Considerations regarding the role of 99m Tc-tetrofosmin thymic scintigraphy in thymomas

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Considerations regarding the role of 99m
Tc-tetrofosmin thymic scintigraphy in thymomas

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

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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.

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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
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GE, 19 years old man Hashimotos 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
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PF, female, 21 years old, MG- OSS III, CT-
thymic hyperplasia, op. 1997Pathology -
lymphocitic thymoma Result - farmacologic
remission
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Imaging investigations

• Equivocal cases - thymic scintigraphy can add
  supplimentary informations to CT aspects.
• Equivocal cases
• Association of thyro-thymic lesions
• Tumor recurrence
• Type of thymic lesions
• Ectopic thymomas

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Scintigraphy with 99mTc-tetrofosmin

• Frequently 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.

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Thymic scintigraphy

• Pathological 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.

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Thymic scintigraphy

• Thymic scintigraphy can asses after the degree
  of up-take of the radiotracer on the early and
  late images
• Normal thymus,
• Hyperplasia
• Thymoma
• Tumor recurrence
• Ectopic thymomas

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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.

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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.

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Equivocal cases

• The association hyperthyroidy-myasthenia gravis
  is present mainly in autoimmune thyropathies such
  as Hashimotos thyroiditis or Graves 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.

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Associated lesionsGraves disease-myasthenia
gravis

• Murakami, Yasuhiro Hosoi demonstrated the
  presence of thymic hyperplasia in Graves disease
  patients, calculating on CT scan images the size
  and density of the thymus on untreated and
  treated Graves disease patients.
• The conclusion was that thymic hyperplasia
  regresses in treated patients either with
  antithyroid drugs or total thyroidectomy

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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.

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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

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Total thyroidectomy for MNG-2007,Myasthenia
gravis aggravated

• Normal Chest

• Normal thymus

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Thymic scintigraphyHypercaptation of 99mTc-tf.
consistent with a thymoma
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Repeat CT scanAntero- inferior mediastinal
massThymectomy, 6 months following TT, june 2008

• Paramedian low retrosternal mass

• Well-encapsulated mass

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Hyperthyroidismectopic thymoma

• The 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.

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Equivocal case

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

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CT, 64 years old, thymomaMG, 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
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Radiotherapy 44 Gy, chemotherapy, 1 year
CPPDNPericarditis at 1 year postRxTRemission
of MG 5 years, 2008- AChE
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CT aspects-2009Retrosternal postoperative scar
tissue, pericarditis
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2009Inflammatory pericarditis
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2009- POSTOPERATIVE THYMIC SCINTIGRAPHYLACK OF
RADIOTRACER UPTAKE IN THE ANTERIOR MEDIASTINUM
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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.
•  

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