Download - Thyroid ultrasound

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متنا انك انت العليُم الحكيمما علا لا ا Surah Al Baqarah verse 32

http://www.quran4theworld.com/transliteration/2_31-60.HTM

اسالم علیمکWelcome to THYROID

By: Dr. Raham BachaMD KMU

MSc Sonology Gold Medalist

(UOL)

The university of

Lahore

OBJECTIVE•INDICATION OF THYROID SCANNING

•THYROID ANATOMY

•SCANNING TECHNIQUES

•SONOGRAPHIC ANATOMY

•THYROID PATHOLOGIES

•CHARACTERIZATION OF THYRIOD NODULES

•DIFFUSE THYROID DISEASES

1.To confirm presence of a thyroid nodule whenphysical examination is equivocal.

2.To characterize a thyroid nodule(s), i.e. tomeasure the dimensions accurately and toidentify internal structure and vascularization.

3.To differentiate between benign and malignantthyroid masses, based on their sonographicappearance.

4.To differentiate between thyroid nodules andother cervical masses like lymphadenopathy,thyroglossal cyst and cystic hygroma.

INDICATIONS

INDICATIONS

5. To evaluate diffuse changes in thyroidparenchyma.

6. To detect post-operative residual or recurrenttumor in thyroid bed or metastases to neck lymphnodes.

7. To screen high risk patients for thyroidmalignancy like patients with history of familialthyroid cancer, multiple endocrine neoplasia(MEN) and irradiated neck in childhood.

8. To guide diagnostic (FNA cytology/biopsy) andtherapeutic interventional procedures.

ANATOMY

Ultrasound Examination Technique

All patients are examined in supine position withhyperextended neck, using a high frequency lineararray transducer (7-15 MHz) that providesadequate penetration and high resolution image.Scanning is done both in transverse andlongitudinal planes. Real time imaging of thyroidlesions is performed using both gray-scale and colorDoppler techniques. The imaging characteristics ofa mass (viz. location, size, shape, margins,echogenicity, contents and vascular pattern) shouldbe identified.

Normal Anatomy

The normal thyroid gland consists of twolobes and a bridging isthmus. Thyroid size,shape and volume varies with age and sex.Normal thyroid lobe dimensions are: 18-20mm longitudinal, 10-12mm antero-posterior(AP) diameter and 8-9mm in width, innewborn; 25 mm longitudinal and 12-15 mmAP diameter at one year age; and 40-60 mmlongitudinal, 20-30mm in AP diameter and13-18 mm width in adult population.

The limits of normal thyroid volume(excluding isthmus, unless its thickness is >30mm) are 10-15 ml for females and 12-18 ml formales.

The relationships with surrounding structuresare: sterno-cleido-mastoid and strap musclesanteriorly; trachea/esophagus and longus collimuscles posteriorly; and common carotidarteries and jugular veins bilaterally

Thyroid volume (ml)= 𝐿 ×𝑊 × 𝐷 × 0.52

Color and power Doppler ultrasound (US) areuseful to evaluate vascularity of the thyroidgland and focal masses. Thyroid gland is ahighly vascular structure supplied by superiorand inferior thyroid arteries. The thyroidarteries can be visualized on color Dopplerexamination while the flow parameters fromthese vessels can be measured by spectralDoppler examination.

Normally, a low resistance flow with highpeak systolic velocity (PSV) is detected inthese vessels on spectral Doppler analysis.The normal PSV in intra thyroid arteriesranges between 15-30 cm/second, but it canrise in certain pathologies (like Graves'disease) to over 100 cm/sec

Congenital and Developmental Anomalies of Thyroid Gland

The thyroid gland primordium develops frommedian eminence in the floor of primitive pharynx(a point later known as foramen cecum at the baseof tongue) during 4th week of gestation. Fromforamen cecum, the primitive primordium descendsthrough anterior midline portion of the neck toreach its final position below thyroid cartilage by7th week of gestation.

During this descent, the developing thyroidgland retains an attachment to the pharynx bya narrow epithelial stalk known asthyroglossal duct. This duct usually becomesobliterated by 8th -10th week of gestation.Thyroid hormone synthesis normally beginsat about 11th week of gestation

Occassionally, rests of thyroid tissue mayremain along the course of thyroglossal duct,giving rise to an additional thyroid lobe, thepyramidal lobe, attached to distal end of thethyroglossal duct and left side of isthmus(seen in 50% of population). Persistence ofthyroglossal duct results in formation ofthyroglossal cyst, which clinically presents asmidline neck swelling or lump, usually foundat level of hyoid bone or thyroid cartilage.

On ultrasound, the cyst appears as awell-defined anechoic to hypoechoiclesion with posterior acousticenhancement. Internal echoes may beseen within the cyst due tohemorrhage or infection.

Ectopic thyroid represents an arrest inusual descent of part or all of the thyroidtissue along the normal pathway. Ectopicthyroid gland develops most commonly atsublingual (midline at foramen cecum),suprahyoid or infrahyoid position. USGshows presence of an ectopic thyroidtissue and the normal thyroid gland mayor may not be present at normal position.

Ectopic thyroid may be easily detected on CTand radionuclide scans. Congenital agenesisor hypoplasia (unilobar type or of isthmus) ofthe thyroid gland may occur due todevelopmental failure of all or part of thyroidgland. On USG, agenesis of isthmus ischaracterized by absence of isthmus with thelateral lobes positioned independently oneither side of the trachea.

Diseases of Thyroid Gland

The incidence of all thyroid diseases is higherin females than in males. Nodular thyroiddisease is the most common cause of thyroidenlargement. Majority of patients with thyroiddisease present with midline neck swelling,occasionally causing dysphagia andhoarseness of voice.

Broadly the thyroid diseases are classified into three categories:

•(i) benign thyroid masses,

•(ii) malignant tumors of thyroid gland, and

•(iii) diffuse thyroid enlargement

Thyroid Nodule(s)Nodularity within thyroid is normal. The incidenceand development of nodules correlate directly withage of the patient and is regarded as a part ofnormal maturation process of the thyroid gland. Theincidence of thyroid nodules is very high on USG,ranging from 50% to 70%. Thyroid cancer accountsfor less than 7% cases. Although there is someoverlap between ultrasound appearance of benignand malignant nodules, certain USG features arehelpful in differentiating the two.

The most common cause of benign thyroid nodule isnodular hyperplasia. Thyroid adenomas are othercommon benign neoplasms of thyroid that aremostly solitary but may also develop as a part ofmultinodular masses. Iso-or hyper-echogenicity ofthe thyroid nodule in conjunction with a spongiformappearance is the most reliable criterion forbenignity of the nodule on gray-scale ultrasoundand.

Other features to characterize nodule

•size <1 cm, width > length. Size of the nodule is also helpful. The size of the nodule increase with age, so follow up is helpful. Although 90 percent of the benign nodules can also increase in volume by 50% in 5 years.


•Texture: thyroid nodules may either be hypo echoic, Isoechoic or hyperechoic. It may be solid, cystic or mixed.

•Hyperechoic nodules with internal cystic areas are benign in nature. But hyper echoic nodule with thick external hollow is a sign of malignant nodule. But hyper echogenicity without thick peripheral hallow is a strong feature of benign nodule.

•Malignant nodules are mostly hypoechoic but it is not necessary for all hypoechoic nodules to be malignant. Because most of the thyroid nodules are benign in nature that’s why most of the hypoechoic nodules are benign

"Ring down" or "comet-tail" artifact is a typicalsign of benign cystic colloid nodule. Perinodularflow or spoke-and-wheel-like appearance ofvessels on color Doppler examination ischaracteristic of a benign thyroid nodule.However, this flow pattern may also be seen inthyroid malignancy. A complete avascular noduleis very unlikely to be malignant.


• Calcification: calcification is common in benign as well as in malignant nodules but it is more probably malignant if found in solitary nodules.

• Micro calcination <2mm is most commonly found in malignant nodule.

Histologically, malignant tumors of thethyroid are classified as papillary carcinoma(60-80%), follicular carcinoma (20-25%),medullary carcinoma (4-5%), anaplasticcarcinoma (3-10%), lymphoma (5%) andmetastases. The overall sensitivity of thyroidultrasound for diagnosing a malignant noduleis 83.3%.

USG features predictive of malignant nodulesinclude presence of microcalcifications (<2mm), local invasion, lymph node metastases,marked hypoechogenicity, irregular margins,solid composition, absence of a hypoechoichalo around the nodule, size >1 cm, taller-than-wide-shape, and an intra nodularvascularity

Multiplicity of the nodule is not an indicatorof benignity. The incidence of malignancy issame in solitary nodules as it is in multiplenodules. Interval growth of nodules is a non-specific characteristic. Microcalcifications aremost commonly found in papillary andmedullary carcinoma thyroid and in theirmetastases (lymph node or hepatic).

On USG, microcalcifications appear aspunctuate hyperechoic foci with or withoutposterior acoustic shadowing. Rarely,microcalcifications can be found in follicularand anaplastic thyroid carcinomas and certainbenign lesions like follicular adenoma,multinodular goitre and Hashimoto'sthyroiditis.


• Margins

• Margins may be smooth, speculated, micro-labulated, or Ill defined. Spiculated margins are strongly suggestive of malignancy.


•presence of hypoechoic halo•It is caused either by nodular capsule or by the compression of the thyroid tissue.

•It may either be thin or thick and regular or irregular

•Thin and regular is suggestive of benign

•While thick and irregular more probability of malignancy.


•Vascularity•There are three patern of vascular distribution in the tumer.

•Type one: absence of flow

•Type two: peripheral vascularity

•Type three: internal flow. ( associated with malignancy)

Local invasion of adjacent structures andmetastases to regional cervical lymph nodesare highly specific signs of thyroidmalignancy. They occur more frequently inmedullary carcinoma (50% cases) thanpapillary carcinoma (40% cases). Althoughpatients with thyroid carcinoma may presentwith multiple level nodal disease, theanterolateral group (level II, III and IV) havegreatest risk of metastatic disease.

Lymph nodes involment.

US neck plays an integral role in themanagement of cervical metastases from thyroidcarcinoma (ranging from selective removal to acomprehensive neck dissection) by evaluatingnodal metastases with respect to node level.Anaplastic thyroid carcinoma and lymphoma arehighly aggressive tumors, early and extensivelocal invasion is common with these tumors.Lymph node metastasis is rare in follicularthyroid carcinoma, even in highly invasivecases.

The most common pattern of vascularity inthyroid malignancy is marked intrinsichyper vascularity. On color Dopplerexamination, more flow is demonstrated inthe central portion of the tumor than in thesurrounding thyroid parenchyma

Increased vascularity with distortion of sinus fatis seen within the metastatic lymph nodes.Thyroid lymphomas are hypo-vascular withchaotic vessels; however, neck vesselencasement may be present.

Metastases to the thyroid gland areinfrequent. The main primary tumorsspreading to the thyroid gland are malignantmelanoma (39% of cases), breast carcinoma(21% of cases) and renal cell carcinoma(10% of cases). Sonographically, metastasespresent as a solitary or multiple hypoechoichomogeneous mass(es) withoutcalcification.

Thyroid nodule(s) with suspicious USGfeatures should be investigated further withFNA biopsy. Moreover, the work-up ofasymptomatic thyroid nodules(incidentalomas) must be weighed againsthigh prevalence of benign thyroid nodulesand low mortality rate from small thyroidcarcinomas.

Diffuse Thyroid DiseasesThe common conditions that present as diffuseenlargement of the thyroid gland includemultinodular goitre, Hashimoto's (lymphocytic)thyroiditis, de-Quervain's subacute thyroiditis andGraves' disease. The sonographic features of theseprocesses may be similar but they have differentbiochemical profile and clinical presentations.Hence, in these conditions, ultrasound findingsshould be viewed in relation to clinical andbiochemical status of the patient..

Multinodular goitre (MNG) is the commonest causeof diffuse asymmetric enlargement of the thyroidgland. Females between 35-50 years of age aremost commonly affected. Histologically, colloid oradenomatous form of MNG is common. Theultrasound diagnosis rests on the finding ofmultiple nodules within a diffusely enlarged gland.A diffusely enlarged thyroid gland with multiplenodules of similar US appearance and with nonormal intervening parenchyma is highlysuggestive of benignity, thereby making FNAbiopsy unnecessary.

Multinodular goitre (MNG)

Most of the nodules are iso-or hyper-echoic innature; when enlarged provide heterogeneousecho pattern to the gland. These goitrousnodules often undergo degenerative changesthat correspond to their USG appearances:cystic degeneration gives anechoic appearanceto the nodule, hemorrhage or infection withinthe cyst is seen as moving internalechoes/septations, colloidal degenerationproduces comet-tail artifact, while dystrophiccalcification is often course or curvilinear.

Vascular compression due to follicular hyperplasialeads to focal ischemia, necrosis and inflammatorychange. The assessment of nodule vascularity isvery useful in differentiating MNG frommultifocal carcinoma. Nodule with intrinsicvascularity and other features of malignancy canbe targeted for biopsy, in preference to othernodules.

• Graves' disease (thyrotoxicosis) is anautoimmune disease characterized bythyrotoxicosis.

• Females between 20 and 50 years are mostcommonly affected.

• On gray-scale USG, thyroid is diffusely enlarged(2-3 times its normal size), hypoechoic andheterogeneous.

• Color flow imaging reveals a spectacular "thyroidinferno" with marked hyper vascularity

• This pattern demonstrates extensive intra-thyroidflow both in systole and diastole.

In contrast to Hashimoto's thyroiditis,return of normal thyroid appearance ispossible at the time of remission. Theultrasound picture of Graves' disease maybe indistinguishable from Hashimoto'sthyroiditis and de-Quervain's thyroiditis;however, clinical picture variessignificantly between these threeconditions.

Hashimoto's thyroiditis(chronic lymphocytic thyroiditis) is anautoimmune disorder leading to destruction of thegland and results hypothyroidism. It occurspredominantly in females over 40 years of age.Painless, diffuse enlargement of thyroid gland isthe most common clinical presentation. Clinically,Hashimoto's thyroiditis may present withformation of goitre with or without disturbance ofthyroid function.

Children with hypothyroidism usually havegrowth failure and delayed puberty. Diagnosis ofHashimoto's thyroiditis is confirmed bydemonstration of serum thyroid antibodies andantithyroglobulin antibodies. The characteristicUS appearance is focal or diffuse glandularenlargement with coarse, heterogeneous andhypoechoic parenchymal echo pattern.

Presence of multiple discrete hypoechoicmicronodules (1-6 mm size) is stronglysuggestive of chronic thyroiditis. Fineechogenic fibrous septae may produce apseudolobulated appearance of theparenchyma. Color Doppler maydemonstrate slight to markedly increasedvascularity of the thyroid parenchyma.Increased vascularity seems to beassociated with hypothyroidism, likely dueto trophic stimulation of thyroid-stimulating hormone.

Small atrophic gland represents end stageHashimoto's thyroiditis. Occasionally, nodularform of Hashimoto's thyroiditis may occur;within a sonographic background of diffuseHashimoto's thyroiditis or within normalthyroid parenchyma. Both benign and malignantnodules are known to co-exist within abackground of diffuse Hashimoto's thyroiditis;on ultrasound, hyperechoic nodules are morelikely to be benign, whereas hypoechoicnodules are more likely to be malignant

However, a PET scan or FNAC may be requiredto differentiate them. The abnormal thyroidultrasound picture in Hashimoto's thyroiditisnever improves and remains unchanged for rest ofthe patient's life. Hashimoto's thyroiditis isassociated with an increased risk of thyroidmalignancies like follicular or papillarycarcinoma and lymphoma. Moreover, in patientsof Hashimoto's thyroiditis, USG examination mayreveal presence of perithyroidal satellite lymphnodes, especially the "Delphian" node justcephalad to the isthmus

These perithyroidal lymph nodes areextremely useful in diagnosis of the thyroiditiswhen correlated with USG, clinical andlaboratory findings. However, it should bekept in mind that these lymph nodes may alsocorrespond to underlying malignant processes,like thyroid malignancy and lymphoma, inpatients with Hashimoto's thyroiditis. Indoubtful cases, FNA biopsy may be requiredto differentiate between benign(reactionary/inflammatory origin) andmalignant lymph nodes

De-Quervain's thyroiditis(subacute granulomatous thyroiditis)characteristically presents with painful swellingin lower neck, fever and constitutionalsymptoms, typically following a viral illness.There may be features of thyrotoxicosis orhypothyroidism depending on phase of theillness. Initially there is thyrotoxicosis, followedby hypothyroidism. USG examination showscharacteristic focal hypoechoic areas (map like)and enlargement of one or both thyroid lobes.

Level VI chain lymph nodes (pre-tracheal, thepreferential site of thyroid drainage) are found tobe enlarged in majority of patients. ColorDoppler sonography shows decrease or absentblood flow within abnormal map-likehypoechoic areas. Complete recovery ischaracteristic and occurs in weeks to months. Inrecovery phase, thyroid appearance returns tonormal.

Acute thyroiditis(suppurative/infectious thyroiditis) is rareand occurs due to suppurative (pusforming) infection of the thyroid. Inchildren and adults, the most commoncause is infection of pyriform sinus fistula(a congenital branchial pouch abnormality).In elderly, long standing goitre anddegeneration in thyroid malignancy are riskfactors.

Clinically, patient presents with acute onsetfever, thyroid pain, asymmetric swelling ofthe gland (predominantly left sided) andregional lymphadenopathy (level VI cervicalchain lymph nodes). On USG, the involvedlobe appears heterogeneous and hypoechoic.Abscess and cyst formation may be seen.Rarely, retropharyngeal abscess, trachealobstruction, jugular vein thrombosis andmediastinitis may complicate acutethyroiditis

Riedel's thyroiditis(chronic fibrous thyroiditis/invasive fibrousthyroiditis) is the rarest type of inflammatorythyroid disease. The thyroid gland isgradually replaced by fibrous connectivetissue and becomes extremely hard. It mayencase the adjacent vessels or maycompress, displace or deform shape of thetrachea. On ultrasound, Riedel's thyroiditismay present as a diffuse hypoechoic processwith ill-defined margins and marked fibrosis

Diagnostic PitfallsCystic components of thyroidmalignancies may be mistaken for benigncyst or cystic degeneration in a benignnodule. A careful ultrasound assessment todemonstrate solid component withvascularity or solid excrescence withmicrocalcifications will be of help indifferentiating these lesions.

Diagnostic Pitfalls

Cystic or calcified lymph node metastases adjacentto the thyroid gland may be mistaken for benignnodule in multinodular thyroid disease. Incompleterim of thyroid parenchyma around the mass andlack of movement of the mass with the thyroidgland during swallowing favors extrathyroid lymphnodal metastasis. Cystic metastatic nodes are morecommon in papillary carcinoma thyroid, whilecalcified metastatic nodes are found both inpapillary and medullary carcinoma thyroid.

Diagnostic Pitfalls

Diffusely infiltrative hyper vascular thyroid carcinoma likepapillary or follicular carcinoma may be mistaken forautoimmune thyroid disease (such as Graves' disease orHashimoto's thyroiditis); similarly multifocal carcinomamay be mistaken for benign multinodular goitre. Asdescribed earlier, diffuse thyroid enlargement with multiplenodules of similar US appearance and with no normalintervening parenchyma is highly suggestive of benignity.US features that suggest malignancy include irregular ornodular enlargement of the thyroid gland, local invasionand nodal metastases. Co-existing autoimmune thyroiddisease and thyroid carcinoma can further complicate the

situation

Therapeutic Application

US-guided percutaneous ethanol injection (EPI) isused for sclerosation of autonomous and toxicthyroid adenomas. Post-injection follow-upultrasound scan demonstrates significant reductionin nodule size on gray-scale imaging, and markedreduction or complete absence of intra nodular flowon color and power Doppler examination. Periodicneck ultrasound is the most sensitive method fordetecting recurrence of thyroid carcinomas after

thyroidectomy.

Advanced Ultrasound Techniques in Thyroid Imaging

Ultrasound elastography is a dynamic technique thatestimates stiffness of tissues by measuring the degreeof distortion under external pressure. Thyroid glandelastography is used to study hardness/elasticity of thethyroid nodule to differentiate malignant from benignlesions. A benign nodule is softer and deforms moreeasily, whereas the malignant nodule is harder anddeforms less when compressed by ultrasound probe.


The elastography technique utilizes externalcompression to differentiate malignant thyroidnodules from benign lesions. It determines theamount of tissue displacement at various depths, byassessing the ultrasound signals reflected from thetissues before and after compression. Dedicatedsoftware then provides an accurate measurement oftissue distortion and displays it visually as anelastographic image.


The elastographic image (elastogram) displayedover the B-mode image in a color scale, indicateslocal tissue elasticity as (i) very soft in blue colorfor tissue with greatest elastic strain and (ii) veryhard in red color for tissue with no strain. Real-timeshear elastography is a latest technique; thatcharacterizes and quantifies tissue stiffness betterthan conventional elastography.


Cystic lesions and calcified nodules are excludedfrom US elastographic evaluation. USelastography helps in characterizing acytologically indeterminate nodule as malignant orbenign with high accuracy that is almostcomparable to FNAC and obviates the need ofunnecessary FNA examination. The majorlimitation of US elastography is that it cannotassess the lesions which are not surrounded byadequate normal tissue.


Contrast-enhanced ultrasound (CE-US) is a newlydeveloped technique that helps in characterizing a thyroidnodule. On CE-US, enhancement patterns are different inbenign and malignant lesions. Ring enhancement ispredictive of benign lesions, whereas heterogeneousenhancement is helpful for detecting malignant lesions.However, overlapping findings seem to limit the potentialof this technique in the characterization of thyroidnodules. Use of specific contrast (e.g. Sono Vue) andpulse inversion harmonic imaging further improves theefficacy of ultrasound in diagnosing a malignant thyroidnodule.

Current Status of US Elastographyand CE-USG in Characterisation of

Thyroid Nodules

Several studies have been conducted to evaluate therole of ultrasound using elastography and contrastagent in the characterisation of thyroid nodules.


Thyroid NodulesA study (done on 23 thyroid nodules) was conducted byFS Ferrari et al. in 2008, to differentiate benign frommalignant thyroid nodule, using both elastography andCE-US. Elastography yielded a sensitivity of 88%,specificity of 78%, positive predictive value (PPV) of71%, negative predictive value (NPV) of 91% anddiagnostic accuracy (DA) of 82%; and CE-US yielded asensitivity of 100%, specificity of 71%, PPV of 69%,NPV 100% and DA of 83%


Thyroid Nodules

Another study (sample size 90) was done by Y Honget al. in 2009 to evaluate the diagnostic utility of real-time ultrasound elastography in differentiating benignfrom malignant thyroid nodules. According to thisstudy, elastography yielded a sensitivity of 88%,specificity of 90%, PPV of 81% and NPV 93%


Thyroid NodulesA recent study (done on 703 thyroid nodules) publishedby Moon et al. in 2012 evaluated the diagnosticperformance of gray-scale US and elastography indifferentiating solid thyroid nodules. According to thestudy, the sensitivity and NPV for differentiating benignfrom malignant thyroid nodules on gray scale US are91% and 94.7% respectively, and on US elastographyare 65.4% and 79.1% respectively. They concluded thatelastography alone or in combination with gray scale USis not a useful tool in differentiating benign frommalignant thyroid nodules.


Thyroid Nodules

Another study (sample size 72) has been done recently byM Giusti et al. in 2012, in which they have evaluated therole of ultrasound, elastography and CE-US in screening ofthyroid nodules. They found that the ultrasound scoreshowed high specificity and PPV when compared withelastography and CE-US. Both elastography and CE-USwere expensive, time consuming and of limited utility inselecting patients for thyroidectomy


Thyroid Nodules

In short, some studies show very high sensitivity andspecificity of US elastography; in the range of 85-90%.On the contrary, there are studies which show itssensitivity as low as 65% and less (compare from thesensitivity of gray-scale US which is in the range of 90to 95%).


Thyroid Nodules

Thus, although elastography and CE-US appear promisingimaging techniques, they need to be standardized. At present,they seem to be expensive, time consuming and of limitedutility in selecting patients for surgery. Larger prospectivestudies are needed to establish the diagnostic accuracy andcost effectiveness of these techniques over conventional grayscale and color Doppler imaging

ConclusionHigh-resolution USG has improvedin the past few years and hasbecome a very valuable diagnostictool in the evaluation of thyroiddiseases. Recent advances in thyroidultrasound have further improvedthe diagnostic accuracy

Conclusion

It is the imaging modality of choice for evaluating thyroid masses in

children and pregnant females. Real time USG also helps to guide the

diagnostic and therapeutic interventional procedures in various

thyroid diseases.

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