Role of USG in Thoracic Extrapulmonary Tuberculosis: Imaging Recommendations by the Society of Chest Imaging and Interventions

Keywords

tuberculosis - extrapulmonary - pleural - pericardial - ultrasonography - imaging

Introduction

Chest tuberculosis (TB) includes both pulmonary and extrapulmonary forms. In pulmonary TB (PTB), nodules, cavities, and consolidation are common forms of involvement. As expected, ultrasonography (USG) has limited utility in the evaluation of PTB due to the strong acoustic impedance of the aerated lungs. Although consolidation or collapse may be demonstrated, these findings lack specificity.[1] [2] [3] [4]

On the contrary, USG is a useful imaging investigation for evaluating extrapulmonary TB (EPTB) sites in the chest, especially in resource-constrained settings. These sites include the pleura, pericardium, chest wall, and, to a certain extent, the mediastinum. The use of USG for evaluation of these sites can aid in the initial diagnosis of TB, as well as follow-up. It has several advantages, including easy availability, rapidity, being radiation-free, not requiring sedation, and being a relatively economical imaging modality.[5] [6] [7]

Over the years, USG has evolved into a powerful diagnostic tool, bridging the gap between chest X-rays and other costlier investigations like computed tomography (CT) or magnetic resonance imaging (MRI). Furthermore, it helps ascertain the need for active interventions (e.g., drainage) and is immensely helpful during follow-up in many instances. The inclusion of USG in the diagnostic workup can therefore be instrumental in early diagnosis and prompt treatment, thereby improving patient outcomes.[1] [2] [3] [4] [5] [6] [7]

Methodology

The formulation of the Society of Chest Imaging and Interventions recommendations highlighting the role of USG in EPTB of the thorax was assigned to two experts, who then collated a multi-institutional team of specialists from across India. The initial work involved formulating key questions, which were later substantiated by a meticulous literature review of various sites of EPTB in the thorax with a special emphasis on the role of USG in their management. The directions for future research were also considered.

The recommendations are based on published literature and also consensus on the prevalent practice among thoracic radiologists drawn from multiple leading institutions across India. Each committee member focused on specific sites of EPTB in the thorax. The document comprised recommendations addressing critical questions regarding the role of USG in the management of EPTB in the thorax. The evidence levels adhered to the 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.[8] The recommendations were finalized after several online discussions and revisions.[8] Wherever available, a recommendation was made based on the level of evidence in published literature. The available literatures are provided in [Supplementary Table S1].

The manuscript is organized into sections for each EPTB site and discusses the recommended role, technique, and imaging findings/criteria as relevant, under the following sections.

We have arranged the discussion in four separate sections, where techniques, transducer selection, and findings are all discussed under the same section.

• Section 1: Mediastinum.

• Section 2: Pleura.

• Section 3: Pericardium.

• Section 4: Chest wall.

Section 1: Mediastinum

• 1A. What are the indications for USG in mediastinal tuberculous lymphadenopathy?

At present, USG is of limited utility in the preliminary assessment of mediastinal lymph nodes, for which other cross-sectional modalities like CT or MRI are preferred. However, transmediastinal USG (TMUS) can be used during subsequent follow-up.

Indications for USG in the assessment of mediastinal lymph nodes:

1. Endobronchial USG (EBUS): diagnostic EBUS is performed in conjunction with transbronchial needle aspiration (TBNA) when there are indications to sample the mediastinal lymph node. A complete discussion is beyond the scope of this statement. It is specifically indicated in cases of:

   • Isolated mediastinal lymphadenopathy to establish a tissue diagnosis, especially right and left paratracheal (stations 2R, 2L, 4R, 4L), and subcarinal nodes (station 7).

   • Non- or sub-optimally responsive mediastinal TB to check for drug sensitivity.

2. TMUS: TMUS is a relatively new approach as compared with EBUS. Its effectiveness is highly dependent on the operator's skills due to the anatomical complexity and the limited acoustic window. Therefore, it is currently not recommended as a diagnostic imaging modality for newly suspected cases, where CT or MRI is preferred. However, TMUS may be utilized during subsequent follow-up assessments of mediastinal lymph nodes.[7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

3. Transesophageal endoscopic ultrasound can access the lower mediastinum, including subcarinal (station 7), paraesophageal,[8] and pulmonary ligament regions[9]; it also allows partial access to left paratracheal (4L) and left hilar (10L) lymph nodes.

Remarks

The encouraging results of TMUS in the evaluation of mediastinal lymphadenopathy in the pediatric age group have opened avenues to explore this modality in adults. TMUS can be considered once at baseline (following CT/MRI) and subsequently during follow-up. Current consensus emphasizes the importance of incorporating TMUS as a follow-up imaging tool, particularly in cases with clinical concordance, to optimize resource utilization.[14] [16] [17] [18] [19] [20] [21]

• 1B. What are the follow-up recommendations for TMUS in mediastinal tubercular lymphadenopathy?

According to current recommendations (National Tuberculosis Elimination Program), mediastinal lymph nodes should be followed up with a repeat chest radiograph after 4 months. However, if there is no significant reduction in the size of the lymph nodes, a CT scan is indicated.[3] [22] [23] [24]

Currently, there are no follow-up recommendations for TMUS in mediastinal TB lymphadenopathy. However, we suggest performing a TMUS screening (if feasible) following a CT or MRI at baseline to assess the location, extent, and characteristics of the involved lymph nodes with further follow-up recommendations, summarized in [Table 1].

Table 1 Recommendations for follow-up of mediastinal tubercular lymphadenopathy on TMUS in clinically responsive cases

Timeline (for TMUS)	What to assess
Preliminary (baseline)	● Location  ● Size  ● Internal characteristics of lymph nodes  ● Concomitant pulmonary or pleural involvement
Intensive phase (IP)
Early (2–3 weeks)	Interval improvement in clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of lymphadenopathy
Completion of IP (2 months	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of lymphadenopathy
Completion of continuation phase	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of lymphadenopathy

Abbreviations: CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; TMUS, transmediastinal ultrasound.

Persistent mediastinal lymphadenopathy beyond 4 months after completing anti-TB treatment (ATT) may indicate an alternative etiology, such as sarcoidosis, malignancy, lymphoma, or fungal infection. In such cases, the decision to continue treatment is best guided by correlation with clinical symptomatology. Additionally, a biopsy may be warranted in selected cases to substantiate the findings.[25] [26] [27] [28] [29] [30]

• 1C. What is the technique of TMUS?

The scanning in TMUS begins sequentially from the supraclavicular regions laterally, with a medial sweep reaching up to the sternal notch. Finally, the parasternal regions are evaluated. Traditionally, micro-convex or sector probes are used due to their smaller footprint, which allows for easier probe placement at technically challenging anatomical sites, considering the acoustic limitations posed by the bony rib cage.

However, recent literature on the pediatric population has demonstrated better image quality with linear array transducers (11–18 MHz), owing to the lesser requirement for depth penetration in children. For visualizing deeper lymph nodes (stations 5–7 and 10), an endocavitary probe (3–12 MHz) with a convex footprint may be employed. This probe provides better spatial resolution for superficial structures compared with convex transducers.[19] [20] [21] [22]

Remarks

A summary of transducer selection, probe placement, and anatomical landmarks for various lymph nodal stations is presented in [Table 2]. Despite best efforts, TMUS has limitations in evaluating stations 8 to 14. These stations are assessed using transesophageal ultrasound (stations 8 and 9) and radial EBUS.

Table 2 Technical parameters and surface landmarks in TMUS[19]

Lymph node station	Transducer type (and orientation)	Probe position	Anatomical landmark
1	Linear probe (axial)	Supraclavicular region	Triangle formed by the confluence of IJV, SCV, and BCV
2 3P 4	Linear probe (axial) Endocavitary/micro-convex (axial oblique)	Suprasternal notch	Trachea
3A 4 3A (Medial)	Linear (axial) Linear (longitudinal)	Parasternal	Sternum Trachea Heart and aortic root
3 A 5 6 7 10	Endocavitary Longitudinal (lateral sweep) Endocavitary Steep caudal tilt (lateral sweep)	Suprasternal with caudal tilt	Aortic arch and branches Carina

Abbreviations: BCV, brachiocephalic vein; IJV, internal jugular vein; SCV, subclavian vein; TMUS, transmediastinal ultrasound.

Generally, left-sided mediastinal lymphadenopathy is better evaluated on TMUS compared with the right side, as the predominance of vascular structures on the left provides better acoustic windowing. Several technical limitations may arise during TMUS, such as poor acoustic windows and space constraints for probe placement. These challenges can often be mitigated through technique modifications, such as placing the probe in the intercostal spaces to achieve a more favorable acoustic window or using a transducer with a smaller footprint (e.g., a micro-convex probe) for difficult sites like the suprasternal notch.[19] [20] [21] [22]

Section 2: Pleura

• 2A. What are the indications for ultrasound in TB of pleura?

Transthoracic USG (TUS) plays a significant role in the initial diagnosis and follow-up of pleural TB. While a CT scan is considered the gold standard for detecting pleural abnormalities in TB, USG is a comprehensive one-stop imaging modality, offering the dual benefit of diagnosis and guidance for further procedures such as thoracocentesis.[31] [32] [33] [34] [35] [36] [37]

Indications for USG in Suspected or Proven Pleural TB

1. Diagnosis and quantification of pleural effusion: TUS is the most sensitive imaging modality for detecting pleural effusion, irrespective of the etiology. It can identify as little as 50 mL of effusion.[38] [39]

2. Differentiation of simple and complex effusion: USG is highly effective in distinguishing between simple (anechoic) effusions and complex empyema. Complex effusions are characterized by loculations and septations within the fluid. Additional findings, such as pleural thickening (<1 cm) and pleural nodularity, may also support a tuberculous etiology.[38] [39] [40] [41]

3. Quantification of pleural effusion: several methods of pleural fluid quantification are available, and the practice and preference vary from institution to institution. The commonly used formulae are Goecke's, Eibenberger's, and Balik's. A brief description is given in [Table 3].[42]

4. Image-guided pleural fluid aspiration and pleural biopsy: USG is indispensable for both diagnostic and therapeutic sampling of pleural fluid. It is particularly useful for:

   • – Inserting a percutaneous drain in cases of symptomatic pleural effusion or empyema.

   • – Sampling from localized pleural thickening or loculated empyema.

   • – Guiding biopsy procedures for a thickened pleura.

Table 3 Various methods of pleural fluid quantification

	Patient position	Transducer position	Formula
Goecke	Erect	Longitudinal	EV = X × 90 (X = craniocaudal pleural fluid extent at dorsolateral chest wall in cm)
Goecke	Erect	Longitudinal	EV = (X + LDD) × 70 (X = craniocaudal pleural fluid extent at dorsolateral chest wall in cm LDD = lung base to mid-diaphragm distance in cm)
Eidenberger	Supine	Transverse	EV = 47.6X − 837 (X = maximum perpendicular distance in mm between lung surface and the chest wall at peak inspiration)
Balik	Supine	Transverse	EV = 20X (X = maximum perpendicular distance in mm between lung surface and the chest wall at peak inspiration)

Abbreviation: EV, estimated pleural fluid volume in mL.

With its sensitivity, bedside applicability, and procedural utility, TUS stands out as a crucial tool in the management of pleural TB.[30] [31] [32]

• 2B. What are the follow-up recommendations for TUS in pleural TB?

Symptomatic improvement is noticeable within 2 weeks with resolution of fever. The resorption of pleural fluid is variable and depends on a multitude of factors such as host response, infective burden, and amount. This may take anything from 6 weeks to up to 4 months. Therapeutic thoracocentesis is required in symptomatic pleural effusion. Complex pleural effusion may also require early therapeutic drainage to reduce the infective burden and to prevent any residual pleural thickening.[29] [30] [38] [43] [44] [45] [46] [47] [48] [49] The recommendations for follow-up TUS during treatment are summarized in [Table 4].

Table 4 Recommendations for follow-up of pleural TB with TUS in clinically responsive cases

Timeline (for transthoracic USG)	What to assess
Preliminary (baseline)	Type of pleural involvement: effusion (quantity), thickening, nodularity, complexity, loculations, concomitant pleural involvement Extent of involvement
Intensive phase (IP)
Early (2–3 weeks)	Interval improvement in clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of pleural effusion, complexity, pleural thickening (if increasing), any drainage required
Completion of IP (2 months)	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of pleural effusion, complexity, pleural thickening (if increasing), any drainage required
Completion of continuation phase (CP)	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of pleural effusion, residual pleural thickening

Abbreviations: CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; TB, tuberculosis; TUS, transthoracic ultrasound.

• 2C. What is the technique of TUS in pleural TB?

1. Positioning: the examination is preferably performed in a sitting position with slight forward bending, which facilitates dependent fluid accumulation in the lower hemithorax. Slight manipulation, such as resting, folding, or elevating the arms, helps to widen the posterior intercostal spaces. Supine/decubitus position might be adopted in patients who are unable to sit upright.

2. Probe selection: begin scanning with a low-frequency convex transducer (3–5 MHz) for a generalized overview of the pleural cavity. This is particularly useful for evaluating the extent of voluminous pleural effusion or detecting deep-seated empyema. Follow this with meticulous scanning using a high-frequency linear transducer (5–12 MHz) for a detailed assessment of pleural thickening and nodularity.

3. Scanning technique:

   • Thoracic survey: each hemithorax should be systematically evaluated by dividing it into anterior, lateral, and posterior regions. Each region should be thoroughly assessed cranio-caudally by placing the probe in the intercostal spaces. In cases of interference from acoustic shadowing, the transducer is oriented perpendicular or oblique to the ribs.

   • Landmarks:

   • The pleural line is a bright, echogenic line at the interface of the lung and pleura.

   • The lung sliding sign refers to the respiratory movement of the visceral pleura against the parietal pleura in an aerated lung.

   • Identifying the findings:

   • Pleural effusion: appears anechoic or hypoechoic, depending on its complexity. Internal echoes, septations, and loculations are commonly seen in tuberculous empyema.

   • Pleural thickening: a measurement greater than 3 mm is indicative of a tubercular etiology.

   • Pleural nodularity: hypoechoic or heterogeneous pleural nodules may be present.

   • Subpleural consolidation or atelectasis: these findings may also be observed.

   • Detection of ancillary named signs: these, when present, can add additional diagnostic clue.

     • – Mobile hyperechoic debris in a nonseptated pleural effusion can show “Plankton sign.”

     • – Layering of echogenic contents within pleural fluid in exudative effusion is known as “Hematocrit sign.”

     • – In case of advanced fibrosis, there are multiple fixed, thick septa without any movement.

     • – Pleural effusion with expandable underlying lung shows a sinusoid sign on M mode USG. In case of trapped lung underneath the pleural collection, M mode USG will show absence of sinusoid sign.

This systematic approach enhances the diagnostic utility of TUS in pleural TB.[43] [44]

Section 3: Pericardium

• 3A. What are the indications for ultrasound in TB of pericardium?

USG, in the form of transthoracic echocardiography (TTE), plays a crucial role in both the initial diagnosis and follow-up of tuberculous pericarditis. Its applications can be summarized as follows[50] [51] [52] [53] [54]:

1. Diagnosis:

   • Preliminary assessment: TTE is the primary screening modality in the diagnostic work-up of suspected TB. Its easy availability and rapidity make it the imaging modality of choice for quick evaluation of pericardial effusion, even at the bedside.

   • Characterization of pericardial effusion: TTE differentiates simple effusions from complex ones based on the presence of internal echoes and septations, which are indicative of complex effusions. Complex, exudative effusions are more suggestive of TB, especially in endemic regions.[52] [55] [56] [57] [58] The evaluation of pericardial thickness can also prove additional clue to the etiology. Tubercular pericarditis/effusion is usually associated with more thickening >2 mm. Guided pericardiocentesis can show high ADA levels (≥35 U/L) in pericardial fluid.

   • Detection of complications: TTE is effective in identifying complications such as cardiac tamponade and constrictive pericarditis with imaging features as described in [Table 5].

2. Image-guided interventions:

   • Pericardiocentesis: USG is indispensable for both diagnostic and therapeutic pericardiocentesis.

   • Percutaneous catheter drainage: it facilitates the placement of image-guided drainage catheters for effusion management.

3. Treatment monitoring:

   • Follow-up assessment: USG aids in monitoring the treatment response by evaluating the status of pericardial effusion or identifying any progression to fibrosis ([Table 6]). Signs such as increasing pericardial thickening and the presence of calcifications indicate progression to constrictive pericarditis.

4. Prognostication:

   • During active stages, USG can identify life-threatening tamponade by assessing ventricular filling pressures and diastolic dysfunction.

   • It can also detect features of pericardial constriction, aiding in prognostic evaluations.[28]

Table 5 Sonographic features to differentiate constrictive pericarditis from cardiac tamponade

USG finding	Constrictive pericarditis	Cardiac tamponade
Pericardial effusion	Trivial	Large volume
Pericardial thickening	Present	Usually absent
Chamber collapse Right atrial Right ventricle	Absent Absent	Early systolic collapse (sensitive) Diastolic collapse (specific)
Inferior vena cava	Dilated, may collapse partially	Dilated, noncollapsible
Respiratory variations in mitral/tricuspid inflow	Mild (<25%) variation	Exaggerated (>25%)
Septal motion	Abrupt diastolic bounce	Exaggerated interventricular dependence

Table 6 Recommendations for follow-up of pericardial TB with TTE in clinically responsive cases

Timeline (for TTE)	What to assess
Preliminary (baseline)	At the time of diagnosis, a comprehensive TTE is done to assess the baseline. ● Pericardial effusion (volume, septations, loculations) ● Pericardial thickening (including any calcification) ● Cardiac function and any cues for myocardial involvement
Intensive phase (IP)
Early (2–3 weeks)[a]	Interval improvement in clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.), any signs of heart failure or cardiac tamponade Status of pericardial effusion, complexity, any drainage required
Completion of 1 month of IP	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of pericardial effusion, complexity, pericardial thickening, cardiac function, any drainage required
Completion of 2 months of IP	Status of pericardial effusion or constriction (if any pericardial constriction is identified, cardio-thoracic vascular surgery [CTVS] referral for the relief of constriction).
Continuation phase (CP)	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of pericardial effusion, residual pericardial thickening every 3–6 months for initial 1–2 years, even after completion of ATT.

Abbreviations: ATT, anti-tubercular treatment; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; TB, tuberculosis; TTE, transthoracic echocardiography.

^a An early TTE (1–2 weeks after ATT initiation) may be done in cases with large volume effusion, cardiac tamponade, or following pericardiocentesis.

This comprehensive use of TTE enhances its utility as an essential tool in managing tuberculous pericarditis.[50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60]

• 3B. What are the follow-up recommendations for TTE in pericardial TB?

In pericardial TB, TTE is more frequently warranted than imaging of other sites. This is because USG plays a crucial role, not only in early diagnosis but also in the early detection of complications such as cardiac functional impairment (including cardiac tamponade) and constrictive pericarditis ([Table 5]).

In cases of constrictive pericarditis, ATT is not administered, and such cases are referred to cardio-thoracic vascular surgery for further management.[29] [61] [62] [63] [64] [65] [66] [67]

• 3C. What is the technique of point-of-care ultrasound (POCUS) for the evaluation of pericardial effusion?

POCUS is a technique for quick bedside evaluation of pericardial effusion. The probe is positioned at four predefined stations to assess pericardial effusion rapidly.[67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77]

Patient position: supine. If there is artifactual signal loss from the sternum, reposition the patient to the left lateral decubitus position.

Choice of transducer: phased array.

Placement of Transducer

Pericardial evaluation with POCUS involves one of the four standard cardiac views, similar to those used in TTE.

1. Position A: parasternal view (long/short axis): the probe is placed in the left fourth intercostal space (approximately at the level of the nipple line in males and the inframammary fold in females).

   • For the long-axis view, orient the probe toward the right shoulder.

   • For the short-axis view, rotate the probe 90° to direct it perpendicular to the long axis, aiming toward the left shoulder.

2. Position B: subxiphoid view: the probe is positioned under the xiphoid process and oriented toward the patient's left shoulder. The transducer should be kept as parallel to the skin as possible.

3. Position C: apical view: from the parasternal axial view, slide the transducer down toward the apex of the heart, where the maximum cardiac impulse is felt.[52] [53] [64]

These predefined positions allow for a thorough and quick assessment of pericardial effusion at the bedside.

Section 4: Chest Wall

• 4A. What are the indications for ultrasound in TB of the chest wall?

Role of USG in Chest Wall TB

1. Diagnosis: USG is highly effective in detecting both superficial and deep-seated abscesses. In the chest wall, these abscesses are commonly located along the rib shafts, costochondral junctions, sternal margins, vertebrae, and costovertebral joints. Depending on the extent of caseous necrosis and liquefaction, the internal echogenicity of these abscesses can vary from anechoic to hypoechoic, with the presence of septations and internal echoes. Associated sinus tracts, appearing as tubular hypoechoic structures, may also be present, along with inflammatory changes in the surrounding soft tissues.[67] [68] [69] [70] Bone erosion involving the superficial bones (ribs and sternum) can be well visualized on USG.

2. Characterization: compared with advanced imaging modalities like CT or MRI, USG is more efficient in distinguishing solid from pseudo-solid lesions, such as those seen in complex collections suggestive of pus. This is indicated by the presence of moving internal echoes and the absence of vascularity in complex pus collections that may mimic solid lesions. Additionally, certain internal characteristics, such as debris, septations, and calcific foci, strongly suggest a tubercular etiology.

3. Image-guided interventions: USG-guided sampling (e.g., fine needle aspiration cytology or biopsy) is the recommended method for suspected tuberculous involvement due to the superficial nature of the lesions. Therapeutic drainage may also be performed to alleviate symptoms.

4. Response assessment: USG excels in the follow-up evaluation of cold abscesses, owing to its easy availability, cost-effectiveness, and noninvasive nature. This makes it an excellent tool for monitoring response to treatment and guiding further management.[29] [71] [72] [73] [74] [75]

The consensus highlights the critical role of USG in the management of chest-wall TB, as it supports diagnosis, treatment, and follow-up assessments. Its utility is underscored by its easy accessibility and significant cost advantage compared with other imaging modalities.

This comprehensive approach makes USG a cornerstone in managing chest-wall TB.

• 4B. What are the follow-up recommendations for TUS in chest-wall TB?

There is no standard clinical mandate for the timing of TUS; however, the following suggested timelines for TUS are outlined in [Table 7].[29] [75] [76] [77] [78] [79] [80]

Table 7 Recommendations for follow-up of pleural TB with transthoracic USG in clinically responsive cases

Timeline (for transthoracic USG)	What to assess
Preliminary (baseline)	At the time of diagnosis, a comprehensive TUS is done to assess the baseline  ● Location, size, and nature of the chest wall lesions (abscess, sinus tracts, etc.)  ● Concomitant pleural and peripheral lung involvement (consolidation or collapse) can be evaluated Percutaneous diagnostic sampling and therapeutic drainage (if required) can be done.
Intensive phase (IP)
Early (2–3 weeks or 1 month of IP)[a]	Interval improvement in clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Imaging parameters to assess during follow-up evaluation: ● Size of the lesion: increasing, decreasing, resolved ● Internal characteristic: progressive transition from a hypoechoic to a more complex, organized tissue in responsive cases ● Ancillary findings: resolution of fistula, sinus tracts, if any ● Any new findings (There may be an initial increase in size of the soft tissue lesion due to liquefaction. Hence, this needs to be carefully evaluated in the clinical context).
Completion of IP (2 months)	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of soft tissue lesion, any drainage required
Continuation phase (CP) (3 monthly for 4–6 months or longer and after treatment completion)	Clinical symptomatology (including inflammatory markers such as ESR, CRP, etc.) Status of soft tissue lesion, any drainage required At completion of ATT, follow-up TUS is required to look for resolution of abscess, sinus tracts, or fistula

Abbreviations: ATT, anti-tubercular treatment; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; TB, tuberculosis; TUS, transthoracic ultrasound; USG, ultrasonography.

^a An early transthoracic USG (1–2 weeks after ATT initiation) may be done to evaluate early therapeutic response or need for any therapeutic drainage.

Indication for intervention: if the abscess persists or increases in size during ATT, it may require aspiration or drainage. Diagnostic re-aspiration can be necessary to evaluate drug resistance or to rule out any superimposed infection.

Indications for other investigations: in cases where findings do not resolve or worsen, additional imaging such as CT or MRI may be needed to assess for deeper seated involvement.[29]

• 4C. What is the technique of TUS in chest-wall TB?

• Patient positioning: it is guided by the location of the lesion. In anterior or lateral lesions, the patient is asked to sit upright or semi-recumbent. For a posterior chest-wall lesion, the preferred position is sitting, with slight forward bending, or prone position.

• Transducer selection:

  • – Linear transducer (5–12 MHz): used for detailed assessment of superficial lesions.

  • – Convex transducer (2–5 MHz): used for deep-seated lesions, especially when assessing pleural or lung involvement.

• Placement of transducer: the transducer is placed at the site of swelling or induration. The scanning should cover both the affected area and neighboring sites to assess the extent of involvement. For larger lesions, initial scanning with a convex transducer helps evaluate the deeper extent of the lesion more effectively.[64] [65] [66] [67] [68] [69]

This approach ensures accurate assessment of lesions based on their location and depth, optimizing the use of different transducers for detailed evaluation.

Limitations

Although TUS is an effective imaging tool for quick screening and assessment of the suspected sites, there are several limitations in it being an exclusive imaging modality of choice for the diagnostic evaluation of EPTB.[81] [82] First, this modality is heavily operator-dependent and requires expertise, especially in the evaluation of mediastinal lymph nodes. Second, there are inherent limitations for optimal assessment of USG due to poor acoustic window (due to air-containing lungs and bony rib cage) and anatomical complexity (e.g., intercostal spaces, sternal notch, etc.).[62] [81] Further, it is technically limited in the evaluation of deep-seated lesions for which CT/MRI are superior. Additionally, no single ultrasonographic feature is diagnostic of TB, hence, its role is mainly supportive, which needs further interpretation in the context of clinical and laboratory (microbiology and histopathology) examinations. Hence, USG cannot be taken as a definitive examination during the preliminary assessment of the thorax.[63] [82] Besides, it cannot evaluate concomitant pulmonary parenchymal involvement for which a radiographic modality (chest radiograph and/or CT scan) is mandatory. USG or any other imaging findings lack diagnostic accuracy, in isolation; hence, we recommend the integration of USG with a multidisciplinary approach (e.g., pathology, microbiology) for diagnosing EPTB. This multidisciplinary approach helps in covering a broader diagnostic arsenal by combining the main strengths of USG, viz, accessibility and real-time imaging, thereby improving patient outcomes.[62] [63] [64] [82]

Future Directives

Future directives for TUS in the evaluation of EPTB of the thorax should focus on enhancing its capabilities through technological advancements and standardized protocols. Innovations in ultrasound technology, such as improved resolution and advanced imaging modalities like contrast-enhanced ultrasound, hold promise for better visualization and characterization of TB-related lesions in deep-seated thoracic structures.[65] Additionally, researchers should aim to establish standardized guidelines for TUS in TB diagnosis, ensuring consistency in imaging protocols and interpretation across diverse clinical settings.[66] Integration of artificial intelligence (AI) algorithms for automated image analysis and decision support systems could further augment TUS's diagnostic accuracy and efficiency. These advancements will facilitate TUS's evolution into a more reliable and widely adopted tool for early detection and monitoring of EPTB, thereby improving patient outcomes through timely intervention and treatment.[67]

The unexplored potentialities of TUS should be propounded, especially in resource-constrained endemic regions.[68] Training the radiologists for a meticulous examination of TMUS is a felt need as it requires technical expertise. Human immunodeficiency virus (HIV)-associated TB is another domain where the role of USG needs to be expanded. At present, there are suggestions in place for FASH (focused assessment with sonography in HIV/AIDS) for quick bedside assessment of such patients. The results are especially encouraging for EPTB, which is even more rewarding with laboratory tests as compared with EPTB in the general population.[69]

Further research and clinical awareness are crucial for enhancing the understanding of mediastinal tubercular lymphadenopathy patterns across different age groups. This will aid in the development of more precise diagnostic criteria and therapeutic interventions, ultimately improving patient outcomes for both pediatric and adult populations.[73]

Conclusion

In conclusion, TUS represents a valuable adjunctive tool in the evaluation of EPTB of the thorax, offering real-time imaging capabilities without radiation exposure. While TUS has demonstrated utility in visualizing superficial lesions and guiding procedures, its effectiveness in deep-seated structures remains limited. Continued research efforts aimed at enhancing TUS technology, standardizing imaging protocols, and integrating AI-driven image analysis hold promise for expanding its role in TB diagnosis and management. Collaborative initiatives among clinicians, researchers, and technologists are essential to harness TUS's full potential. This would ensure comprehensive and timely assessment of TB-related thoracic lesions to improve patient outcomes globally.

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