Basics of msk ultrasound By Dr. Raham Bacha

ال بحانك ُس� لنا قالو ِع�لَم العليَم� انت انك ِعل�متنا ما ا�ال�

الحكيَمSurah Al Baqarah verse 32

By: Dr. Raham BachaMD, MSc Sonology.Lecturer of Ultrasound (UIRSMIT)

The university of

Lahore

Basics of MSK Ultrasound

• “ULTRASOUND IMAGING IS NOT A PASSIVE PUSH-BUTTON ACTIVITY; RATHER IT IS AN

INTERACTIVE PROCESS INVOLVING A SKILLED CLINICIAN, PATIENT,

TRANSDUCER, INSTRUMENT, AND EXPERIENCED INTERPRETER.

UNDERSTANDING THE PHYSICAL PRINCIPLES INVOLVED CONTRIBUTES TO

THE QUALITY OF MEDICAL CARE INVOLVING DIAGNOSTIC SONOGRAPHY”

{ULTRASOUND SEES THE FIRE – AS WELL AS THE SMOKE}

By; Dr. Raham Bacha

By; Dr. Raham Bacha

By; Dr. Raham Bacha

By; Dr. Raham Bacha

MSK US appearing on the horizon, is the more frequent application of diagnostic ultrasound to image musculoskeletal structures and the extremities of the body.

Sonography’s unique real-time capability, which permits examination during movement, and allows guidance of biopsy needles, combined with the exquisite resolution of state-of-the-art scanners and high-frequency transducers, makes musculoskeletal sonography a powerful tool for diagnosing abnormalities of the soft tissues.

EQUIPMENT SELECTIONMusculoskeletal structures are long, striated and many times layered tissues. Due to the striated morphology of these tissues and their superficial location, high frequency, linear array transducers are best suited for this application. It is recommended that no less than 7.5 MHz transducers be used for musculoskeletal examinations of the extremities. Ideally, 8.0 MHz and above provide the highest resolution.

PROBE PLACEMENT

It is very important to maintain accurate transducers placement in musculoskeletal sonography. Due to the close proximity of several distinct structures in a small area, a slight displacement of the probe can produce inaccurate images. If the image states it is a “midline” image be sure to be as close to midline as possible.

IMAGE ORIENTATION

Regardless of right or left

Longitudinal views: left side of the image is CEPHALAD.

Transverse views: left side of the image is the PATIENT’S

RIGHT

3 STEPS TO SUCCESSFUL IMAGING

1. Image GENERATIONPatient & probe position, grayscale settings

2. Image RECOGNITIONIdentify Individual Interfaces from the bony cortex UP to the skin surface!

3. Image INTERPRETATIONDetermine abnormal findings by knowing normal!

BASIC NORMAL MUSCULOSKELETAL ULTRASOUND ANATOMY

Skeletal MuscleOn longitudinal views, the muscle septae appear as echogenic structures, and are seen as thin bright linear bands. On transverse views, the muscle bundles appear as speckled echoes with short, curvilinear bright lines dispersed throughout the hypoechoic background.

Subcutaneous TissueSubcutaneous tissue is isoechoic with skeletal muscle. The difference between subcutaneous tissue and skeletal muscle visualized on ultrasound is the septa do not lay in lines or layers. More conspicuously; a thick, continuous, hyperechoic band usually separates subcutaneous fat from muscle.

Cortical BoneOn ultrasound examination, normal cortical bone appears as a continuous echogenic (bright) line with posterior acoustic shadowing (black).

FasciaFascia is a collagenous structure that usually surrounds the musculotendinous areas of the extremities. The fascia is then encompassed by subcutaneous tissue. Many times, the fascia is seen inserting onto bone, and blending with the periosteum. Normal fascia appears as a fibrous, bright/hyperechoic structure

PeriosteumOccasionally, a thin echogenic line running parallel with the cortical bone is demonstrated on ultrasound, this is likely the periosteum. However, in normal situations, the periosteum is not visualized by ultrasound. Injuries to the bone, especially those damaging the cortex, periosseous soft tissues, and periosteum will produce a periosteal reaction, which is visible

TendonsA normal tendon on ultrasound examination is a bright/echogenic linear band that can vary in thickness according to its location. The internal echoes are described characteristically as having a fibrillar echotexture on longitudinal views. On ultrasound the parallel series of collagen fibers are hyperechoic, separated by hypoechoic surrounding connective tissue. The fibers will be continuous and intact. Interruptions in tendon fibers are visualized as anechoic areas within the tendon. Tendons are known to be anisotropic structures.

LigamentsOn ultrasound examination, a normal ligament is also a bright echogenic linear structure. However ligaments have a more compact fibrillar echotexture. Individual strands / fibers of the ligaments are more closely aligned. Ligaments are composed of dense connective tissue, like tendons, but there is much variability in the amounts of collagen, elastin and fibrocartilage within a ligament, which makes its ultrasound appearance more variable than tendons.

BursaeIn a normal joint, the bursa is a thin black/ anechoic line no more than 2 mm thick. The bursa fills with fluid due to irritation or infection. Depending on the extent of effusion, the bursa will distend and enlarge; internal brightness echoes are inflammatory debris.

Peripheral NervesHigh-frequency transducers allow the visualization of peripheral nerves that pass close to the skin surface. Peripheral nerves appear as parallel hyperechoic lines with hypoechoic separations between them. On longitudinal views, their appearance is similar to tendons, but less echogenic. On transverse views, the peripheral nerves’ individual fibers, and fibrous matrix, present with multiple, punctate echogenicities (bright dots) within an ovoid, well-defined nerve sheath.

ANISOTROPYAn / iso / tropy.To not have equal properties /characteristics/ appearances on all axes. The property of being directionally dependent. Produced when the probe is not perpendicular with the structure being evaluated. Most common artifact in musculoskeletal ultrasound.

Current, developing and potential indications for MSUS

EFFUSIONProven indication: Diagnosis of joint, tendon sheath and bursal effusion. Aspiration of effusion. Differentiation of cystic from solid masses, detection of cyst rupture, sinus and fistula. Diagnosis of vascular and nerve compression syndromes by fluid collections

Developing Indication:Role of MSUS in improving efficacy of joint and bursal injection

Potential Indication:Differentiation of type of effusion: US microscopy of synovial Fluid

SYNOVIUMProven indication: Diagnosis of synovial proliferation and synovitis

Developing Indication:Diagnosis of lesser degrees of synovitis. Differentiate active from inactive synovitis

Potential Indication:US used as standardized outcome measure for synovitis in RA trials. US used to classify joint involvement (oligoarticular, polyarticular). Development of tissue specific and immunospecific contrast agents. US synovectomy (high-intensity focused US)

BURSA

Proven indication: Diagnosis of superficial and deep bursitis. Bursal aspiration and injection

Developing Indication:Differential diagnosis of true effusive bursitis from soft tissue inflammation (greater trochanter bursitis vs. greater trochanter enthesitis without effusion)

Potential Indication:Improve understanding of bursal function and pathology

BONE

Proven indication: Demonstration of joint erosion

Developing Indication:Diagnosis of fractures, bone tumors, periosteal disease

Potential Indication:US erosion included in diagnostic criteriafor RA.US erosion used as standardizedoutcome measure in RA trials.Differentiate active vascularized erosionfrom inactive erosion

TENDON/LIGAMENTProven indication: Diagnosis of tendon damage, rupture, tendonitis or tenosynovitis. Diagnosis of ligament injury or enthesitis. Improve assessment of indication for surgery

Developing Indication:Monitoring of response to therapy, surgery. Role of MSUS in improving efficacy of tendon sheath and soft tissue injection

Potential Indication:Differentiate active from inactiveenthesitis. Quantitative score of peripheralenthesitis. Improve understanding ofpathogenesis of mechanical andinflammatory enthesitis

SKINProven indication: Measure skin thickness in scleroderma. Detect subcutaneous oedema. Detect subcutaneous hypertrophy and atrophy, abscess, calcification, foreign body, nodule or tumors

Developing Indication:Application of skin thickness as a standard measure of outcome in, scleroderma. Objective monitoring of oedema after therapy. Monitoring of subcutaneous hypertrophy and atrophy, abscess, calcification, foreign body, nodule or tumor

Potential Indication:Diagnosis of scleroderma. Differentialdiagnosis of cellulitis, necrotizing fasciitis,subcutaneous pathology

CARTILAGE

Proven indication: Imaging of local and generalized cartilage defects and calcification

Developing Indication:Monitoring of cartilage thickness homogeneity cartilage disease

Potential Indication:Diagnosis of osteoarthritis and othercartilage disease

VASCULATURE

Proven indication: Detection of inflammation with power Doppler. Imaging of location and morphology of vascular structures

Developing Indication:Objective and reproducible quantification of inflammation with power Doppler. Correlation of MSUS with histological diagnosis of temporal arteritis and vasculitis

Potential Indication:Imaging of ‘normal ’blood flow in joints. Diagnosis of temporal arteritis without recourse to biopsy. Diagnosis of medium and large vessel vasculitis. Diagnosis and monitoring of Raynaud ’s disease

SALIVARY GLANDS

Proven indication: Demonstration of salivary gland size and morphology

Developing Indication:Correlation of MSUS findings with labial gland histology

Potential Indication:Diagnosis of Sjogren’s syndrome

INDICATIONS FOR MSK ULTRASOUND IN EMERGENCY DEPARTMENT

Clinical Suspicion for:Fracture Joint Dislocation Joint Effusion Tendon Tear/Laceration Ligament Injury

Procedure Guidance for:Fracture and Joint Relocation Arthrocentesis Fracture Hematoma Block

• Wrist • Mass Tenosynovitis • Tendon rupture • Joint synovitis Pulley

rupture • Sagittal band injury • Central slip injury • Trigger finger • Pulley ganglion • Rugby/jersey finger • Foreign body

• FCU/FCR • ECU• UCL • Hammer hand• Ganglion • De Quervains Knee• FCR• CTS• Guyons canal• Wartenbergs syndrome

• Elbow• Lateral epicondylitis • Medial epicondylitis • Radial nerve

compression • Median nerve

entrapment, pronator syndrome

• Triceps tendon injury • Snapping triceps

syndrome

• Ulnar nerve neuropathy • Ulnar nerve

subluxation • Olecranon bursitis • Synovitis • Septic arthritis /

effusion

• Shoulder• Bursitis • Full thickness cuff

tears • Calcific tendonitis• LHB: rupture• LHB: dislocation• Septic arthritis• Rotator cuff tears

• • Subdeltoid-subacromial bursitis (SD- SA)

• • Biceps tendonitis/tenosynovitis

• • Gleno-humeral effusion

• Ankle/Foot• Tendinopathy• Tears• Sheath effusions• Peroneal dislocation• Calcific tendinitis• Retrocalcaneal bursitis• Postoperative tendon

tear• ATF ligament

• CF ligament• Ant tibiofibular ligament• Joint effusions• Synovitis• Nerve entrapment• Plantar fasciitis• Retinacula• Ganglion cysts

• Knee• Patellar

tendinopathy/tear• Quadriceps

tendinosis/tear• Pes anserinus

tendinobursitis• Baker´s cyst

• Periarticular bursitis• Periarticular

ganglion• Synovitis, effusion• Septic arthritis• Nerve pathology• Osgood-Schlatter,

SindingLarsen

• Hip• Fluid detection• Extra-articular

snapping hip• Synovitis/effusion/

synovial cysts• Sports hernias• Morel-Lavallee

lesions

• High-grade muscle injuries

• Lateral femoral cutaneous nerve

• Femoral nerve

Muscles and

Tendons Anatomy

TENDONS

• Critical biomechanical units in the musculoskeletal system• transmit the muscular tension to mobile skeletal segments• extremely resistant to traction• extremely variable shape and dimensions, characterized

by the presence of dense fibrous tissue arranged in parallel bundles

• consist of about 70% of type I collagen fibers• fibrocytes endowed with large laminar protrusions, named

tenocytes or alar cells Among the primary bundles• elastic fibers (about 4%) can also be found; acts as

“shock absorber”

TENDONS

• The primary bundles are assembled to form secondary bundles which are clustered in tertiary bundles surrounded by The endotenon

• the whole tendon is surrounded by epindotenon.

• Tendon may either be • Supporting

or • Sliding tendon.

Anchor or supporting tendons (such as the Achilles and the patellar tendon) are typically bigger and stronger than sliding tendons, they are not provided with a synovial sheath, but they are surrounded by a connective lamina external to the epitenon, called peritenon; the two connective sheaths (epitenon and peritenon) form the paratenon together with highly vascularized adipose and areolar tissue

Sliding tendons are;• wrapped in a covering sheath (tenosynovial sheath)

whose function is to guarantee better sliding and protection to the tendons when they run adjacent to irregular osseous surfaces, sites of potential friction. The teno-synovial sheath consists of two layers:

• Visceral layer, strictly contiguous to the epitenon, and

• Parietal, more external, layer; the two layers come together to form

• a synovial “fold” named mesotenon. A closed cavity, containing a very small amount of synovial fluid

Tendons may present with less vascularized zones, named critical areas, which are extremely important in the pathogenesis of several tendon diseases. Examples include the pre-insertional area of the supraspinatus tendon of the shoulder, or the central part of the Achilles tendon, which typically constitute highly susceptible sites of degenerative disease and tendon rupture.

The point of union between the tendons and the muscle is called myotendinous junction and that of bone and tendon is named as osteotendinous junction (enthesis). At The level myotendinous junctionis usually the tendon fibers are intertwined with the myofibers.

In contrast The osteotendinous junction has a more complicated structure: its nature may be either fibrous or fibrocartilaginous according to the tendon mobility, the angle formed between the tendon fibers and the bone, and the presence of an underlying retinaculum. The tendons moving in a single spatial plan and whose insertion on the bone occurs with an acute angle (for example, the flexor tendons of the toes), have a fibrous enthesis. The same situation occurs for tendons whose course is modified and kept in position by a retinaculum – for example the peroneal tendons – and whose insertion on the bone once again forms an acute angle.

Retinaculum is a transversal thickening of the deep fascia attached to a bone’s eminence. The biomechanical function of a retinaculum is to keep the tendons in position as they pass underneath it, in order to avoid their dislocation during muscular action. Retinacula therefore guarantee that tendons are correctly deviated and kept in position in their respective osteofibrous canals.Retinacula are typically found in the wrist and ankle

• Some of the important retinaculum are;

• The transverse carpal ligament• the ankle retinacula• flexor annular pulleys

Ligaments are analogous structures to that of tendons; however, they are thinner and they contain a higher amount of elastin, which is a necessary element to supply these structures with some degree of elasticity for their very important biomechanical role in the stabilization of joints.

There are two types of ligaments: • The intrinsic capsular ligaments, which

appear as localized thickenings within the capsule with a strengthening function, and

• The extrinsic ligaments, which are independent from the fibrous capsule and can be further classified as;

• Extra-capsular and

• Intra-capsular ligaments

Appearance of Tendon, Retinaculum

and Ligament

On Ultrasound

TENDONNowadays US represents the gold standard technique for the assessment of tendons.

With the advent, for clinical purposes, of high resolution transducers and specific image processing software, it became possible to make detailed analysis of the shape and structure of tendons. In addition, US is the only technique that allows the sonologist to perform a dynamic study of tendons, which is extremely important for the diagnosis of tendon pathology. In longitudinal ultrasound views (long axis), the tendons appear as echoic ribbon-like bands, defined by a marginal hyperechoic line corresponding to the paratenon and characterized by a fibrillar internal structure. The fibrillar echotexture is represented by a succession of thin hyperechoic parallel bands, slightly wavy, which tend to grow apart from one another when the tendon is released and to move closer when the tendon is tense.

DISEASED STATENormally there is a slight difference between sliding and anchor tendons. There is a small amount of synovial fluid around the sliding tendons and can be appreciated by meticulous examination.

An increase in the amount of fluid in the mesotenon around the tendon can be examined in tenosynovitis.

Supporting tendon:On the other hand, anchor tendons are surrounded by the peritenon, a layer of dense connective tissue leaning on the epitenon, which contributes to constitute the paratenon. The paratenon appears as an echogenic line surrounding the tendon, without the possibility of distinguishing, in normal conditions, between peritenon and epitenon

The gray-scale ultrasound technique is still not able to recognize indirect signs of inflammation.By implementing Power Doppler techniques with the information obtained from grayscale image make the examiner able to identify the hemodynamic state of the tendon.Normally the tendon have low metabolic activity and the blood supply is given by highresistance arteries and small veins, too thin to bestudied with the Doppler technique.

Several conditions such as inflammatory, posttraumatic and infectious, are responsible for the activation of vascular hyperemia with an increase in blood flow and a drop in vascular resistance

RETINACULA

Appear on ultrasound as thin hyperechoic structures located more superficially than the sliding tendons, in very critical areas from a biomechanical point of viewDynamic Scanning and high amount of gel is used as a spacer in order to avoid any pressure on the tissue, for the evaluation of retinacula.

Transverse US scan of the medial compartment of the ankle

LIGAMENTS

The structure of ligamentsis very similar to that of tendons; the main differences are reduced thickness and a less regular arrangement of structural elements; for this reason, it is harder to study ligaments with US than tendons.

The US examination of ligaments, unlike tendons, is mainly performed using long axis views, the transducer being aligned on the ligament’s major axis. Transverse views (short axis) have poor diagnostic value. With US, ligaments appear as homogeneous, hyperechoic bands, 2-3 mm thick, lying close to the bone

• The most common ligaments to assess with US are;

• Ligaments of the medial and lateral compartments of the ankle (deltoid, anterior talofibular and fibulocalcaneal)

• The collateral ligaments of the knee, • The collateral and annular ligaments of the

elbow, • The coraco-acromial and coraco-humeral

ligaments of the shoulder and the ulnar collateral ligament of the thumb

Transverse US scan of the lateral compartment of the ankle.The anterior talo-fibular ligament (*) is tight between the anterior part of the lateral malleolus (P) and the talus (A)

Longitudinal US scan of flexor digitorum tendons at themetacarpophalangeal joint.The first (A1) out of five pulleys isclearly shown over the tendons.FP= flexor digitorum profundus;FS= flexor digitorum superficialis;PH= proximal phalanx;H= metacarpal head;P= palmar plate;C= cartilage

• The MCL is a flattened, large structure extending from the medial femoral condyle to the medial condyle of the tibia

• it is about 9 cm long and it is divided into two components, deep and superficial, which are separated by a thin layer of loose connective tissue. The deep component is then divided into

• menisco-femoral ligament• menisco-tibial ligament.

• Sonographically the MCL appears as a• trilaminar structure consisting of two

hyperechoic layers, separated by a central interleaved hypoechoic area. The hyperechoic bands correspond to deep and superficial fiber bundles; whereas the loose areolar tissue constitutes the hypoechoic central area that divides the superficial component from the deep one

Longitudinal US scan of the medial compartment of the knee. Thecomplex structure of medial collateral ligament is shown.* = superficial portion,MF= meniscofemoral deep portion,MT= menisco-tibial deep portion;C=femoral condyle;T= tibial plateau;M= meniscus

MUSCLESMuscle is made of bundles of contractile striated muscle fibers with theirmajor axis lying along the contraction direction. The fibers have a cylindrical or polyhedral shape. These muscle fibers have a considerable length, varying from a few millimeters to several centimeters, and a width between 10 and 100 mm.

Muscular fibers are arranged parallel to one another and they are supported by a matrix of connective tissue. Muscle is externally surrounded by a thick connective sheath called the epimysium; from the internal aspect of this sheath several septa invigilate to form the perimysium, which surrounds diverse bundles of muscular fibers, named fascicles (bundle of fibers) (گھچا).

Muscular fibers are arranged parallel to one another and they are supported by a matrix of connective tissue. Muscle is externally surrounded by a thick connective tissue sheath called the epimysium; from the internal aspect of this sheath several septa invigilate to form the perimysium, which surrounds diverse bundles of muscular fibers, named fascicles (bundle of fibers) (گھچا).Very light and thin septa arising from the perymysium spread into the fascicles to surround every single muscular fiber and thus form the endomysium.

The epimysial, perimysial and endomysial coverings come together where muscles connect to adjacent structures like a tendon, periosteum, aponeurosis or the dermis.at the endpoints of the muscular fiber, the myofibrils are attached to the sarcolemma. By means of these devices, the muscular fibers are strongly connected to the terminal insertion.

The internal structure of muscles can be easily assessed by ultrasound imaging. The epimysium appears hyperechoic external band measuring a maximum of 2-3 mm of thickness and, on longitudinal US sections, continues without interruption along the corresponding tendon profile. The perimysia are seen as hyperechoic lines separating the contiguous hypoechoic muscular fascicles from one another

The typical pennate structure of muscles canbe easily assessed in longitudinal axis views where the hyperechoic fibro-adipose septaconverge, with a mainly parallel course, on a central aponeurosis, appearing as a thin, highly reflective bandpennation angle; is the angle measured between the muscular fibers direction and the central aponeurosis axis

NERVESFrom an anatomical point of view, nerves are characterized by a complex internal structure made of nervous fibers (containing axons, myelin sheaths and Schwann cells) grouped to form fascicles, and loose connective tissue (containing elastic fibers and vessels)

Nerves are externally surrounded by a sheath called the epineurium; several septa invigilate from it to form the perineurium, which surrounds bundles of neurve fibers, named fascicles (bundle of fibers) (گھچا).Very light and thin septa arising from the peryneurium spread into the fascicles to surround every single neurve fiber and thus form the endoneurium. The connective tissue intervening between the outer nerve sheath and the fascicles is commonly referred to as the interfascicular epineuriumand houses the nerve vasculature.

With the current generation of high-fequency“small parts” transducers and compound technology, US has become a well-accepted and widespread imaging modality for evaluation of peripheral nerves. The improved performance of these transducers has made it possible to recognize subtleanatomical details with US at least equal to or even better than surface-coil magnetic resonance (MR) imaging for the assessment of wide range of pathological conditions affecting nerves

Apart from the availability of high resolution transcucers, nerve US requires indepth knowledge of anatomy and close correlation of imaging findings with the patient’s clinical history and the results of electrophysiological studies.

With these credentials, US provides low-cost and non-invasive imaging, speed of performance, and other important advantages over MR imaging, including a higher spatial resolution and the ability to explore long segments of nerve trunks in a single study and to examine nerves in both static and dynamic states with real time scanning.

On long axis planes, nerves typically assume an elongated appearance with multiple hypoechoic parallel linear areas, which correspond to the neuronal fascicles that run longitudinally within the nerve, separated by hyperechoic bands. On short axis planes, high-resolution US demonstrates nerves as honeycomb-like structures. Hypoechoic fascicles embedded in a hyperechoic interfascicular epineurium.

The number of fascicles in a nerve may varydepending on the occurrence of nerve branching. In nerve bifurcations, the nerve trunk divides into two or more secondary nerve bundles, whereas each fascicle enters only one of the divisional branches without splitting. The outer boundaries of nerves are usually undefined due to the similar hyperechoic appearance of both the superficial epineurium and the surrounding fat.

Generally speaking, nerves are compressible structures and alter their shape depending on the volume of the anatomical spaces within which they run, as well as on the bulk and conformation of the perineural structures. Across synovial joints, they pass through narrow anatomical passageways – the osteofibrous tunnels– that redirect their course.

The floor of these tunnels consists of bone, whereas the roof is made of focal thickenings of the fascia, the so-called “retinacula”, which prevent dislocation and traumatic damage of the structures contained in the tunnel during joint activity. In normal states, color and power Doppler US are able to depict blood flow signals from perineural and interfascicular vessels only occasionally and in large nerve trunks.

Careful scanning technique of nerves based on the precise knowledge of their position and analysis of their anatomical relationships with surrounding structures is essential. Systematic scanning on short axis planes is preferred to follow the nerves contiguously throughout the limbs. Once detected, the nerve is followed proximally and distally shifting the transducer up or down according to its course. With this technique – called the “lift technique” – the examiner is able to explore long segments of a nerve in a few seconds throughout the limbs and extremities.

In the event of intrinsic or extrinsic nerve abnormalities, the US examination is more appropriately focused on the area-of-interest using oblique and longitudinal scanning planes.all main nerves can readily be displayed in the extremities due to their superficial position and absence of intervening bone, depiction of the peripheral nervous system is not possible verywhere with US.

In fact, most cranial nerves, the nerve roots exiting the dorsal, lumbar and sacral spine, the sympathetic chains and the splanchnic (visceral) nerves in the abdomen cannot be visualized due to their course being toodeep or interposition of bony structures.

Dermis and hypodermisFrom an anatomical point of view, nerves are characterized by a complex internal structure made of nervous fibers (containing axons, myelin sheaths and Schwann cells) grouped to form fascicles, and loose connective tissue (containing elastic fibers and vessels)

The skin represents the external covering of the whole body. Its thickness varies according to different body regions, reaching a maximum thickness at the palm of the hand and the sole of the foot. The skin is divided into two ifferent layers; • The external layer is the epidermis• The internal layer the dermis

The epidermis; consisting of squamous multi-stratified epithelium that continues deeply with the dermis,The dermis; a layer of connective tissue made of cells and collagen fibers lying in an amorphous (without shape) interstitial substance. The dermis contains blood vessels, nerves, lymphatics, hair follicles and glands.

The hypodermis is found even more deeply and it is made of a tissue rich in collagen fibers and connected to the dermis by fibrous branches. The hypodermis has a complicated structure containing adipose storage inside the subcutaneous adipose tissue. The hypodermal thickness varies according to the examined region and to the patient’s personal constitution

Detailed US exploration of the skin is now possible due to high frequency and high resolution transducers. The skin appears as a hyperechoic superficial band of variable thickness and homogeneous structure where it is not possible to differentiate the epidermis from the dermis by ultrasound.

The hypodermis, on the contrary, is easily identifiable: it appears as a deep hypoechoic layer, characterized by intersecting curvilinear septa, that correspond to supporting fibrous branches, containing blood vessels well-depicted by color Doppler techniques.

The hypodermis is separatedfrom the underlying muscular layer by the superficial aponeurotic fascia, appearing as a double hyperechoic line. Dynamic examination is useful to differentiate adipose from musculartissue

To diagnose skin disease, the main investigation tends to be clinical examination, eventually supported by histological analysis; US can be useful as a follow-up examination when assessing systemic diseases with skin involvement, such as systemic sclerosis (scleroderma).

Subcutaneous tissue ultrasound examination can also be useful in the diagnosis and staging of some neoplastic lesions such as melanoma, glomus tumours and hemangiomas. It is also used for anthropometric studies in sports medicine to calculate the fat-free mass, which represents an important indicator of physical condition for athletes.

epidermis-dermis (E), hypodermis (H) and superficial aponeurotic fascia (A)

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