Rosai–Dorfman Disease with Nodal and Rare Extranodal-thymic and Pancreatic Involvement Documented with 18F-FDG-PET/CT

An 18-year-old male initially presented with bilateral neck swelling associated with odynophagia and dysphagia, low-grade fever, and weight loss. Ultrasonography (USG) neck revealed multiple enlarged solid hypoechoic nodes with loss of fatty hilum in bilateral levels IB, II, III, IV, and V and left level VI, the largest measuring 3.8 cm × 2.9 cm in right level V. USG (abdomen and pelvis) showed multiple enlarged periportal, retroperitoneal, and mesenteric nodes, the largest measuring 3.1 cm × 2.7 cm in the periportal region. Left cervical lymph node excision biopsy revealed a lymph node with a thickened capsule. Lymph node parenchyma showed dilated sinuses with atypical histiocytes showing foamy to eosinophilic cytoplasm. On immunohistochemistry, the atypical cells were positive for S100p and CD163, whereas negative for CD1a, AE/AE3, P40, and EMA and were suggestive of Rosai–Dorfman disease (RDD). Computed tomography (CT) Neck (P + C): showed massive cervical, mediastinal lymphadenopathy and enlarged thymus. He was referred for 18-fluorine-fluorodeoxyglucose-positron emission tomography/CT (18F FDG PET/CT) for disease status evaluation. 5.5 mCi ¹⁸F-FDG was injected intravenously, and the scan was acquired 60 min postinjection on Philips TOF PET/ CT (slice thickness of 2.5 mm, soft -tissue reconstruction kernel of 120 keV, and 50 mAs). ¹⁸F-FDG-PET/CT images [Figures 1,2,3 and 4]-[A, C, E, G and I] showed FDG-avid discrete and conglomerated lymph node mass involving the bilateral cervical I, II, III, IV, V, VI, preauricular supraclavicular lymph nodes, mediastinal and abdominal lymph nodes, few reference nodes mentioned below: Conglomerated right cervical II lymph node mass measuring 4 cm × 2.7 cm × 4.3 cm (SUV_max 7.67) (red arrow), prevascular node, conglomerated splenic node, measuring 3.1 cm × 2.1 cm × 1.7 cm (SUV_max 8.20), FDG avid enlarged thymus seen, SUVmax11.5 measuring 8 cm × 6.5 cm (green arrow), FDG avid hypodense lesions in head, body, and tail of pancreas with dilatation of main pancreatic duct – head of the pancreas, measuring 2.5 cm × 3.2 cm × 3.3 cm (SUV_max 12.09) (blue arrow). The patient was started on chemotherapy, on Tab 6-mercaptopurine (6-MP) daily, and methotrexate (MTX). One year later, he was referred for an ¹⁸F-FDG-PET/CT scan response evaluation. The images [Figure 1, 2, 3 and 4 - B, D, F, H and J] show reference lesions for response evaluation, which demonstrated FDG-avid conglomerated bilateral cervical lymph nodes measuring 4.2 cm × 2.5 cm × 7.1 cm (SUV_max: 7.11.) (red arrow), prevascular node and an FDG-avid enlarged thymus seen measuring 8.0 cm × 3.4 cm (SUV_max: 7.58) (green arrow), FDG avid uptake noted in the pancreas (head measuring 2.4 cm × 3.4 cm [SUV^max: 8.59] [blue arrow], body measuring 1.7 cm × 3.2 cm [SUV_max: 8.17], and tail 3.3 cm × 2.8 cm [SUV_max: 13.12]). Overall scan findings were suggestive of stable disease status.

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Figure 1:

MIP images of 18F-FGD PET/CT done at A) Baseline and B) Response evaluation aft er 1 year. Red arrow- conglomerated and discrete cervical lymph nodes, green arrow- Enlarged thymus, blue arrow- Head of pancreas

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Figure 2:

Axial images- 1st row: 18F-FDG PET/CT, 2nd row: CT image and 3rd row: corresponding MIP images of conglomerated and discrete cervical lymph nodes (red arrow) at C) Baseline and D) Response evaluation, and enlarged thymus (green arrow) at E) Baseline and F) Response evaluation.

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Figure 3:

Axial images- 1st row: 18F-FDG PET/CT, 2nd row: CT image and 3rd row: corresponding MIP images of head of pancreas (blue arrow) at G) Baseline and H) Response evaluation.

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Figure 4:

Sagittal images- 1^st row: ¹⁸F-FDG PET/CT, ^2nd row: CT image and ^3rdrow: corresponding MIP images of enlarged thymus (green arrow) and head of pancreas (blue arrow) at I) Baseline and J) Response evaluation.

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RDD is a rare non-Langerhans cell histiocytosis.^[1] Two different clinical types of RDD exist: a nodal and an extranodal variant that manifests as lymphadenopathy and may also include organ and systemic symptoms. The nonspecific imaging features of RDD can make radiologic diagnosis challenging. The extranodal form may involve the gastrointestinal tract, skin, subcutaneous tissue, and respiratory tract.^[2] Reports of RDD in the thymus were significantly rare.^[3-5] Rarely does RDD occur in the gastrointestinal tract, particularly in the liver and pancreas.^[6,7] Given that spontaneous remission occurs in 20%–50% of patients with nodal/ cutaneous illness, monitoring is frequently appropriate following an RDD diagnosis.^[8] patients with simple lymphadenopathy or asymptomatic cutaneous disease may benefit from this approach.^[8] Steroids help lessen lymph node size and symptoms.^[9] Response has also been reported with a combination of low-dose MTX and 6-MP.^[10] RDD lesions, particularly involving extranodal regions, are known to be FDG-avid.^[11] Some investigators use FDG-PET/CT for initial staging when it is feasible.^[12] Due to FDG avidity, particularly in extranodal sites, few studies have highlighted the utility of FDG PET/CT in initial evaluation and treatment monitoring.^[7,11,12] Our case showed RDD with nodal and extranodal-thymic and pancreatic involvement, which is very rare. The initial 18F-FDG PET/CT scan showed widespread disease involvement, with the follow-up scan 1 year later showing stable disease status with no new lesion.