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Year : 2020  |  Volume : 63  |  Issue : 4  |  Page : 608-610
Thymic amyloidoma mimicking sclerosing thymoma in a triple vessel disease patient: An incidental finding

1 Department of Pathology, Adesh Institute of Medical Sciences and Research, Bathinda, Punjab, India
2 Focus Imaging and Research Centre Pvt Ltd., Laboratory Medicine Division, New Delhi, India
3 Department of Pathology, Government Medical College and Hospital, Sector 32-A, Chandigarh, India

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Date of Submission02-Jun-2019
Date of Decision26-Dec-2019
Date of Acceptance30-Dec-2019
Date of Web Publication28-Oct-2020


A 65 year old man who underwent coronary artery bypass graft (CABG) for triple vessel disease was found to have enlarged thymus. Biopsy of the thymic mass revealed localised amyloid deposits demonstrating strong apple green birefringence on polarised microscopy. Localized thymic amyloidosis is an extremely rare finding with present case as the seventh in the world and the first in India. Review of literature of thymic amyloidoma and its close differential sclerosing thymoma is hereby described.

Keywords: Amyloidosis, birefringence, microscopy, thymus

How to cite this article:
Dhingra H, Singh A, Baliyan A, Bansal V. Thymic amyloidoma mimicking sclerosing thymoma in a triple vessel disease patient: An incidental finding. Indian J Pathol Microbiol 2020;63:608-10

How to cite this URL:
Dhingra H, Singh A, Baliyan A, Bansal V. Thymic amyloidoma mimicking sclerosing thymoma in a triple vessel disease patient: An incidental finding. Indian J Pathol Microbiol [serial online] 2020 [cited 2022 May 18];63:608-10. Available from: https://www.ijpmonline.org/text.asp?2020/63/4/608/299307

   Introduction Top

Thymic lesions are mostly accountable for anterior mediastinal lesions. Thymic epithelial tumors are a chief concern for asymptomatic incidental anterior mediastinal lesions.[1] An abnormal appearance of the thymus may occur either due to diffuse gland enlargement or a distinct mass. Both benign thymic hyperplasia and lymphoma can cause diffuse thymic enlargement. Many lesions including thymoma, thymic carcinoma, thymic carcinoids, and benign lesions such as thymolipomas and cysts present with a focal thymic mass.[2]

Amyloidosis in the thymus is extremely rare.[3] It is usually a systemic disease (80–90%) but 10–20% of cases are localized.[4],[5] Localized deposits are limited to a single organ or tissue, without the involvement of any other site in the body. Amyloidoma is a term that defines a mass having amyloid deposits. The deposits may produce grossly detectable nodular masses or are found only on microscopy. Nodular amyloid deposits are mostly noted in the respiratory tract (nasopharynx, lung, larynx), skin, urinary bladder, tongue, lip, colon, nails, and orbit.[3],[6],[7],[8]

This case report describes an incidentally found thymic amyloidoma in a 65-year-old man who underwent coronary artery bypass graft (CABG) for triple vessel disease. Herein, we describe the literature review of thymic amyloidoma and its close differential sclerosing thymoma.

   Case History Top

A 65-year-old man was admitted to the department of cardiothoracic surgery for chest pain. Triple vessel disease was diagnosed with coronary angiography. The patient was advised CABG. Intraoperatively, the thymus was found to be enlarged. Biopsy of the thymic mass was sent to the department of pathology for imprint cytology and histopathology. The patient had a history of diabetes and hypertension. However, he had no history of fever, weight loss, myasthenia gravis, and the laboratory tests revealed no abnormality. The patient underwent bypass surgery for triple vessel disease and his postoperative follow-ups were uneventful.

The surgically biopsied specimen revealed multiple tissue pieces altogether measuring 2.5 × 2 × 1.8 cm. The tissue pieces were grey-white to grey-brown with some area of calcification.

On imprint cytology, smears showed low cellularity and predominantly comprised of proteinaceous material, a few multinucleated giant cells, and a few lymphoid cells. The possibility of granulomatous pathology was suggested.

Histopathologically, a deposition of homogeneous eosinophilic and hyalinized material around the vessel walls was noted which suggested the possibility of either sclerotic vessels or amyloid deposits. Focal areas showed thymic epithelial cells along with abortive Hassall's corpuscles. Foci of calcification and multinucleated giant cells were also discernible [Figure 1]a, [Figure 1]b, [Figure 1]c. Based on morphology, provisional diagnoses of thymic amyloidoma, or sclerosing thymoma were considered. To differentiate the provisional diagnoses, Congo red staining was done on the representative tissue sections. Congo red stain exhibited congophilia on light microscopy [Figure 1]d and strong apple-green birefringence on a polarized microscope [Figure 2] and [Figure 3]. Immunohistochemistry was negative for both kappa and lambda light chains and serum associated amyloid (SAA). Plasma cell dyscrasia was ruled out due to the absence of M protein spike on serum electrophoresis. Clinically, there was no evidence of systemic amyloidosis. Based on the clinical, histopathological, histochemical, and immunohistochemical evaluation, a final diagnosis of localized thymic amyloidoma was rendered.
Figure 1: (a and b) Histopathology photomicrograph shows nodular masses of amorphous eosinophilic hyaline material surrounding the island of residual thymic tissue. (a) (H and E, ×40), (b) (H and E, ×100), (c) High power view showing extensive hyalinized-collagenous tissue with giant cell reaction. (H and E, ×400), (d) Photomicrograph shows hyaline deposits exhibiting congophilia (Congo red, ×400)

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Figure 2: Photomicrograph shows hyaline deposits exhibiting strong apple-green birefringence showing amyloid deposition (Congo red, polarizing microscopy ×100)

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Figure 3: Photomicrograph on higher magnification, depicting the characteristic apple-green birefringence (Congo red, polarizing microscopy ×400)

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   Discussion Top

Amyloidosis is a family of protein misfolding disorders characterized by extracellular deposition of an insoluble protein that stains with Congo red. The rarity of the localized disease and its nonspecific symptoms causes a delay in diagnosis and thus organ dysfunction. Hence, clinicians and pathologists must consider amyloidosis on their differential aspect for the appropriate tests to be ordered.[9]

Localized amyloidosis usually has a better prognosis than the systemic form.[9] Thereby, determining the local presence of amyloid is of great importance. It is diagnosed based on Congo red-positive area, localized thymic involvement along with no evidence of plasma cell dyscrasia, and systemic amyloidosis.[4] Moreover, subjecting the Congo red positive area to immunohistochemical analysis to determine fibril type (amyloid light chain -AL and amyloid associated -AA) is also required.[5]

Localized thymic amyloidosis is an extremely rare finding with literature showing only six cases being reported till date.[3],[4],[5],[10],[11],[12] The present case is the seventh in the world and the first in India. The average age of the six cases reported so far was 57 years. One of the cases was male,[5] and the other five were females. Two of the cases showed an association with myasthenia gravis.[4],[12] One had a history of rheumatoid arthritis.[10] Two of the cases had a history of hypertension,[3],[5] like our case. Clinical symptoms correlated with the underlying disease in all these cases. One case was an exception of a 55-year-old healthy woman with localized primary thymic amyloidosis who presented with a mediastinal mass, found incidentally on the chest radiograph. This was the first case report on localized primary thymic amyloidosis presenting as an isolated mediastinal mass with no underlying disease.[11] In our case, the patient was having triple vessel disease with underlying diabetes and hypertension. However, the finding of the enlarged thymus was incidental and unrelated to the comorbid conditions. Surgical resection of the mass was the treatment in all cases except in myasthenia gravis where steroid therapy was used in adjunction. Out of the six cases reported till date, immunohistochemical studies revealed positivity for AA type in one case,[10] AL type in three cases indicating positive immunolabeling for kappa and lambda light chains,[4],[5],[11] while the other two were negative for both AL type and AA type similar to our case.[3],[12] Thymic calcifications as seen in our case were a constant finding in all the cases.

Differential diagnostic considerations for an anterior mediastinal mass with extensive hyalinosis and fibrosis include sclerosing mediastinitis, solitary fibrous tumor or lymphoma with prominent sclerosis, sclerosing thymoma, and amyloidoma. Sclerosing mediastinitis is an infiltrative lesion and shows only inflammatory and sclerotic fibro collagenous tissue. Solitary fibrous tumor and lymphoma show proof of their diagnostic entity in the more cellular areas, for example, some areas of an otherwise hypocellular solitary fibrous tumor shows typical pattern-less or storiform spindle-cell morphology. Hodgkin lymphoma with partial sclerosis will show areas with Reed-Sternberg cells. Mediastinal diffuse large cell lymphoma has a characteristic appearance known as compartmentalization, where each tumor cell is surrounded by hyalinized fibrous components. Thymoma can also at times display extensive fibrosis; however, strongly convoluted hyalinized fibrosis is a feature of sclerosing thymoma.[3],[13]

The recently reported case in 2017 by Kato et al.[3] gave a final diagnosis of sclerosing thymoma like thymic amyloidoma. Sclerosing thymoma was a close differential in their study, like our case.

Both sclerosing thymoma and thymic amyloidoma are exceptionally rare disorders.[3] On microscopic examination, sclerosing thymoma displays extensive sclerosis with hyalinization and focal calcification. Scanty thymic tissue is noted. Ancient changes or regressive changes attribute to the pathogenesis of extensive sclerosis and hyalinization in a circumscribed thymoma.[6] Since sclerosing thymoma shows extensive hyalinization of fibrous tissue, sclerosing thymoma and amyloidoma should be considered as possibilities in the differential diagnosis of the lesions in the anterior mediastinum. Both the lesions show giant cell reaction, calcification, and prominent vasculature. Association with myasthenia gravis has also been noted in both the lesions. Complete surgical resection is curative in both entities.[6],[7],[10]

   Conclusion Top

Although thymic amyloidoma is a very rare entity, this case report emphasizes that it should be kept in the differential diagnosis of anterior mediastinal lesions. Congo red staining should always be performed when there is a need to differentiate between sclerosing thymoma and thymic amyloidoma.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Yoon SH, Choi SH, Kang CH, Goo GM. Incidental anterior mediastinal nodular lesions on chest CT in asymptomatic subjects. J Thorac Oncol 2018;13:359-66.  Back to cited text no. 1
Mc Erlean A, Huang J, Zabor EC, Moskowitz CS, Ginsberg MS. Distinguishing benign thymic lesions from early stage thymic malignancies on computed tomography. J Thorac Oncol 2013;8:967-73.  Back to cited text no. 2
Kato Y, Okuda M, Fukuda K, Tanaka N, Yoshizawa A, Saika Y, et al. Sclerosing thymoma-like thymic amyloidoma with nephrotic syndrome: A case report. J Med Case Rep 2017;11:216.  Back to cited text no. 3
Son SM, Lee YM, Kim SW, Lee OJ. Localized thymic amyloidosis presenting with myasthenia gravis: Case report. J Korean Med Sci 2014;29:145-8.  Back to cited text no. 4
Sato F, Hata Y, Otsuka H, Makino T, Koezuka S, Sasamoto S, et al. Isolated nodular thymic amyloidosis associated with diplopia. Ann Thorac Surg 2014;98:1470-2.  Back to cited text no. 5
Bhat A, Selmi C, Naguwa SM, Cheema GS, Gershwin ME. Currents concepts on the immunopathology of amyloidosis. Clin Rev Allergy Immunol 2010;38:97-106.  Back to cited text no. 6
Pepys MB. Amyloidosis. Annu Rev Med 2006;57:223-41.  Back to cited text no. 7
Merlini G, Bellotti V. Molecular mechanisms of amyloidosis. N Engl J Med 2003;349:583-96.  Back to cited text no. 8
Girnius S. Overview of systemic and localized amyloidosis. Rev Health Care 2013;4:231-47.  Back to cited text no. 9
Takamori S, Yano H, Hayashi A, Fukunaga M, Miwa K, Maeshiro K, et al. Amyloid tumor in the anterior mediastinum: Report of a case. Surg Today 2004;34:518-20.  Back to cited text no. 10
Sang Yun H, Jae Jun L, Heejung P, Joungho H, Hong Kwan K, Kyung SL. Localized primary thymic amyloidosis presenting as a mediastinal mass – A case report. Korean J Pathol 2011;45:41–4.  Back to cited text no. 11
Chapman KO, Beneck DM, Dinkin MJ. Ocular myasthenia gravis associated with thymic amyloidosis. J Neuroophthalmol 2016;36:50-2.  Back to cited text no. 12
Chatterjee D, Finch CJ. Sclerosing thymoma. Arch Pathol Lab Med 2015;139:1068-70.  Back to cited text no. 13

Correspondence Address:
Harshi Dhingra
Department of Pathology, Adesh Institute of Medical Sciences and Research, Bathinda - 151 001, Punjab
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_432_19

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