of some of the most common soft-tissue pseudotumors. Recognition of these pseudotumors is of paramount importance as no further investigation or intervention may be required in majority of the cases.

Keywords

pseudotumors - soft-tissue mass - tumor mimic

Introduction

Various different pathologies can present as a soft-tissue mass clinically. Soft-tissue masses usually pose a diagnostic challenge as there are diverse group of lesions than can present as soft-tissue mass, comprising both neoplastic (benign and malignant) and non-neoplastic lesions. Numerous non-neoplastic pathological entities can mimic a soft-tissue neoplasm. Pseudotumors, or the tumor-mimicking lesions, are defined as palpable masses that produce tumor-like appearances on imaging.[1] Mimickers of soft-tissue tumors are ubiquitous as compared with true neoplastic lesions. These lesions constitute a diverse group, with variable etiology and histopathology, ranging from normal anatomical variants to posttraumatic lesions, cystic lesions, inflammatory and infectious lesions, metabolic disorders (crystal deposition disease and amyloidosis), non-neoplastic vascular lesions, and miscellaneous disorders.[2] Although some of these lesions may have distinctive imaging findings, imaging feature of several of the lesions is indeterminate. Imaging features in conjunction with location of the pathology supplemented by clinical presentation allow the radiologist to suggest an accurate diagnosis in majority cases. Despite similarity in imaging approach to all soft-tissue lesions, including both pseudotumors and “true” soft-tissue tumoral counterparts, further management of these lesions is different. Biopsy should be done only when imaging appearance is nonspecific and the diagnosis is indeterminate. Therefore, a radiologist plays an essential decisive role in the diagnosis and management of soft-tissue lesions ([Table 1).]

Table 1 Classification of various soft-tissue pseudotumors based on etiology

Soft-tissue pseudotumors
Infection	Inflammatory	Traumatic	Degenerative	Vascular	Miscellaneous
• Tuberculosis • Abscess	• Epidermal inclusion cyst • Tenosynovitis • Cellulitis	• Hematoma • Muscle tear • Morel-Lavallee lesion • Muscle hernia	• Ganglion cyst • Bursitis	• Arteriovenous malformation • Aneurysm and pseudoaneurysm	• Myositis ossificans • Foreign body granuloma • Pigmented villonodular synovitis

Infective

Infections are very often diagnosed clinically and imaging only acts as a supplementary tool. Infections are occasionally observed as a focal soft-tissue lesion that is not typical of an infective process and may pose confusion in diagnosis.

Tuberculosis

Musculoskeletal manifestations of tuberculosis are uncommon, and affect bones, joints, and soft tissue.[3] Slow growing clinically palpable swelling is the classical presentation. An ill-defined complex appearing mass is generally seen, either as a solid or a peripherally enhancing cystic collection ([Fig. 1]).

Fig. 1 A 12-year-old child with jaw tuberculosis who presented with left-sided face swelling for the last 3 months. (A) Orthopantomogram shows radiolucency (red arrow) on left side of mandible involving the mandibular third molar tooth bud. (B–D) Coronal and axial contrast computed tomography images show thickened heterogenous soft-tissue lesion in left cheek with underlying cortical breech in body and ramus of left mandible. Histopathological microphotograph (E) reveals granulomas comprising epitheloid cells, lymphocytes, and Langerhans giant cells (yellow arrow) confirm tubercular osteomyelitis.

Abscess

Superficial soft-tissue infections (dermatitis, cellulitis, and superficial abscess formation) are usually clinical diagnosis. Patients are febrile and present with a painful mass in association with evidence of infection in blood profile. Overlying skin changes may be seen on examination.

Ultrasound is an excellent tool to differentiate abscess from cellulitis that is seen as thick and echogenic adipose tissue with variable degrees of increased vascularity and nonloculated perifascial fluid collection. Abscesses are seen as fluid collections that may be well-defined or ill-defined and the contents may range from being anechoic to hyperechoic with surrounding inflammatory changes and raised peripheral vascularity ([Fig. 2]). The contents are usually mobile and can be observed with dynamic compression during real time ultrasound.

Fig. 2 A 11-year-old child with abscess who presented with swelling in distal thigh for the last 4 years. Radiograph (anteroposterior and lateral) right knee (A) reveals soft-tissue opacity (white arrow) with peripheral calcification in posteromedial aspect of distal right thigh. Grayscale and color Doppler ultrasound images (B, C) show a well-defined, hypoechoic lesion in subcutaneous plane with rim calcification and no internal vascularity. Coronal short tau inversion recovery (D), coronal proton density fat saturated (E), and axial post-contrast T1-weighted (F) magnetic resonance images reveal a well-defined, mildly peripherally enhancing lesion. Aspirate demonstrated thick exudative fluid consistent with pus (G).

Inflammatory

Epidermal Inclusion Cyst

Sonographically, epidermoid cysts are relatively well-circumscribed hypoechoic soft-tissue masses with smooth margins that show posterior acoustic enhancement and diffuse internal echoes giving pseudotestes appearance with absence of color signal on Doppler imaging[4] ([Fig. 3]). The margins become irregular and there is associated increase in vascularity in surrounding tissue in case of rupture. This may imitate an aggressive lesion and biopsy may be indispensable to exclude malignancy.

Fig. 3 A 22-year-old woman with epidermal cyst presented with painless palpable fluctuant swelling over xiphisternum. (A and C) Transverse ultrasound images reveal a well-circumscribed, rounded, hypoechoic soft-tissue lesion in subcutaneous plane with posterior acoustic enhancement (blue arrow) and lateral edge shadowing, containing multiple anechoic filiform bands (white arrow in C) within. The lesion is showing no vascularity on color Doppler (B). Diagnosis was made on the basis of typical sonographic appearance and confirmed on cytology (D).Wright Giemsa smear microphotograph(40x) showing calcification with interspersed anucleate and nucleated squames.

Traumatic

Hematoma

On ultrasonography, hematomas are generally irregular, ill-defined avascular collection. The echogenicity of hematomas evolves over time. Acute hematomas are generally well-defined and hyperechoic to hypoechoic ([Fig. 4]). As coagulation proceeds, echogenicity as well as the heterogeneity of hematomas increases. The evolution of a hematoma is marked by liquefaction and they then are visible as anechoic fluid collection. Magnetic resonance imaging (MRI) appearances are variable. Fluid–fluid levels may be seen and depending on the levels of methemoglobin and hemosiderin, the T1-weighted signal intensity may vary from hyperintensity to hypointensity. There may be considerable overlap in imaging findings of a hematoma and an aggressive tumor due to complex imaging appearance as a consequence of repeated hemorrhages.[5] Hematoma is the most common mimicker of a soft-tissue sarcoma.[6] Sarcomas may also demonstrate internal hemorrhage and present clinically as hematomas. The most important differentiating feature is evolution over time; a hematoma should resolve over weeks, whereas a sarcoma will persist or increase in size. Close monitoring with ultrasound to look for evolution is prudent. A biopsy should be considered in cases with no resolution or increase with time.

Fig. 4 Two patients with hematoma who presented with soft-tissue swelling with h/o trauma. (A) Transverse ultrasound images reveal ill-defined anechoic collection with multiple internal septae and echogenic debris within, showing no vascularity on color Doppler imaging (B). Diagnosis of a resolving hematoma was based on imaging appearance in conjunction with clinical presentation. Aspirate revealed 11 mL hemorrhagic fluid. In another patient with similar clinical presentation (C and D), grayscale and Doppler ultrasound images demonstrate large thick-walled cystic lesion with thick internal echoes and septae with layering (white arrow) suggestive of acute hematoma. Hematomas can vary in appearance depending on the stage of evolution.

Degenerative

Ganglion Cyst

Ganglion cysts are the most common soft-tissue lesions of the hand and wrist. They are frequently seen in periarticular location in relation to joint or a tendon sheath. The cyst is filled with mucin having fibrous capsule. The most common location is the dorsum of wrist in relation to scapholunate ligament (60–70% of cases).[7] A ganglion cyst on ultrasonography is visualized as an anechoic cystic lesion with well-defined smooth margins, lack of internal echoes, no internal flow, and increased through transmission ([Fig. 5]). The most important diagnostic feature is its relation with a joint or tendon sheath that is visible as a communication or neck, depicting the anatomic origin of the mass. Thus, anatomical location and classical imaging appearance are the clues that help reach the diagnosis in majority.

Fig. 5 A 40-year-old woman with ganglion cyst who presented with right wrist swelling for the last 2 years. (A and B) Grayscale and Doppler ultrasound images show a well-defined tiny anechoic cystic lesion with no internal echoes and septations showing no signal on color Doppler (B). Fine-needle aspiration cytology revealed ganglion cyst.

Vascular

Slow Flow Vascular Malformation

Vascular malformations comprise of one of the most common pseudotumors especially in pediatric age group.[8] These are divided into two main categories: low-flow vascular malformation (venous, lymphatic, capillary and mixed type) and high-flow vascular malformation (fistula and arteriovenous) on the basis of their hemodynamic characteristics.

They often present with skin discoloration. Venous malformations are the commonest vascular malformations that appear as focal saccular lesions or tubular collections of dilated vascular channels, often hypoechoic relative to the surrounding stroma. These lesions may be seen infiltrating subcutaneous fat, muscles, fascia, and tendons in the diffuse type or appear as a focal mass on sonography. Phleboliths are a distinctive feature and may be detected even on plain radiographs ([Fig. 6]). MRI is the most useful imaging modality for delineating the extent of the lesion and relation to the adjacent structures. Computed tomography (CT) can be of help in head and neck malformations.

Fig. 6 A 61-year-old woman with slow flow vascular malformation who presented with swelling over great toe for the last 6 years. (A and B) Anteroposterior and oblique radiograph left foot show soft-tissue opacity around first metatarsal and phalynx with few phleboliths (white arrow). (C–E) Grayscale and Doppler ultrasound images (E) show a well-defined round-to-ovoid hypoechoic lesion with irregular margins with multiple echogenic foci s/o phlebolith (yellow arrow) showing no significant vascularity on color Doppler (E). (F) Axial fat-saturated (FS), (G) coronal FS), (H) Cor T1, and (I) contrast magnetic resonance images show a well-defined lobulated soft-tissue lesion of altered signal intensity, isointense on T1, hyperintense on FS with delayed contrast enhancement.

Pseudoaneurysm

True aneurysms and posttraumatic pseudoaneurysms both can present as a focal mass and may mimic soft-tissue tumors. Pulsation artifact differentiates it from a solid mass.

On ultrasonography, they appear as a hypoechoic or anechoic mass with posterior acoustic enhancement. The internal echogenicity represents thrombus or septations. A pseudoaneurysm has a characteristic ying-yang sign appearance on color Doppler with to-and-fro waveform on spectral Doppler imaging representing bidirectional flow[9] ([Fig. 7]).

Fig. 7 A 40-year-old man with pseudoaneurysm who presented in emergency department. An incidental soft-tissue swelling noted over anterior abdominal wall in a middle-aged man undergoing Focused Assessment with Sonography in Trauma evaluation. Grayscale ultrasound images (A, B) reveal a well-defined, anechoic cystic lesion arising from a vessel and demonstrating bidirectional, turbulent, swirling blood flow pattern on color Doppler imaging (C, D) known as ying-yang sign. Diagnosis was made on the basis of typical color flow pattern of pseudoaneurysm.

Miscellaneous

Myositis Ossificans

During initial presentation at the time of onset, this entity can imitate soft-tissue tumors clinically and can be indistinguishable even on imaging and histology, especially in cases that lack history of trauma, leading to incorrect diagnoses and inappropriate treatment.[10] The characteristic appearance of myositis ossificans in the late stage is the formation of mature bone/ ossification within soft tissues. Imaging findings are variable and depend on the stage of presentation. Early imaging would reveal peripheral rim of calcification of the mass, 6 to 8 weeks after trauma ([Fig. 8]). After around 5 to 6 months, diffuse ossification and mature bone formation occur. Biopsy will confirm the presence of myofibroblasts and fibroblasts in late stages. Therefore, follow-up is pivotal in avoiding the detrimental misdiagnosis of soft-tissue tumor.

Fig. 8 A 19-year-old man presented with left proximal arm swelling for the last 3 months. Transverse ultrasound image (A) reveals markedly echogenic mass with shadowing indicative of calcification in muscle. Axial computed tomography images (B and C) show a well-defined, lobulated, bony lesion with typical dense peripheral calcification and central hypodensity in proximal metadiaphyseal region of left humerus. Magnetic resonance images reveal a well-defined juxtacortical lesion that appears isointense on T1-weighted (D), hyperintense on T2-weighted (E) images and shows no diffusion restriction on diffusion-weighted imaging and apparent diffusion coefficient map (F and G). Final diagnosis of myositis ossificans was made on the basis of imaging findings correlated with a history of trauma and confirmed on histopathology.

Foreign Body Granuloma

The imaging appearance of foreign body granuloma can be challenging. It can mimic a neoplasm in situations with chronic presentation, especially where the history of trauma is dubitable.

A proper patient history and clinical examination of the lesion help in narrowing down the differentials. Radiographs, ultrasound, CT, and MRI can identify the foreign body depending on its nature (wood, glass, etc.)

A foreign body granuloma can be identified as a low signal or signal void from foreign bodies with a characteristic ring-like reactive lesion on MRI, or an echogenic structure with posterior acoustic shadowing on ultrasound ([Fig. 9]).

Fig. 9 A 22-year-old woman presented with right hand swelling associated with h/o trauma 2 years back. Radiograph hand (A, B) reveals ill-defined soft-tissue opacity in first metacarpal space with a lytic lesion in shaft of first metacarpal, showing narrow zone of transition (yellow arrow). Ultrasound images (C, D) show a hyperechoic linear structure (black arrow) with no posterior acoustic shadowing suggestive of foreign body, and surrounding hypoechoic collection with no vascularity on color Doppler imaging (D) consistent with granulation tissue.

Conclusion

Diverse non-neoplastic pathologies can mimic a true soft-tissue neoplasm. It is important to recognize these pseudotumors on imaging to prevent unnecessary invasive procedures and additional anxiety to the patients. Knowledge of the normal anatomy, existence, and common imaging presentation of these pathological entities in conjunction with pertinent clinical findings (patient demographics, clinical history, anatomical location) enables the radiologist to make an accurate diagnosis in majority cases. A biopsy should be contemplated only in a clinically and radiologically indeterminate lesion to rule out an underlying malignancy.

Conflict of Interest

None declared.

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Publication History

Article published online:
09 January 2024