Role of PET imaging in peritoneal involvement of subcutaneous panniculitis-like T-cell lymphoma

Abstract

Subcutaneous panniculitis-like T-cell lymphoma is a rare subtype of cutaneous T-cell lymphomas and represents less than 1% of non-Hodgkin's lymphomas. Currently, the diagnosis is based on clinical and histological findings although clinical features may be nonspecific. Often, it is localised to subcutaneous tissue without lymph node involvement. The literature is sparse but unusual presentations have been described to involve mesentery, breast and even eyelids. Fluorine-18 fluorodeoxyglucose positron-emission tomography/computed tomography has been reported to be useful in assessing disease activity, extent and treatment response in subcutaneous panniculitis-like T-cell lymphoma but we find that it can also be a diagnostic aid for atypical presentations. In our case report, we describe a patient who presented with a neck lump but did not have any other obvious cutaneous lesions. This was biopsied and had histological features in keeping with subcutaneous panniculitis-like T-cell lymphoma. Due to the atypical presentation, positron-emission tomography was crucial for detecting the extracutaneous and likely primary site of disease in the peritoneum, which hence guided the subsequent biopsy to this affected area and confirmed the diagnosis.

Keywords: PET/CT; Subcutaneous panniculitis-like T-cell lymphoma; anterior abdominal omentum; computed tomography; peritoneum; positron-emission tomography; primary cutaneous lymphoma.

Figure 1. A 30-year-old gentleman with SPTCL presenting initially with a subcutaneous nodule at the left neck. Histology of this nodule is as described below

Findings: Hematoxylin and eosin (H&E) stain (magnification 5x) demonstrates fibroadipose tissue which shows a panniculitis-like lymphocytic infiltrate (Figure 1A). On higher magnification (40x), intermediate-sized atypical lymphocytes with irregular nuclei are seen to rim adipocytes (Figure 1B). The lymphoproliferation comprises a CD3-positive T-cell population (Figure 1C). The T-lymphoproliferation shows a cytotoxic phenotype, with diffuse expression of Granzyme B (Figure 1D). Overall, these findings are compatible with SPTCL.

Figure 2. A 30-year-old gentleman with SPTCL involving various sites with the primary disease in the anterior abdominal omentum. Whole-body positron emission tomography/computed tomography

FINDINGS: A whole-body positron emission tomography/computed tomography (PET/CT) reveals an ill-defined FDG avid subcutaneous fat-stranding which is seen posterior to the left sternocleidomastoid muscle (SUVmax 5.2, Figure 2A, white arrow). This represents disease involvement and likely the site of prior biopsy. FDG avid focal fat stranding is also noted at the cardiophrenic region (SUVmax 8.9, Figure 2B, white arrow). FDG avid areas of fat stranding in the omentum in the anterior abdomen (SUVmax 11.9, Figure 2C, white arrow). Whole body PET MIP image provides an overview of these abovementioned sites of disease involvement (Figure 2D). The FDG avid areas of fat stranding in the anterior abdominal omentum/peritoneum extends from the left hyponchrondrium to the left lumbar region (Figures 2E, 2F and 2G, white arrows). TECHNIQUE: PET/CT imaging was performed from the vertex of the skull to the feet at 75 minutes after IV administration of 13.0 mCi of F-18 Fluorodeoxyglucose (FDG). Enhanced CT was performed for the purpose of attenuation correction and anatomical localization. 130ml of Omnipaque 350 was administered. Slice thickness: 3.75 mm.

Figure 3. A 30-year-old gentleman with SPTCL, on a follow-up scan post initial, first round of chemotherapy regime. Contrast-enhanced computed tomography of the abdomen/pelvis

FINDINGS: Interval increase of the large area of fat stranding of the anterior omentum bilaterally (Figure 3C, white arrow) and slightly more on the left (Figure 3B, white arrow) with increasing soft tissue density interspersed with fat, when compared to Figures 2F and 2G, representing disease progression. Area of focal fat stranding also again seen in the left hypochondrium (Figure 3A). TECHNIQUE: A total of 80ml of Ultravist 370 was administered. Contrast-enhanced axial images in the soft tissue window, on portal venous phase.

Figure 4. A 30-year-old-gentleman with SPTCL having refractory disease on the follow-up scan despite changing to a new, second round of chemotherapy regime. Contrast-enhanced computed tomography of the abdomen/pelvis

FINDINGS: The focal nodular fat-stranding in the upper left hypochondrium is more prominent and extensive (Figure 4A, black arrow) when compared to Figures 2E and 3A. Interval increase in extent of focal nodular fat-stranding along transverse mesocolon, more extensive and measuring up to 4.7 cm in maximal thickness (Figure 4B, white arrow). Interval increased focal nodular fat-stranding in the right hypochondrium around hepatic flexure region, measuring up to 2.4 cm in thickness (Figure 4C, white arrows), when compared to Figure 3C. TECHNIQUE: A total of 80ml of Omnipaque 350 was administered. Contrast-enhanced axial images in the soft tissue window, on portal venous phase.

Figure 5. A 30-year-old gentleman with SPTCL where the primary disease is seen in the anterior abdominal omentum. Histology from the open biopsy of the anterior abdomen omentum is as described below

Findings: H&E stain (magnification 5x) demonstrates panniculitis-like infiltrate of omental fat (Figure 5A). On higher magnification (20x), atypical lymphocytes are seen rimming adipocytes and in the interstitium (Figure 5B). The lymphomatous population retains its cytotoxic phenotype with positivity for Granzyme B (Figure 5C) as well as expression of T-cell hemireceptor (TChR)-beta F1 (Figure 5D). These findings are in keeping with involvement of refractory SPTCL.