Narrative review of chest wall ultrasound: a practical approach

Introduction

The thoracic wall constitutes a crucial anatomical region housing various pathological conditions that lead to frequent consultations in all levels of healthcare (1). Among these, traumatically derived pathologies are particularly prevalent. Traditionally, initial assessments rely on plain radiography, especially in emergency scenarios; however, its diagnostic capacity is often constrained. When conventional methods prove inadequate, escalating to more sensitive yet costly modalities like computed tomography (CT) or, less commonly, magnetic resonance imaging (MRI) becomes necessary (1,2).

In recent years, ultrasound has emerged as a valuable diagnostic tool for evaluating chest wall pathology. Its popularity can be attributed to several factors, including its excellent diagnostic capacity, particularly for superficial pathologies such as those located in the chest wall. Moreover, it is widely available throughout the healthcare system, including emergency departments and intensive care units, where patient mobilization can be complex. Finally, it is an inexpensive option compared to other imaging techniques, such as CT or MRI, and does not involve ionizing radiation, unlike CT or X-rays.

Ultrasound, when performed as a targeted examination focusing on the problematic area, is commonly referred to as point-of-care ultrasound (POCUS). This approach has demonstrated its efficacy in routine medical practice, delivering quick, affordable, secure, and accurate diagnoses across all levels of healthcare (3). As the landscape of diagnostic imaging continues to evolve, understanding the expanding role of ultrasound in thoracic wall pathology becomes imperative for healthcare practitioners seeking efficient and comprehensive diagnostic solutions. We present this article in accordance with the Narrative Review reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-355/rc).

Methods

The search strategy and methods are reported in Table 1.

Indications

Due to its superficial location, ultrasound serves as a highly valuable “point-of-care” examination for evaluating chest wall pathology. It encompasses five primary indications (4): assessing localized pain, typically following trauma; evaluating abnormal palpations and chest wall swelling; serving as an excellent first-line investigation for soft tissue tumors (5); providing specific clarification for uncertain results from other imaging techniques, such as the evaluation of possible foreign bodies visualized on X-ray (6); guiding biopsies and interventions.

However, the method is not without limitations, including interobserver and interequipment variability, technical challenges in cases of obesity or subcutaneous emphysema, and inferior global overview capability in assessing all the chest wall and deeper thoracic structures compared to CT and MRI (7). Despite these constraints, ultrasound offers noteworthy advantages, including cost-effectiveness, accessibility, tolerability, and safety. It also excels in differentiating between cysts and homogeneous solid masses (5).

Technique

A high-frequency linear array (>10 MHz) is imperative for optimal chest wall visualization, while lower-frequency transducers (5–10 MHz), both linear and curved, may prove beneficial in specific scenarios such as examinations involving obese or muscular patients, as well as deep-seated or large lesions (8-10). The ultrasound device should be equipped, at a minimum, with color Doppler, as evaluating the vascularization of lesions provides highly valuable information in some differential diagnosis (5,9,10). Employing more advanced Doppler techniques, such as power Doppler, is advisable due to its superior sensitivity in detecting low-velocity vascular flows, thereby enhancing diagnostic capabilities (10,11). Additionally, the availability of panoramic or extended imaging options is recommended to provide a comprehensive view of larger lesions, encompassing their morphology and relationships with adjacent structures (5,10).

Lesions must be addressed in at least two orthogonal planes, with care taken to avoid excessive transducer pressure, particularly when assessing vascularization. Excessive pressure may lead to vessel collapse, potentially yielding a false impression of absent vascularization (5,10). The use of abundant gel reduces transducer pressure, optimizing skin contact and preventing air artifacts resulting from a poor probe-gel interface; this is particularly useful when assessing tumours that protrude prominently from the chest wall. Comparing opposite sides of the chest wall is also very useful to resolve unclear findings.

Regarding patient positioning, a supine position is typically required for evaluating the anterior chest wall, while the posterior and lateral sides are commonly assessed with the patient in a sitting position (12).

Ultrasound interpretation should not rely solely on images; a fundamental aspect of the examination involves obtaining a comprehensive clinical history, particularly when addressing lesions with suspected tumor characteristics. Key questions to inquire include: when did you first notice the lesion? Is the size of the lesion increasing or diminishing? Does the mass hurt? Has there been trauma or intervention in the past (5,9,10)?

Normal anatomy

The ultrasound evaluation of the chest wall includes the examination of the skin, subcutaneous fatty tissue, muscles, bony and joint structures, as well as intercostal spaces (12). The assessment of the breast is beyond the scope of this review; however, it is crucial to distinguish between extramammary and intramammary lesions that may require specialized attention (13).

Spanning from the cutaneous surface to the pleura, the exploration encompasses various components (Figure 1):

• Skin: visualized as a slender hyperechoic line. Potential findings may necessitate the use of dermatologist-grade probes (14).
• Subcutaneous fat tissue: manifests as lobes of hypoechoic fat separated by echogenic septa. The thickness of the subcutaneous tissue is determined by the examined area and the patient’s body mass index.
• Muscles: displayed as hypoechoic, uniform structures with intermittent linear echogenic images.
• Bone structures: typically, only the anterior face (superficial cortex) is observable, represented by an echogenic line and a posterior acoustic shadow. Ultrasonography allows for the evaluation of the superficial aspects of the ribs, costal cartilage, costochondral junction, sternum, scapula, clavicle, and, to a lesser extent, vertebral bodies (spinous processes). It is important to note that ultrasound cannot reliably assess deeper or medullary abnormalities within these bone structures.
• Joints: ultrasound serves as a valuable tool for joint assessment, enabling the detection of inflammatory activity through power Doppler or microvascular flow imaging (MVFI) and the identification of synovial growth, joint effusion, and osteophytes.
• Intercostal spaces: ultrasound facilitates a detailed exploration of intercostal spaces, particularly relevant when a patient reports pain or the presence of a mass.

Figure 1 Panoramic ultrasound view depicting normal chest wall anatomy. S, skin; SF, subcutaneous fat layer; F, fascia; M, muscle (serratus anterior); R, rib; IC, intercostal space; P, pleura; L, lung.

Anatomic variants

Chest wall structures exhibit numerous normal variants, some common and others rare. While generally clinically insignificant, they can prompt patient consultation, often presenting as a painless palpable mass (8). Unfamiliarity with these variations may result in misdiagnosis and unnecessary additional examinations.

Common anomalies involve alterations in rib convexity (15), calcification of costal cartilage—prevalent in healthy middle-aged and elderly individuals—and subluxation of the clavicular head. Other less frequent abnormalities include bifid, fused, or hypoplastic ribs, which are a more common reason for consultation in pediatric patients (16) (Figures 2,3).

Figure 2 Rib convexity asymmetry. A 22-year-old woman with no medical history reports a left thoracic mass. Ultrasound is performed over the area of the mass. An asymmetry in the convexity of the ribs is evidenced. The left rib (B) protrudes more than the right rib (A), as demonstrated by the difference in distance between the chondrosternal junction and the cutaneous surface (shown by the double arrows). (C) A contrast-enhanced thoracic CT scan of the same patient performed for another reason shows the asymmetry of the convexity (indicated by the arrows). CT, computed tomography.

Figure 3 Calcifications of the costal cartilage. (A-C) Different calcifications of the costal cartilage in various patients (indicated by the arrows).

Sternal deformities, including anterior angulation or elongation of the xiphoid process, are very frequent reasons for consultation and ultrasound requests due to central thoracic mass palpation (17) (Figure 4). Pectus excavatum or pectus carinatum, though common, seldom necessitate radiological or ultrasound studies (18).

Figure 4 Xiphoid process angulation. A 73-year-old man presents with a lump and discomfort in the epigastric region. (A) US panoramic view (rotated 90° to the right for better understanding) reveals that the lump corresponds to the tip of the xiphoid process (arrows), which angles anteriorly, causing the palpable lump. Otherwise, the study is unremarkable. (B) Sagittal plane MIP reconstruction from a chest CT (performed for other reasons) clearly shows the anterior angulation of the sternal xiphoid process (arrow). US, ultrasound; MIP, maximum intensity projection; CT, computed tomography.

Less common findings include the sternal foramen, occasionally mistaken for a fracture, pseudoxiphoid sternal foramen or prominent manubrial cleft (17). Accessory muscles, such as accessory pectoralis major or minor, are usually incidental findings rather than consultation prompts (19). The absence of the pectoralis major muscle, indicative of Poland Syndrome, is an infrequent occurrence (18).

Chest wall pathology

Trauma

Rib fractures are prevalent, constituting 50% of injuries in blunt thoracic trauma (7). Ultrasound significantly enhances the sensitivity of rib fracture detection compared to X-rays, as demonstrated by Gilbertson and colleagues in a meta-analysis (20). In both emergency and radiologist-performed scenarios, ultrasound exhibited an average sensitivity of 89.3% and specificity of 98.4%, surpassing X-ray accuracy when compared to CT (the gold standard). It should be emphasized that in traumatic emergency situations, the confirmation or exclusion of associated injuries, such as pneumothorax or hemothorax, holds greater significance than the diagnosis of fractures itself, an area where ultrasound also proves to be particularly effective (7,21).

Acute fractures are identifiable on ultrasound by cortical disruption or irregularity in the anterior hyperechoic bone–soft tissue interface of the ribs. Gilbertson demonstrated that cortical disruption is the most critical sign for the detection of rib fractures (positive likelihood ratio of 55.7) (20). Other accompanying signs of fractures include soft tissue swelling and hematoma, often clearly correlated with the site of maximum tenderness (8) (Figure 5).

Figure 5 Rib fracture. A 54-year-old woman. Sudden chest pain following a sudden movement. (A) Ultrasound over the point of maximum pain shows disruption of the cortex of the 9th right rib (arrow). (B) Doppler ultrasound study shows no significant activity but reveals a small hematoma (arrowhead) adjacent to the fracture (arrow). (C) X-ray in AP rib projection (right) shows no findings. R, right; AP, antero-posterior.

Costochondral junction and costal cartilage fractures present similar findings to rib fractures, even though the largest series published by Malghem et al. (22), with only 15 chondral injuries, demonstrated lower diagnostic accuracy for US compared to CT, detecting only 20% of them. Caution is warranted near the costochondral joint, where small steps might mimic fractures (8,23).

Evolved rib fractures manifest as pseudonodular images with pronounced posterior acoustic shadows, representing bone callus. In the initial stages, increased vascularity may be observed in power Doppler studies (Figure 6).

Figure 6 Rib fracture. A 36-year-old male with a history of a motorcycle accident one month ago, presenting with persistent pain in the right posterior thoracic wall. (A) X-ray in AP rib projection (right) shows no findings. (B) Targeted ultrasound study over the painful area on the right posterior rib cage. An area of cortical irregularity (arrow) is identified at the 10th rib consistent with a callus from a rib fracture. AP, antero-posterior.

Fractures involving other bony structures of the chest wall (clavicle, scapula, sternum, and vertebral spinous processes) exhibit similar findings to those of ribs (Figure 7). However, the complete characterization of fractures in these bones is very limited with ultrasound evaluation. This limitation is particularly relevant in sternal fractures, posing specific diagnostic challenges. Sternal fractures, which typically occur in the context of high-energy thoracic trauma (typically car accidents) (7), can be detected sonographically by the disruption of the anterior bone cortex. However, ultrasound will be highly limited for evaluating the posterior cortex (underestimating bone displacements) as well as the mediastinal injuries that may be associated. Therefore, if a sternal fracture is suspected or identified using ultrasound, it is advisable to expand the study with a CT scan (24).

Figure 7 Clavicular fracture. A 75-year-old male with shoulder pain and hematoma following a fall two weeks ago. (A) Panoramic view of the clavicle shows a proximal cortical disruption (arrow) adjacent to the sternoclavicular joint (arrowhead), consistent with clavicular fracture. (B) Chest CT scan done posteriorly to accurately characterize the fracture shows a multifragmentary proximal clavicular fracture. It is important to note the limitations of ultrasound in evaluating the posterior cortex and, generally, the features of bone fractures. CT, computed tomography.

Hematomas, whether located in the subcutaneous fatty layer or in the intramuscular space, appear as heterogeneous collections of variable size, often poorly defined, with no vascularity observed in color Doppler studies. They are typically preceded by trauma, surgeries, or altered coagulation states. Evolving hematomas may show septations or increased echogenicity and occasional calcification (organized hematoma). Hematomas usually resolve in 6–8 weeks, depending on size and patient coagulation status (4,9). Sarcomas and other malignant lesions may initially manifest as hematomas; therefore, it is advisable to reassess them if they fail to resolve within a reasonable time frame or if the hematoma is unexpected (for instance, when there is no precedent trauma).

Muscle injuries in the chest wall, though infrequent, include notable cases of pectoralis major musculotendinous rupture, often associated with sports practices such as weightlifting or wrestling. Ultrasound typically shows either partial or complete distal tendon ruptures or, less commonly, disruption of the muscle’s proximal thoracic origin. Acute phases exhibit hematoma and perifascial fluid, while chronic injuries show fibrosis, muscular adhesions, retraction and atrophy, with increased echogenicity indicating fat infiltration (8).

Infections

Ultrasound proves to be a valuable tool for studying infectious pathology. The most prevalent infection of chest wall is cellulitis, where ultrasound reveals features such as increased echogenicity and thickness of subcutaneous fat accompanied by hyperemia observed in color Doppler (25). However, these ultrasound findings are not exclusive indicators of cellulitis, as similar appearances can manifest in various non-infectious conditions. Therefore, a thorough clinical context is crucial for accurate diagnosis (8).

Another frequent indication for ultrasound is the detection of abscesses, presenting as liquid collections with ill-defined contours, surrounded by vessels in power Doppler studies. Clinical symptoms, including pain, redness, and swelling, often raise suspicion of a chest wall abscess (9). Ultrasonography plays a role in assessing the extent of the process, its relationship to adjacent structures, and guiding punctures for microbiological diagnosis. The sonomorphology of abscesses can vary significantly based on their stage. If there is a suspicion of involvement of deep planes with fasciitis or pyomyositis, it is advisable to expand the study with other techniques such as CT or MRI.

While septic arthritis of the sternoclavicular joint is rare in immunocompetent patients, it constitutes 17% of septic arthritis cases in immunocompromised individuals (25). Ultrasound becomes a valuable tool in such cases where the presence of joint effusion, in alignment with clinical indicators, raises a high suspicion of septic arthritis. Finally, it is also important to consider that intrathoracic infectious processes may extend to involve the structures of the chest wall. In such cases, it is advisable to complete the study with a CT scan.

Tumors

Ultrasonography is an excellent imaging technique for assessing any superficial soft-tissue mass (5,9). A part from previously discussed advantages (availability, cost and lack of ionizing radiations), US outstands particularly in the characterization of soft-tissue masses because of its reasonably robust diagnostic capabilities. Two prospective studies by Hung and Griffith et al. (26,27) established that around three-quarters of soft tissue tumors could be confidently diagnosed by its US characteristics when performed by experienced radiologists. In fact, a correct diagnosis (confirmed with histology) was made in 95-96% of the cases where the radiologist was confident in the US diagnosis. Even further a study by Goldman et al. (28) argued that frequently, further MRI examination did not alter the original diagnosis or even narrow the differential diagnosis. According to this study 73% of initial diagnosis did not change in 92 patients retrospectively revised with initial US and subsequent MRI.

Benign and malignant soft tissue tumors typically present as painless masses, with benign lesions being notably more prevalent than malignant ones. Therefore, the pivotal consideration in evaluating a soft tissue mass lies in determining whether it is a benign lesion or a potentially malignant one, warranting further actions such as MRI and biopsy or even referral to a specialized center (5,10).

The systematic assessment required for an accurate diagnosis of any soft tissue mass should encompass various factors: location (superficial versus deep), dimensions, echogenicity, echotexture, shape, margins, and vascularization (evaluated through color Doppler or power Doppler) (27). Additionally, it is essential to provide a detailed description of the lesion’s anatomical relationships, as well as to evaluate the regional lymph nodes.

Benign tumors of the chest wall

Epidermoid cysts, also referred as sebaceous cysts or epidermal inclusion cysts, manifest as hypoechoic, well-defined round masses with posterior acoustic enhancement. In some cases, these cysts are linked to the skin through a small sinus. Echogenic foci or small internal calcifications, attributed to keratin or cholesterol deposition, could be identified. Internal Doppler flow is not typically evident, but these cysts may display “twinkling artifact” (5,9). This Doppler artifact, though not exclusive to epidermoid cysts, manifests as a focal display of alternating colors on the Doppler signal behind a reflective object, creating the illusion of turbulent blood flow (Figure 8).

Figure 8 Epidermoid cysts. (A) Well defined hypoechoic subcutaneous nodule, this example shows posterior acoustic enhancement and the characteristic (though not always present) connection sinus with the skin surface (arrow). (B) PD study of another epidermoid cyst. It exhibits the characteristic twinkling artefact (arrow). This epidermoid cyst also contains echogenic foci, which represent keratin and cholesterol deposits (arrowhead). PD, power Doppler.

Lipoma is the most prevalent chest wall tumor. These lesions manifest as well-defined, hypoechoic, hyperechoic, or isoechoic compressible nodules in comparison to surrounding fat tissue. They often display hyperechoic streaks inside, known as septae (9). Lipomas typically exhibit minimal to no vascularity. In fact, the identification of vessels may prompt suspicion of a potential low-grade liposarcoma. While these tumors may exhibit slow growth over an extended period (months to years), an accelerated growth rate, the presence of calcifications, the onset of symptoms, or any deviation from the typical appearance also raises concerns about the possibility of a low-grade liposarcoma (5,29) (Figure 9).

Figure 9 Lipoma. A 53-year-old woman with a non-painful, palpable lump in the intermammary sulcus, present for several years. (A) Ultrasound reveals a well-defined, large (5.5 cm) homogeneous nodular mass situated in the subcutaneous fatty tissue, isoechoic with surrounding fat, and displaying fine septations inside. No vascularity was observed in the color Doppler study (not shown). (B) MRI study of the same lesion (T1 sequence) confirms the fat composition and homogeneity of the lesion (indicated by the arrow). Surgical excision confirmed the diagnosis. MRI, magnetic resonance imaging.

Lymphatic or vascular malformations represent a broad and heterogeneous spectrum of lesions commonly misclassified as “hemangiomas”. Ultrasonography serves as an initial diagnostic tool, while magnetic resonance (MR) is the key modality for precise classification and treatment planning, accurately delineating their extension and anatomical relationships. On ultrasound, these lesions may display variable echogenicity compared to adjacent tissues, presenting as hyperechoic or hypoechoic masses with homogeneous or heterogeneous echostructure. They may exhibit cystic areas, dilated/tortuous vessels, and highly echogenic foci with posterior enhancement indicative of phleboliths. Color and pulsed Doppler studies are instrumental in discerning the arterial or venous nature of vascular malformations (30) (Figure 10).

Figure 10 Vascular malformation. An 86-year-old woman with a history of MALT lymphoma consults due to the presence of a subcutaneous nodule on the left rib cage. (A) Ultrasound on the lesion shows a well-defined nodular structure in the muscular plane, with septations inside. (B) Doppler study reveals a significant increase in vascularity. Pulsed-wave Doppler demonstrates the presence of arterial waveforms. The lesion suggests a high-flow vascular malformation (arterial component). Given the context, a biopsy was performed, ruling out malignancy, and subsequent follow-ups showed no changes. MALT, mucosa associated lymphoid tissue.

Elastofibroma dorsi. Reactive pseudotumor typically located near the lower scapula. While often asymptomatic, patients may report mass palpation and mild pain during movement. Ultrasound reveals a deep (beneath latissimus dorsi), non-encapsulated, heterogeneous lesion with a unique sonomorphology: “layered” curvilinear structures parallel to ribs, alternating hypoechoic (fibrous tissue) and hyperechoic lines (fatty tissue). Power Doppler studies show no significant vascularity. A contralateral study is advisable due to high bilaterality. Considering scapula obscuration on ultrasound, MRI or CT may be necessary in some cases (31) (Figure 11).

Figure 11 Elastofibroma dorsi. A 73-year-old woman presented with a large tumor in the right scapular region, particularly painful during movement. (A) Panoramic ultrasound view reveals a large and deep lesion (arrows) below the latissimus dorsi (arrowheads) and adjacent to the ribs, challenging to delineate, especially in its deeper aspects. (C,D) Detailed ultrasound images expose the lesion’s heterogeneity with alternating hypoechoic and hyperechoic areas. The arrow in (C) indicates the margin of the scapula. In (D), lines have been overlaid to better illustrate the characteristic laminar morphology of elastofibromas. (B,E) Offer detailed views from the pre-surgical MRI study of the same lesion (arrows indicating the lesion). (B) T2FatSat and (E) T1 images demonstrate the laminar morphology, showcasing alternating areas of fat and fibrous tissue in elastofibromas and its typical location (arrowheads depicting latissimus dorsi muscle). MRI, magnetic resonance imaging.

Neurogenic tumors encompass a diverse spectrum of lesions, predominantly benign but also including malignant forms. To better capture this diversity, the preferred nomenclature, in contrast to traditional terms like schwannoma, is peripheral nerve sheath tumors (PNST) and malignant PNST (MPNST). These lesions may arise in superficial or deep layers, notably the intercostal spaces of the chest wall, often accompanied by characteristic neurogenic pain. On ultrasound, they appear as round, well-defined, hypoechoic, vascularized lesions with peripheral nerve continuity, capable of abutting and displacing adjacent structures without invasion. Cystic and fatty degeneration may be observed. MPNST is more prevalent in type 1 neurofibromatosis patients. Lesions prompting consideration of MPNST exhibit poor definition, infiltration, or rapid growth (5,9) (Figure 12).

Figure 12 Peripheral nerve sheath tumor. A 47-year-old woman, complaining of a painful lump in the right axillary area. The pain radiates towards the arm and hand. (A) Well-defined hypoechoic and heterogeneous nodular lesion with an anterior fusiform extension (arrow). (B) Power Doppler study reveals internal vascularity and anterior and posterior extensions. The ultrasound findings, combined with the clinical presentation, strongly suggest a benign nerve sheath tumor. Pathological examination after surgical excision confirmed the diagnosis.

Fibromatoses are a group of fibroblastic and myofibroblastic proliferative entities that have comparable histological characteristics. They have a benign nature but can exhibit locally aggressive behavior. Although uncommon in the chest wall, they can present as palpable masses resulting in patient consultation. On ultrasonography, these lesions are often hypoechoic and fusiform, with moderate vascularity. A closer examination may reveal fascia continuity. MRI is frequently required for an accurate diagnosis, especially when certainty cannot be established through clinical history, as in post-surgical cases. It is also essential to accurately delineate anatomical relationships before surgery (5) (Figure 13).

Figure 13 Aggressive fibromatosis. A 25-year-old woman with a history of corrective surgery for winged scapula 10 years ago. For the past 6 months, she reports a gradually growing, palpable, and painful dorsal tumor. (A) POCUS in the surgical scar area shows a relatively well-defined hypoechoic lesion in the deep muscular plane with cystic areas inside (arrow). (B) Power Doppler study reveals increased vascularity. The ultrasound characteristics are suspicious, suggesting a fibromatous lesion (desmoid tumor) in this context. Percutaneous biopsy confirmed the diagnosis. (C-E) Display the presurgical MRI study (sequentially corresponding to T1, T2FS, and T1FS contrast enhanced sequences) of the lesion (arrows) confirming the solid nature of the lesion with avid contrast enhancement, but focal hypointense and non-enhancing areas inside indicative of fibrotic and/or cystic foci. POCUS, point-of-care ultrasound; MRI, magnetic resonance imaging; T2FS, T2 fat saturated; T1FS, T1 fat saturated.

Malignant tumors of the chest wall

Primary malignant tumors of the chest wall, such as malignant fibrous histiocytoma or dermatofibrosarcoma protuberans, are rare, with liposarcomas probably being the most prevalent among them (2). Chest wall metastases, though more common, usually arise in an already disseminated neoplastic process, posing minimal diagnostic challenge (Figures 14,15). Malignant solid soft tissue tumors typically appear as hypoechoic, often heterogeneous lesions, demonstrating rapid growth and exhibiting significant vascularity in color Doppler. In such cases, evaluation with MRI and subsequent biopsy is recommended for definitive diagnosis (4,5,9) (Figure 16). Another scenario to consider, although not very common, is the invasion of the thoracic wall by intrathoracic tumors. This typically occurs with primary lung neoplasms but can also involve pleural or mediastinal tumors (Figure 17).

Figure 14 MALT lymphoma. A 57-year-old woman with a history of MALT lymphoma, currently disease-free, notices a non-painful mass in the left infraclavicular region. (A) POCUS study. Well-defined hypoechoic nodule in the subcutaneous tissue of the upper anterior chest wall. (B) US power Doppler study reveals a marked increase in vascularity. Overall, the characteristics suggest a lesion suspicious of malignancy (hypoechoicity and increased vascularity), likely indicating recurrence of the lymphoma in this context. Biopsy of the lesion confirmed the diagnosis. (C) Restaging chest CT. The arrow marks the lesion previously explored with ultrasound. MALT, mucosa associated lymphoid tissue; POCUS, point-of-care ultrasound; US, ultrasound; CT, computed tomography.

Figure 15 Rib metastasis. A 75-year-old-male with a history of metastatic hepatocellular carcinoma (lung) reports pain in the left chest wall coinciding with a newly appearing mass. (A) Panoramic ultrasound view of the mass shows a large, well-defined, heterogeneous predominantly hypoechoic solid lesion located in a deep plane (intercostal space) protruding outward (arrow). (B) Power Doppler study demonstrates moderate vascularity. Cystic/necrotic areas are also observed within the lesion (arrow). Overall, the ultrasound features suggest a malignant lesion, and given the context the most likely possibility is a metastasis. (C) Thoracoabdominal contrast-enhanced CT for restaging reveals the solid lesion. It can be seen emerging from the 10th left rib (the arrow indicates the area of costal bone lysis). The lesion occupies the intercostal space, protruding both into the thoracoabdominal interior and towards the cutaneous surface. CT, computed tomography.

Figure 16 Dermatofibrosarcoma protuberans. A 42-year-old male. Non-painful palpable mass with several months of evolution in the right pectoral area. (A) Visible erythematous nodule upon visual inspection. (B) Oval hypoechoic and well-defined nodule located in the subcutaneous tissue of the chest wall. (C) The power Doppler study shows increased vascularity. All the characteristics suggested a lesion suspicious for malignancy. The biopsy confirmed the diagnosis of dermatofibrosarcoma protuberans.

Figure 17 A 69-year-old man with hemoptysis and chest pain. A contrast-enhanced thoracic CT scan is performed. (A) Axial images in lung window show a cavitated pulmonary mass (arrow). (B) Soft tissue window images show the infiltration of the mass into the bony and muscular planes of the chest wall (arrows). (C) Ultrasound performed for diagnostic biopsy guidance shows the large pulmonary mass (arrow) extending anteriorly into the chest wall and infiltrating the muscular plane (arrowheads). CT, computed tomography.

Tumor-like lesions

Fat necrosis is a benign inflammatory condition, usually a consequence of trauma, in which, following the death and rupture of adipocytes, saponification processes occur. Frequent and well-known in breast radiology, it can occur anywhere in the subcutaneous fat tissue of the body. The ultrasound appearance of fat necrosis is diverse and usually vague, showing as a poorly defined region with mixed echogenicity and nodular or pseudonodular hyper-, hypo-, or isoechoic nodules. Augmented Doppler activity may be recognized due to hyperemia. Given the variety in its appearance, effective interpretation is strongly reliant on patient’s medical history (9) (Figure 18).

Figure 18 Fat necrosis. A 60-year-old woman with a history of a traffic accident two months ago presents with persistent pain and palpable masses in the right dorsal wall. Ultrasound reveals pseudo-nodular, not well-defined hypoechoic images (arrows) within the subcutaneous fat. The surrounding fat appears slightly hyperechoic. Given the traumatic context, it is consistent with an area of post-traumatic fat necrosis.

Joint degeneration. Sternoclavicular joint degeneration is a common disorder that manifests as a painless soft tissue mass. Ultrasound reveals distinctive osteoarthritis signs, including capsular thickening, joint space narrowing, and osteophytes. Sternocostal and acromioclavicular joints are also often affected by osteoarthritis, and all of them are easily accessible for ultrasound examination (Figure 19).

Figure 19 Sternoclavicular joint osteoarthritis. A 77-year-old male. Non-painful palpable mass with several months of evolution is observed in the left upper chest. Ultrasound examination reveals degenerative changes in the sternoclavicular joint, including synovial distension (arrow) and a prominent osteophyte (arrowhead).

Ganglion cysts in the joint can also mimic a mass. On ultrasound, these cysts appear as anechoic uni- or multinodular lesions close to the joint that lack vascularization. It is possible to find debris or septae inside. When a connection with the joint is demonstrated, an immediate diagnosis can be made (8,9,32) (Figure 20).

Figure 20 Ganglion cyst. A 72-year-old female with a rapidly growing (within 1 month) palpable mass in the upper left shoulder and pain during shoulder mobilization. (A) Panoramic view of the lesion reveals a well-defined cystic nodule with debris in its interior, located adjacent to the acromioclavicular joint, which exhibited degenerative changes. (B) A detailed view of the same lesion. The white arrow depicts the connection of the lesion with the joint. The findings are consistent with an acromioclavicular ganglion cyst.

Lymphadenopathy often leads to consultation. An enlarged lymph node with an echogenic hilum, a regular hypoechoic cortex, and hilar blood flow is usually classified as reactive. In contrast, an enlarged lymph node with a spherical shape, no echogenic hilum, or a non-uniform cortex, along with peripheral blood flow, is considered suspicious of malignancy (9) (Figure 21).

Figure 21 Ultrasound of lymphadenopathy in different patients. (A) Ultrasound of a normal lymph node. Size <1 cm, thin cortex, no focal cortical thickening, and preserved fatty hilum (arrow). (B) Lymph node with intermediate characteristics. Measuring <1 cm and preserving the fatty hilum, but its cortex exhibited several nodular thickenings (arrows). Given the neoplastic context, a FNAB was performed, which was negative for malignancy. (C) Lymph node with clear characteristics of malignancy. Completely nodular and hypoechoic with loss of the fatty hilum, which is entirely replaced by parenchyma. This was a patient with newly diagnosed breast cancer, and the FNAB was positive. FNAB, fine-needle aspiration biopsy.

Future directions, new tools for advanced ultrasound

In recent years, new tools for advanced ultrasound have emerged, poised to enhance the diagnostic capabilities of traditional ultrasound (B-mode and Doppler ultrasound). The most promising among them are contrast-enhanced ultrasound (CEUS) (33) and elastography (34).

CEUS involves the administration of intravenous contrast, typically composed of gas microbubbles surrounded by a protective shell. Its goal is to assess vascularization and blood flow distribution in the body tissues. The importance of vascularization is well-known for differentiating various tissues, especially in distinguishing malignant from benign lesions, as neoangiogenesis and increased vascularization are typical phenomena in many tumors. In fact, this principle is the same underlying Doppler ultrasound, as well as contrasts used in MRI and CT scans. There is growing evidence of CEUS’s ability to assess solid lesions in other organs such as the liver, kidneys, or breast, and even some recent studies on soft tissue tumors (35). CEUS allows for a rapid, inexpensive, real-time evaluation of vascularization and is not contraindicated in patients with allergies to other contrasts (iodinated or gadolinium) or in patients with claustrophobia or metallic implants or pacemakers that contraindicate MRI. Although the evidence is still limited, it is likely to become a routine clinical tool in the future, complementing other diagnostic techniques for evaluating thoracic wall lesions. Finally, CEUS has also shown promise as a complementary technique to improve the precision of percutaneous biopsy (36).

Elastography, on the other hand, is a technique that aims to assess tissue stiffness. From a technical standpoint, there are two major elastography methodologies: strain elastography and shear wave elastography. While it is not the objective to analyze technical details extensively, the main difference between them lies in the method of generating stiffness maps. In strain elastography, the origin is the pressure applied by the transducer to induce changes in tissue shape, whereas shear wave elastography relies on generating shear waves from the transducer and generating stiffness maps from that. The main diagnostic principle behind elastography is that different tissues have different stiffness, with malignant tumors generally being stiffer than benign ones. There are also promising results regarding its use for diagnosing different organs and pathologies, including the assessment of soft tissue tumors (37). Its main advantage over CEUS is that it does not involve contrast administration, but on the downside, it is more sensitive to technique-related alterations. It also requires more evidence for standardized use in routine clinical practice but is another promising ultrasound technique with significant future potential.

Conclusions

Ultrasound is an excellent first-line technique for the evaluation of the thoracic wall. Whether in primary care or in challenging scenarios such as emergencies or the ICU, this technique often allows us to reach definitive diagnoses or at the very least guide the case for further management. In this sense, even more important than positively recognizing the typical characteristics of different pathologies is recognizing when we are dealing with atypical lesions or those with suspicious features. In such cases, where we cannot confidently diagnose, additional tests should be conducted to achieve a definitive diagnosis. This is particularly crucial for lesions suspected of malignancy. In order to achieve this, the article has reviewed the normal anatomy of the thoracic wall, along with the typical appearance of the main pathologies and suspicious features affecting this anatomical area.

Acknowledgments

Funding: None.

Footnote

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