AJR 2004; 182:514
© American Roentgen Ray Society
Radiologic-Pathologic Conferences of Massachusetts General
Hospital |
FDG PET of Rosai-Dorfman Disease of the Thymus
Ruth Lim1,
Conrad Wittram1,
Judith A. Ferry2 and
Jo-Anne O. Shepard1
1 Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston,
MA 02114.
2 Department of Pathology, Massachusetts General Hospital, Boston, MA
02114.
Received August 12, 2002;
accepted after revision March 31, 2003.
Address correspondence to C. Wittram.
A43-year-old man presented with a chief complaint of a left neck mass. Neck
CT revealed a 2-cm anterior mediastinal mass. The patient was then referred to
our institution for a thoracic surgery consultation. Physical examination was
unremarkable and revealed no palpable neck mass. CT of the thorax showed an
anterior mediastinal mass (Fig.
1A); no additional abnormalities were identified. FDG positron
emission tomography (PET) was performed on an Ecat EXACT HR+ PET scanner
(Siemens Medical Systems, Malvern, PA; CTI, Knoxville, TN) plus PET camera
(CPS Innovations, Knoxville, TN) 45 min after IV injection of 15.6 mCi (577.2
MBq) of FDG. This study revealed a focus of intensely increased glycolytic
activity in the anterior mediastinum, corresponding in position to the CT
abnormality (Fig. 1B). The
patient underwent successful mediastinoscopy and resection of this anterior
mediastinal mass, with a working diagnosis of thymoma.
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Fig. 1A. —43-year-old man with Rosai-Dorfman disease of thymus.
Contrast-enhanced CT scan shows well-defined prevascular anterior mediastinal
mass, which measures 2.5 x 1.6 cm in axial plane dimensions.
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Fig. 1B. —43-year-old man with Rosai-Dorfman disease of thymus. Axial
FDG positron emission tomography image reveals focus of abnormally increased
glycolytic activity corresponding in location to anterior mediastinal mass
seen on CT.
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Pathologic examination showed a diffuse proliferation of large histiocytic
cells forming a discrete mass surrounded by thymic tissue showing fatty
involution. Scattered lymphoid follicles, small aggregates of plasma cells,
and a few clusters of foamy macrophages were also identified (Figs.
1C and
1D). The cytologic features did
not suggest a histiocytic malignancy. Immunohistochemical studies showed that
the large distinctive histiocytes were positive for S-100 protein and faintly
positive for CD30 and CD68. They were negative for cytokeratin, CD1a, MART-1
antigen, and melan-A antibody (A103). The histologic features were diagnostic
for Rosai-Dorfman disease, and the results of the immunohistochemical studies
supported this diagnosis.
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Fig. 1C. —43-year-old man with Rosai-Dorfman disease of thymus.
Medium-power photomicrograph shows thymic mass consisting of proliferation of
histiocytes with scattered reactive lymphoid follicles with germinal centers.
(H and E, x16)
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Fig. 1D. —43-year-old man with Rosai-Dorfman disease of thymus.
High-power photomicrograph reveals distinctive histiocytes of Rosai-Dorfman
disease that are large with abundant finely granular pink cytoplasm and
relatively large nuclei with open chromatin and distinct nucleoli. Few
histiocytes show emperipolesis of lymphocytes, with intact lymphocytes
(arrow) present in their cytoplasm. (H and E, x250)
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First described in 1969, Rosai-Dorfman disease is a rare condition of an
unknown cause. More than 600 cases have been reported worldwide. All age
groups and both sexes are affected, but it is more common in children and
adolescents and in males. The disease is characterized by massive, painless,
bilateral cervical lymphadenopathy in 90% of patients and may be accompanied
by low-grade fever. Other common sites of nodal involvement include the
axillary, inguinal, paraaortic, and mediastinal regions. Symptoms are also
related to the presence and distribution of extranodal disease, which occurs
in approximately 43% of cases, with or without lymph node involvement. Common
extranodal sites include the skin, central nervous system, bone, soft tissues,
upper respiratory tract, and salivary glands. The clinical course of
Rosai-Dorfman disease is usually indolent and self-limited, with gradual
subsidence of symptoms over months to years. However, chronic disease can
occur with patterns of stability, slow progression, exacerbation, or
spontaneous remission. In rare instances, Rosai-Dorfman disease can take on a
more aggressive, potentially fatal form, with destruction of osseous,
cartilaginous, and soft-tissue structures. There is no consensus on the
treatment of unremitting Rosai-Dorfman disease. Surgery for localized disease,
particularly in the head and neck, must be considered carefully because of the
risk of significant function loss. No strong evidence supports the use of
radiation or chemotherapy for either localized or more widespread aggressive
disease [1].
In the previously reported case of thymic involvement by Rosai-Dorfman
disease, the patient presented with extensive cervical, axillary, and inguinal
lymphadenopathy [2]. To our
knowledge, no previous incidents of the disease isolated to the thymus have
been reported. Our patient initially presented with a chief complaint of a
neck mass, although subsequent physical examination, and CT results were
negative for such a finding. One could speculate that cervical lymphadenopathy
may have been present initially and spontaneously remitted before the patient
underwent evaluation at our institution.
A solitary focus of increased activity in the thymus on an FDG PET scan can
be observed in a number of benign and malignant thymic conditions, including
hyperplasia, rebound after chemo- or radiotherapy, and thymoma
[3]. However, in this case of
Rosai-Dorfman disease, the thymic mass was composed of histiocytes, not thymic
cells. Kubota et al. [4]
described in 1992 that macrophages (histiocytes) adjacent to a tumor show
higher FDG uptake than viable tumor cells. This finding supports our
observation of intensely increased FDG uptake by a histiocytic proliferative
disorder. Distinguishing Rosai-Dorfman disease from malignant lesions may be
difficult to establish on FDG PET in light of the observation that
proliferative histiocytes may have higher FDG uptake than tumor cells.
References
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