considerations regarding the role of 99m tc-tetrofosmin thymic scintigraphy in thymomas

Lidia Ionescu, Cipriana Stefanescu, Carmen Vulpoi, C. Diaconu, Cr. Dragomir

CT –mainstay of thymic investigation

Thoracic CT scan has a reliable sensitivity and specificity in detecting thymic lesions

Elective method of diagnosis

One major difficulty is to differentiate for certain between thymic lymphoid hyperplasia and thymoma.

But in equivocal cases, other investigations can add suplimentary informations.

MV, male, 46 years old, 6w. history of MG- Oss. III, CT suspicious for thymoma, Op. 2004, pathology- thymic lymphoid hyperplasia + mediastinal ectopies, post. op.- complete remission

GE, 19 years old man Hashimoto’s thyroiditis - apr. 2005- L-thyroxine, Hemolytic anemia – oct .2005 (Hb-3,8g/dl, LDH-1444 u/l)-Treatment- steroizi, transfuzii repetate.CT- thymoma, op.dec 2005 Pathology- thymic lymphoid hypertrophy, Result- complete remission of hemolytic anemia

PF, female, 21 years old, MG- OSS III, CT- thymic hyperplasia, op. 1997Pathology - lymphocitic thymoma Result - farmacologic remission

Imaging investigationsEquivocal cases - thymic scintigraphy can

add supplimentary informations to CT aspects.

Equivocal cases: Association of thyro-thymic lesionsTumor recurrenceType of thymic lesionsEctopic thymomas

Scintigraphy with 99mTc-tetrofosminFrequently used in the assessment of myocardial

perfusion, conducted to incidental extracardiac uptake and detection of a mediastinal mass as it showed in few reported cases in the literature (Kotsalou I, Hawkins M)

This investigation is not yet included in the algorithm of diagnosis for mediastinal mass

But it must be considered a valuable alternative when conventional investigations fail to confirm a clinical suspicion, resulting in adequate decision making.

Thymic scintigraphyPathological uptake of 99mTc tetrofosmin

appears in benign and malignant tumors through an incomplete understood mechanism.

But the increased number of mitochodrias and the degree of perfusion of the lesion seem to play an important role.

Thymic scintigraphy

Thymic scintigraphy can asses after the degree of up-take of the radiotracer on the early and late imagesNormal thymus, Hyperplasia ThymomaTumor recurrenceEctopic thymomas

The 99m-Tc Tetrofosmin scintigraphy

Performed with standard doses, according to the worldwide accepted protocol.

An informed consent for the investigation is obtained from all the patients.

An AXIS Gamma camera (Philips), Siemens double-head detection and SPECT was used and acquired data were analyzed with an IBM specialized software.

99m Tc Tetrofosmin

Lipophile molecule that crosses the cellular membranes according to electrochemical gradient and fluidity of the membrane.

It accumulates mainly in the mitochondria, which explains the fixation in cells with intense metabolism.

Equivocal casesThe association hyperthyroidy-myasthenia

gravis is present mainly in autoimmune thyropathies such as Hashimoto’s thyroiditis or Grave’s disease

Usually myasthenia gravis is secondary to hyperthyroidy due to thymus hyperplasia and an adequate antithyroid drug treatment or surgery result in remission of thymic hyperplasia.

Associated lesionsGrave’s disease-myasthenia gravis

Murakami, Yasuhiro Hosoi demonstrated the presence of thymic hyperplasia in Grave’s disease patients, calculating on CT scan images the size and density of the thymus on untreated and treated Grave’s disease patients.

The conclusion was that thymic hyperplasia regresses in treated patients either with antithyroid drugs or total thyroidectomy

Thyro-thymic lesions Yamanaka K, Nakayama H. reported a case

of Grave's disease associated with a mediastinl mass in whom CT scan RMI were suggestive for a thymoma.

The patient underwent total thyroidectomy and thymectomy at the same stage.

Pathology report showed a thymic hyperplasia.

AM, 46-year-old woman, 2007 multinodular goitre and myasthenia gravis Thyroid profile (TSH-0.1 µUI/ml, fT4-1.2ng/dl), Thyroid total volume of 65.9 ml. (Prof. dr. C. Vulpoi) Compressive goiter Retrosternal goiter

Total thyroidectomy for MNG-2007,Myasthenia gravis aggravated

Normal Chest Normal thymus

Thymic scintigraphyHypercaptation of 99mTc-tf. consistent with a thymoma

Repeat CT scanAntero- inferior mediastinal massThymectomy, 6 months following TT, june 2008

Paramedian low retrosternal mass Well-encapsulated mass

Hyperthyroidism+ectopic thymomaThe thyroid lesion more obvious, was first treated

and myasthenia gravis considered wrongly to be secondary and remitting after total thyroidectomy.

On thymic scintigraphy was evident the high uptake of Tc-TF in lower anterior mediastinum with a high suspicion of thymoma.

Pathology report of the specimen was mixt thymoma with capsular microscopic invasion-Masaoka II stage.

Equivocal case

Tumour recurrence or postoperative mediastinal scar in patients with recurrent myasthenia gravis??

CT, 64 years old, thymoma+MG, Oss.IV, op. 2002, Lymphocitic thymoma (type I malignant thymoma)-Masaoka II ( well encapsulated but microscopic capsular invasion), adhesions to left M. pleura which was resected

Radiotherapy 44 Gy, chemotherapy, 1 year CP+PDNPericarditis at 1 year postRxTRemission of MG 5 years, 2008- AChE

CT aspects-2009Retrosternal postoperative scar tissue, pericarditis

2009Inflammatory pericarditis

2009- POSTOPERATIVE THYMIC SCINTIGRAPHYLACK OF RADIOTRACER UPTAKE IN THE ANTERIOR MEDIASTINUM

Conclusion

The thymic 99mTc tetrofosmin scintigraphy can be efficient in diagnosing and therapeutic decision making when conventional imaging investigations fail to confirm a clinical suspicion.