Uncovering the depths of myofascial infection: A clinico-radiological approach

Fascial anatomy: An omnipresent network

From top to toe, birth to death, and at every level from micro to macro, an intricate web of connective tissue – a seamless network that wraps, supports, and connects every muscle, bone, and organ. It is both embryologically and anatomically a single, unified network that envelopes, connects, and supports all body structures. It acts as a hidden adhesive that holds everything together, giving structure and flexibility, while allowing the body to move with grace and ease.^[1]

Relevance of fascia

The fascial structure supports and stabilizes organs and muscles, maintaining their proper positioning and function. Fascial planes segregate muscles into functional compartments, optimizing coordinated movements and biomechanical force distribution. Fascial layers serve as conduits and protective sheaths for neurovascular and lymphatic structures.^[2] The layered organization of muscle and fascial structures is depicted in [Figure 1], demonstrating the anatomical continuum from the skin through the superficial and deep fascia down to the underlying musculature.

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Figure 1:

(a) Illustration of muscle and fascial anatomy: Structural framework of the human body. Image credit: Deep recovery, (b) Schematic cross-section of the thigh illustrating the arrangement of fascial layers. (Adapted from original source: Fasciae of the musculoskeletal system: normal anatomy and MR patterns of involvement in autoimmune diseases and redrawn by the authors).

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Tensegrity, combining tension and integrity, explains how fascia maintains stability throughout continuous tension and discontinuous compression, allowing the body to adapt and respond efficiently without structural damage. The structure and function are intertwined with each movement reflecting their seamless interaction.^[3]

Types of fascia

Classification of Fascia according to depth and location is provided in Flowchart 1.

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Flowchart 1:

Classification of fascia according to depth and location.

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Imaging anatomy of fascia

In healthy individuals, fascia is usually thin and subtle on imaging. Because it is collagen-rich with low water content, it shows low intrinsic signal on MRI and soft-tissue attenuation on CT, making it difficult to visualize directly unless outlined by fat, fluid, or gas. Therefore, fascial anatomy is often appreciated by the boundaries it forms, such as fat planes or displacement caused by pathology. Different imaging modalities each have their strengths and limitations in fascial visualization.

MRI offers superior soft tissue contrast and multiplanar views, excelling in deep fascial evaluation, particularly in the pelvis and intramuscular regions. However, normal fascia appears hypointense on T1- and T2-weighted sequences due to its dense collagen content and low water, often blending with adjacent muscle unless bordered by fat. Fat-suppressed fluid-sensitive sequences tend to obscure fascia because both fat and fascia appear dark. Thus, MRI usually depicts fascia indirectly through fat interfaces or when fluid outlines the planes.

US provides high-resolution, real-time imaging of superficial fascia and some deep fascial layers, benefiting from acoustic contrast between collagenous fascia and adjacent fat or muscle. On US, fascia appears as thin echogenic linear bands at characteristic sites, with multilaminar appearances possible depending on depth and angle, as depicted in [Figure 2]. A major advantage of US is dynamic assessment, as normal fascia glides smoothly over muscles during contraction – an ability unique to this modality which is particularly useful to detect fascial defects and associated herniations. It is particularly useful for assessing limb and facial superficial fascia and is invaluable in guiding procedures, such as nerve blocks targeting fascial planes. Its limitations include restricted penetration and a limited field of view, preventing visualization of deeper or intra-abdominal fascia.

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Figure 2:

Ultrasound appearance of normal fascial layers. Superficial fascia appears as thin echogenic linear bands within the subcutaneous tissue, while deep fascia is seen as a well-defined echogenic layer investing the underlying muscles; a multilaminar appearance may be observed depending on depth and transducer angle.

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CT imaging offers a broad anatomical overview and is often the first-line modality for assessing body compartments. Normal fascia is isoattenuating to muscle and usually only visible when highlighted by surrounding fat, fluid, or gas. In individuals with adequate fat, thin fascial planes may be seen as linear soft-tissue densities separating fat compartments – for example, Gerota’s fascia around the kidneys. However, in lean patients, fascial planes are difficult to discern. CT is particularly useful in detecting gross fascial abnormalities such as thickening, stranding, calcifications, or fluid tracking, and it provides valuable mapping of anatomical compartments in trauma or systemic disease.^[4]

In the head and neck, the fascial system includes the superficial platysma and deeper investing, pretracheal, and prevertebral layers that define spaces like the retropharyngeal and carotid compartments. The superficial musculoaponeurotic system is identifiable on high-frequency US.

Thoracic fascia includes the superficial chest wall fascia, pectoral and clavipectoral fasciae, and the endothoracic fascia lining the pleura. These layers define anatomic planes around the breast and chest wall.^[5]

In the abdomen, fasciae include Camper’s and Scarpa’s layers, transversalis fascia, and the thoracolumbar fascia, which interconnect with vertebrae and abdominal muscles. The renal fasciae (Gerota’s and Zuckerkandl’s) define retroperitoneal compartments. Other key landmarks include the Linea alba and psoas fascia.^[6]

Pelvic fascia comprises parietal and visceral components, including the obturator, piriformis, and pelvic diaphragm fasciae, along with ligamentous condensations such as the uterosacral, cardinal, and pubocervical ligaments in females and Denonvilliers’ fascia in males. The mesorectal fascia serves as a key anatomical landmark in oncologic staging and surgical planning, particularly in rectal cancer.^[7]

In the limbs, superficial fascia houses fat and neurovascular structures, while deep fascia forms intermuscular septa and specialized condensations such as the iliotibial band, palmar aponeurosis, and plantar fascia.^[8]

Despite their subtlety in normal states, fascial planes underpin regional anatomy and serve as essential landmarks across modalities. A comprehensive understanding of fascial anatomy and its imaging characteristics is critical for accurate interpretation and procedural planning. MRI and CT depict fascia indirectly by visualizing adjacent fat and fluid interfaces, whereas US enables direct, dynamic assessment of superficial fascial layers. Recognizing the fascial network’s continuity and regional variations [Flowchart 2] facilitates diagnosis and guides interventions that involve navigating through fascial planes safely and effectively.

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Flowchart 2:

Classification of fascia according to anatomic region.

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Imaging in fasciitis: Modalities, clinical findings, and diagnostic pathways

Fasciitis denotes inflammation (either infectious or non-infectious) of the fascial layers, which serve as connective tissue envelopes surrounding muscles and other structures. The clinical presentations are diverse, ranging from indolent conditions like plantar fasciitis to aggressive, potentially lethal infections such as NF.

NF is the spread of infection along the fascial planes, characterized by rapid progression, extensive soft tissue destruction, high mortality rates, and the urgent need for surgical intervention. Prognosis depends heavily on early detection and prompt, aggressive management, highlighting the critical role of imaging. Clinical differentiation of NF from less severe conditions like cellulitis or abscesses can be challenging, making imaging essential for prompt diagnosis and management.^[9,10] This review examines imaging modalities used in various fasciitis conditions, highlighting their roles, strengths, limitations, and characteristic findings, with a special emphasis on NF but also including eosinophilic, nodular, plantar, palmar, and ischemic fasciitis.

Case 1

An elderly male with a longstanding history of type 2 diabetes mellitus presents with a progressively worsening ulcer over the left ankle. In this case, the ultrasound findings [Figure. 3] confirm the diagnosis of soft-tissue infection with early fasciitis, guiding further management.

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Figure 3:

(a-d) High resolution Ultrasound demonstrates increased echogenicity of the subcutaneous fat (black arrow in a), consistent with oedema. The fat appears disorganized, with thin anechoic fluid strands (red arrow in b) interspersed between lobules. The fascial planes are thickened and indistinct (yellow arrow in c), indicating early fasciitis. No gas foci or well-formed fluid collections are observed- suggestive of early fasciitis. (d) A clinical photograph demonstrates an ulcer over the posterior ankle with areas of black eschar.

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Case 2

A 32-year-old woman, two weeks post-caesarean section, presented with fever, localized swelling, and tenderness over the anterior abdominal wall. A diagnosis of post-surgical anterior abdominal wall abscess with associated fasciitis was considered [Figure. 4].

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Figure 4:

(a-d) Contrast-enhanced computed tomography demonstrated a well-defined fluid collection at the caesarean section site, extending from the subcutaneous tissue into the preperitoneal fat plane (green arrow in d). The collection showed peripheral rim enhancement and surrounding fat stranding, with inflammatory changes tracking along fascial planes (yellow arrow in a) – features consistent with abscess formation (red arrows in b and c) and associated anterior abdominal wall fasciitis.

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Case 3

A middle-aged male with a history of herpes zoster presented with severe pain, erythema, and swelling in the left inguinal region, extending into the thigh and perineal area. MRI [Figure. 5] revealed inflammatory fasciitis, extending along the affected dermatomes.

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Figure 5:

(a-c) Non-contrast MRI revealed diffuse thickening and hyperintensity along the fascial planes on STIR images (red arrows in a to c), consistent with fasciitis secondary to viral infection. bilateral sacroiliac joints are normal

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Case 4

An elderly diabetic female presented with left arm pain and swelling, and sonography of the arm revealed necrotizing fasciitis [Figure. 6]. Ultrasound (US) provides a rapid, cost-effective evaluation with high sensitivity and specificity, offering advantages such as real-time imaging, the ability to assess fascial involvement, and aiding in timely therapeutic decision-making for this life-threatening condition.

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Figure 6:

Transverse sonography of the arm depicting hyperechoic soft-tissue emphysema at the level of the deep fascia with acoustic shadowing (red arrows), suggestive of necrotizing fasciitis.

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Case 5

A 45-year-old female with chronic heel pain and morning stiffness presented for evaluation; MRI of the foot revealed plantar fasciitis [Figure. 7`]. Imaging confirms the diagnosis, rules out alternative pathologies, and guides therapeutic interventions.

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Figure 7:

(a and b) Fat-suppressed T2-weighted magnetic resonance imaging of the foot demonstrates edema within the heel pad, flexor digitorum brevis muscle (yellow arrow in a), and calcaneus (blue arrowhead in a). There is also thickening and increased signal intensity of the plantar fascia at its calcaneal insertion (red circle in a), with adjacent impingement from a calcaneal osteophyte (white arrow in b), consistent with plantar fasciitis.

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Case 6

A 42-year-old man presents with progressive anterior thigh pain and swelling for 3 weeks, associated with difficulty walking. Laboratory evaluation reveals elevated inflammatory markers (ESR, CRP), mild normocytic anaemia, and a positive ANA. Creatine kinase (CK) is mildly elevated [Figure 8].

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Figure 8:

(a-e) Magnetic resonance imaging of the thigh demonstrates diffuse edema (white arrow in b to d) involving the vastus intermedius, vastus lateralis, and rectus femoris muscles, along with deep intermuscular fascial involvement (yellow arrow in a and e), favoring inflammatory myofasciitis.

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Case 7

A 38-year-old female who presents with progressive thigh pain, swelling over the past three weeks, along with difficulty walking and morning stiffness [Figure 9].

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Figure 9:

(a and b) Magnetic resonance imaging of the thigh shows asymmetric involvement with focal areas of high signal intensity tracking along the fascial system, predominantly at the periphery of the muscles near the deep fasciae and fibromuscular planes (yellow arrows in a and b) – suggesting epimysial involvement. The deep peripheral and intermuscular fasciae are thickened and hyperintense, and the superficial fascia (green arrow in a) of the posterolateral aspect of the right leg is also involved, while the underlying muscle signal remains preserved – findings favoring inflammatory fasciitis.

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Case 8

A 30-year-old female presents with localized pain and swelling over the anteromedial aspect of the left leg following minor blunt trauma. Clinical examination revealed tenderness and erythema in the region. No open wounds or systemic signs of infection were reported [Figure 10].

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Figure 10:

(a-e) Magnetic resonance imaging of leg shows focal T1/T2/PDFS hyperintensities in the subcutaneous fat and fascia at the anteromedial mid-third of the left leg are consistent with cellulitis and post-traumatic fasciitis, characterized by linear fascial edema (yellow arrows in a-e) without abscess, myositis, osteomyelitis, fracture, or neurovascular involvement – features that favor a superficial, early inflammatory process and help distinguish it from deeper or necrotizing soft tissue infections. (f) External bruise depicted in a clinical photograph.

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Case 9

A 30-year-old female with leg pain and swelling was found to have isolated soleal vein thrombosis with secondary fasciitis and myositis on MRI and Doppler, reflecting venous stasis–induced inflammation without abscess or osteomyelitis [Figure 11].

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Figure 11:

(a-d) Magnetic resonance imaging of the leg (PDFS) reveals acute thrombosis of the soleal vein (red arrow c and d) with secondary myositis involving multiple muscle groups and fasciitis (yellow arrow in a, b and d) across anterior, medial, and lateral compartments, associated with mild subcutaneous edema and no evidence of abscess, necrosis, or osteomyelitis.

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Case 10

A 7-year-old boy presents with fever, right leg pain, and progressive swelling over 2 weeks. There is trans-fascial spread of infection with associated deep fasciitis, indicating aggressive soft tissue involvement [Figure 12].

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Figure 12:

(a-h) coronal and (b) sagittal computed tomography (CT) and (e and f) sagittal magnetic resonance imaging (MRI) show that an abnormal marrow signal is noted in the distal tibial diaphysis and epiphysis, with cortical irregularity and a focal sequestrum (red arrows). (a-d) Axial CT shows mixed lytic and sclerotic changes with cortical breach (red arrows in a-d), consistent with acute-on-chronic osteomyelitis, while (e-h) axial MRI demonstrates surrounding soft tissue hyperintensity on T2/short tau inversion recovery (STIR) with thickening and edema along intermuscular and subcutaneous fascial planes (yellow arrows in g and h), indicating fascial spread of infection without a well-formed abscess. (a-h) Abnormal marrow signal involving the distal tibial diaphysis and epiphysis with cortical irregularity and a focal sequestrum (red arrows in a to f); (a-d) CT demonstrates mixed lytic and sclerotic changes (red arrows in a to d) along with cortical breach, consistent with acute-on-chronic osteomyelitis. (e-h) MRI of the leg reveals surrounding soft tissues show ill-defined hyperintensity on T2/(STIR) with thickening and edema along the intermuscular and subcutaneous fascial planes (yellow arrows in g and h), suggestive of fascial spread of infection. No well-formed abscess is seen.

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Case 11

A 48-year-old male presents with fever, painful scrotal swelling, and perineal discomfort [Figure 13].

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Figure 13:

(a-e) Magnetic resonance imaging (PDFS) demonstrates widespread inflammation affecting the scrotum, perineum, and perianal regions, with a complex loculated scrotal collection containing fluid-fluid levels and gas (red arrows b, d and e), tracking through the inguinal canal into the lower anterior abdominal wall, retroperitoneal, and preperitoneal compartments. The inflammation spreads seamlessly along fascial planes (yellow arrows a to c) without overlying dermal disruption, consistent with deep soft tissue infection.

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Imaging modalities

Accurate imaging assessment of fasciitis is essential for early diagnosis, treatment planning, and differentiation between non-necrotizing and necrotizing forms. A multimodality approach [Table 1] is often required, depending on clinical presentation, resource availability, and patient stability.

US provides a rapid, bedside assessment and is particularly useful in early or superficial fasciitis. It offers high sensitivity (~85.4%) and specificity (~ ranged from 44.7% to 98.2%), especially for detecting fascial thickening, hypoechoic fluid collections (>4 mm in thickness) along fascial planes, cobblestone-pattern subcutaneous edema, and subcutaneous gas as echogenic foci with dirty shadowing. Interpretative accuracy may vary depending on the operator’s expertise and the patient’s body habitus, potentially impacting diagnostic reliability [Figure 3].^[11] Conventional radiography remains the most readily available and is often employed as the initial imaging modality in clinical evaluation. While radiographs have limited sensitivity (~49%) in early fasciitis, imaging may reveal soft tissue thickening with loss of normal fascial plane definition.

The detection of soft-tissue gas – though infrequent – is a highly specific finding (~94%) and suggests advanced or necrotizing infection. Early-stage disease often shows normal findings on radiographs, limiting their diagnostic utility.

CT is frequently utilized in acute settings due to its rapid acquisition, wide availability, and excellent spatial resolution. It demonstrates high sensitivity (80–93%) for detecting NF and plays a key role in early diagnosis and surgical planning. The CT findings include fascial thickening, fluid tracking along fascial planes, non-enhancing soft tissue suggestive of necrosis, and the presence of gas within deep soft tissues – a hallmark of necrotizing infection.^[12] A sectional schematic of the thigh is presented that highlights the progressive imaging features of NF, demonstrating the involvement of various fascial and soft tissue compartments at different stages of the disease [Figure 14].

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Figure 14:

Cross-sectional schematic of the thigh illustrating key features of necrotizing fasciitis: (i) subcutaneous and subfascial emphysema, a hallmark of the disease, (II) diffuse thickening of the superficial fascia seen in initial stages, (III) subfascial fluid accumulation along the superficial fascial layers, indicative of early infection, and (IV) fluid tracking along deep and intermuscular fascial planes, characteristic of advanced disease.

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While the specificity is moderate, CT effectively delineates the anatomical extent of disease, guiding surgical debridement and monitoring disease progression, especially when MRI is contraindicated or unavailable. CT remains the most sensitive modality for detecting soft tissue gas, a hallmark finding virtually pathognomonic for NF [Figure 4].

MRI is the gold standard for assessing fasciitis, providing detailed soft tissue contrast and comprehensive multiplanar imaging for accurate evaluation. MRI reliably demonstrates fascial thickening, fluid tracking, contrast enhancement, and adjacent muscle involvement, with sensitivity up to 93%.^[13] MRI allows for early detection of inflammatory changes and tissue necrosis before overt clinical decline. Limitations include longer scan time, limited availability, contraindications (e.g., pacemakers), and reduced feasibility in unstable patients.

Fasciitis secondary to herpes zoster is an uncommon presentation, reflecting an unusual form of viral involvement of soft tissues [Figure 5]. A case report by Can and Gözel describes a 59-year-old diabetic female who developed NF following a herpes zoster infection. These findings highlight the critical need for prompt identification and timely management in atypical clinical scenarios. This case illustrates the importance of maintaining a high index of suspicion for uncommon presentations of herpes zoster, especially in immunocompromised patients.^[14]

Types of fasciitis and their Imaging features

Types of Fasciitis and their Imaging features are listed in Flowchart 3.

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Flowchart 3:

Types of fasciitis.

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1. Necrotizing fasciitis

2. Eosinophilic fasciitis (EF)

3. Nodular fasciitis

4. Plantar fasciitis

5. Palmar fasciitis

6. Atypical decubital fibroplasia (ischemic fasciitis).

Ischemic fasciitis (atypical decubital fibroplasia)

Ischemic fasciitis is a pseudo-sarcomatous lesion seen in elderly or immobilized patients, typically arising from repetitive pressure-induced ischemia over bony prominences.^[24]

Autoimmune fasciitis on MRI reveals inflammation that closely follows the intricate fascial architecture of the musculoskeletal system.^[25,26]

MRI is essential in idiopathic inflammatory myopathies for detecting muscle edema and fasciitis, aiding in early diagnosis, targeted biopsy, and monitoring therapeutic response.^[27] The MRI appearance [Figure 8] of fascial involvement in autoimmune disorders mirrors the intricate fascial architecture of the musculoskeletal system.

In this context, we present another similar case in which MRI [Figure 9] of the thigh reveals fascial thickening and hyperintensity with signal tracking along deep and superficial planes.

Post-traumatic soft tissue inflammation can present with overlapping clinical features of infection, making imaging crucial for accurate localization and characterization.^[28]

In this case, MRI was performed to evaluate the extent of soft tissue involvement and to differentiate between cellulitis, fasciitis, and deeper infectious or structural pathologies following minor blunt trauma [Figure 10].

In patients with non-specific lower limb symptoms such as pain, swelling, or MRI findings of fasciitis and myositis without an obvious cause, vascular etiologies are often overlooked.^[29]

MRI reveals acute thrombosis of the soleal vein with secondary myositis involving multiple muscle groups and fasciitis across anterior, medial, and lateral compartments, associated with mild subcutaneous edema and no evidence of abscess, necrosis, or osteomyelitis [Figure 11].

The importance of considering distal venous thrombosis, such as plantar vein thrombosis, is underscored as a potential cause of secondary fascial and muscular inflammation in patients presenting with unexplained leg pain, myositis, or fasciitis on MRI.^[30]

Fascial planes act as essential anatomical scaffolds that organize soft tissues, akin to a busy highway network spread throughout the musculoskeletal system of the body. However, this can act as a double-edged sword, and the intricate fascial network may become a potential pathway for rapid and extensive spread of infection/inflammation.

Loss of their barrier function permits pathogens to traverse uninhibited across compartments. Thus, fascia may be aptly described as “the fast lane to multicompartmental spread.”

We present two cases of osteomyelitis [Figures 12 and 13] in which the fascial planes are vividly outlined by inflammatory changes on MRI, underscoring their role as key conduits for rapid and extensive spread of infection.^[31]

Imaging in staging and treatment monitoring

Imaging is crucial beyond diagnosis, playing a vital role in assessing disease extent, particularly in NF. CT and MRI effectively map anatomical involvement, guiding surgical decisions on debridement extent. Post-operative imaging helps identify residual disease or complications, guiding further therapeutic decisions.

Emerging techniques

Advanced techniques such as diffusion-weighted MRI^[32] and elastography show promise in diagnosing the disease early, differentiating inflammatory fluid from necrosis, and quantifying fascial stiffness, respectively. These methods may further enhance the diagnostic accuracy and clinical management of various fasciitis types.^[33]

The systematic diagnostic algorithm for fascial disorders is mentioned in Flowchart 4. Imaging features in fasciitis are given in Table 2.

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Flowchart 4:

Systematic diagnostic algorithm for fascial disorders.

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