Burkitt’s Lymphoma Presenting as Peritoneal Super Scan on 18F-FDG PET/CT

INTRODUCTION

Burkitt’s lymphoma is a highly aggressive subtype of B-cell non-Hodgkin lymphoma (NHL), accounting for a minor fraction of all NHLs.^[1] It exhibits a bimodal age distribution, with peak incidences in late childhood and mid-adulthood.^[2] Immunosuppression, particularly HIV infection, is a strong risk factor for adult Burkitt’s lymphoma.^[3] Histologically, it is characterized by a monomorphic population of intermediate-sized mature lymphocytes with spherical nuclei, lacy chromatin, small nucleoli, and basophilic cytoplasm containing prominent vacuoles. Morphologic variants include pleomorphic and plasmacytoid forms.^[4] A high mitotic index reflects its rapid proliferative activity, and increased apoptosis leads to the classic “starry sky” appearance caused by tingible-body macrophages that engulf apoptotic debris.^[5] This pattern is also associated with Epstein–Barr virus infection, particularly in endemic cases.^[6] Although extranodal involvement is seen in up to 40% of NHL cases, peritoneal involvement remains unusual and is often mistaken for peritoneal carcinomatosis or tuberculosis (TB) on imaging.^[7-9] Burkitt’s lymphoma with peritoneal lymphomatosis (PL) is exceedingly rare with most available data limited to isolated case reports.^[7,8,10] In such cases, PL may mimic other peritoneal pathologies both clinically and radiologically, leading to diagnostic challenges.^[11,12]

In nuclear medicine, the term “super scan” originally described a bone scintigraphy pattern in which there is intense, diffuse radiotracer uptake throughout the skeleton with suppressed physiological activity in nonskeletal tissues, commonly seen in extensive osteoblastic metastases or metabolic bone diseases.^[13] A similar imaging pattern, termed the “peritoneal super scan,” has been described in fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT), characterized by diffuse peritoneal FDG uptake and reduced physiological distribution elsewhere, including the brain and kidneys.^[14]

Here, we provide a description of two pediatric cases of Burkitt’s lymphoma presenting as peritoneal super scans on 18F-FDG PET-CT.

CASE REPORTS

Case 1

An 8-year-old female child presented with complaints of loss of appetite and loss of weight (~5% of total body weight) for 1 month. The patient had abdominal distention and a large palpable mass in the abdomen on physical examination. Her biochemical tests showed raised alkaline phosphatase-369 IU/L, (46–116) CA125 63.5 U/mL (<30), and lactate dehydrogenase 836 (120–246 U/L) levels. Her contrast-enhanced CT (CECT) abdomen revealed a large heterogeneously enhancing soft-tissue density mass with internal areas of necrosis in the retroperitoneal region reaching into the pelvic cavity. She was referred for FDG PET-CT for further characterization and staging, which revealed a large FDG avid abdomino-retroperitoneal mass (11.8 cm × 11.7 cm × 26.6 cm, AP × TR × CC (Anteroposterior x Transverse x Craniocaudal), SUVmax 12.9). Multiple other intensely metabolically active enlarged discrete and coalescent lymph nodes on both sides of the diaphragm with multiple metabolically active deposits in the greater omentum and serosal aspects of splenic surface and bowel loops were present. FDG avid diffuse thickening of parietal peritoneum with bilateral mild pleural effusion and abdominopelvic ascites with generalized reduction in physiological FDG uptake in the brain parenchyma and bilateral kidneys were noted [Fig. 1a] while interim maximum intensity projection image (MIP) showed restoration of physiological brain and urinary FDG uptake with symmetrical brown fat activity in bilateral cervical and thoracic paravertebral regions [Fig. 1b]. Baseline axial PET/CT images revealed FDG-avid parietal peritoneal thickening [Fig. 1c], which resolved on interim imaging [Fig. 1d]. Enlarged FDG-avid retroperitoneal, upper abdominal, and pelvic nodes/nodal mass were noted at baseline [Fig. 1e, g, i] with complete resolution on interim images [Fig. 1 f, h, j]. Ultrasound-guided biopsy [Fig. 2] from the retroperitoneal mass revealed fibrocollagenous soft-tissue core infiltrated by intermediate-sized atypical cells arranged in sheets with clumped chromatin and scant cytoplasm [Fig 2a]. On immunohistochemistry, the tumor cells were immunopositive for CD20 [Fig 2b], CD 79a, c-myc [Fig 2c], BCL-6, and negative for CD3, Tdt, and BCL-2. The diagnosis of Burkitt’s lymphoma was made.

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Fig 1:

(a-j) MIP images at baseline (a) demonstrate diffuse peritoneal hypermetabolism with loss of physiological brain uptake (orange arrow). (b) Interim MIP shows restoration of physiological brain and urinary FDG uptake, with symmetrical intense brown fat uptake in bilateral cervical (yellow arrow) and thoracic paravertebral regions (black arrow). (c) Fused axial PET/CT images demonstrate FDG-avid parietal peritoneal thickening at baseline with (d) resolution on interim scan. (e, g, i) Enlarged FDG-avid retroperitoneal, upper abdominal, and pelvic nodes/nodal mass (green arrow in e and g) are figFDG: Fluorodeoxyglucose, PET/CT: Positron Emission Tomography/Computed Tomography]

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Fig 2:

(a) Biopsy sample of case 1 - sheets of intermediate-size atypical lymphoid cells with hyperchromatic nuclei and scant cytoplasm on Hematoxylin and Eosin stain on 40x magnification, (b) diffuse immunopositivity to CD20 on 20x magnification and (c) c-myc positivity of approximately 70% on 20x magnification

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The patient was referred to medical oncology, where she received 2 cycles of BFM chemotherapy with rituximab over the next 2 months. On interim PET-CT, the patient achieved complete metabolic resolution with a reduction in the size and metabolic resolution of retroperitoneal nodal mass and complete resolution of the other FDG avid lesions (Deauville score 1). The brain parenchyma now showed normal physiological uptake in the brain. The biochemical parameters went back to normal. Clinically, the patient improved and did not have any major side effects till the documentation of this report.

DISCUSSION

PL, which is more commonly associated with aggressive NHLs such as diffuse large B-cell lymphoma, can occasionally be seen in Burkitt’s lymphoma, an uncommon NHL histological subtype (diffuse large B cell lymphoma).^[1,7-9,15]

The mechanism of peritoneal spread remains unclear, particularly because the omentum lacks native lymphoid tissue. Proposed pathways include direct extension through the transverse mesocolon, greater omentum, and visceral peritoneal surfaces.^[8,16]

Although traditional anatomical imaging can detect peritoneal involvement, it often cannot distinguish lymphomatosis from carcinomatosis, TB, or mesothelioma,^[16] both of which may present with overlapping symptoms such as abdominal pain, low-grade fever, and weight loss, posing a diagnostic challenge.^[10,11,16] FDG PET-CT has been proven useful in distinguishing lymphomatous involvement from other etiologies due to their ability to assess metabolic activity.^[3,12]

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Fig 3:

(a-j) MIP image (a) showing diffuse peritoneal and pleural hypermetabolism and severe reduction in physiological brain metabolism (orange arrow), (b) fused PET-CT Coronal and axial images (c, d, e and f) and CECT axial images (g, h, i and j). Diffuse FDG avid bilateral pleural (yellow arrow in c) and pericardial (green arrow in c) thickening with large volume bilateral pleural and pericardial effusion (c, d), diffuse FDG avid thickening of parietal peritoneum (grey arrows in d and f) in abdomen and pelvis, greater omentum (blue arrow in e) and small bowel mesentery (violet arrow in e) with edematous bowel wall thickening (e-j). [MIP: Maximum Intensity Projection, FDG: Fluorodeoxyglucose, PET/CT: Positron Emission Tomography/Computed Tomography, CECT: Contrast-Enhanced Computed Tomography]

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On FDG PET-CT, intense uptake in the peritoneum and omentum can obscure physiological tracer distribution in organs such as the brain, kidneys, and soft tissues, producing a pattern referred to as a “peritoneal superscan” – a term adapted from bone scintigraphy, where a superscan is characterized by high skeletal-to-soft tissue uptake and absent renal visualization.^[13] This imaging pattern may be attributed to the tumor sink effect, in which a large tumor burden sequesters radiotracer, reducing availability for normal physiological uptake elsewhere.^[14,17] While well documented in prostate-specific membrane antigen PET imaging,^[18] this effect is increasingly recognized in FDG PET-CT, particularly in high-grade lymphomas.^[19,20]

In our second case report, CECT suggested a differential diagnosis of peritoneal TB versus lymphoma. However, 18F-FDG PET-CT revealed a characteristic peritoneal superscan pattern with extensive involvement, active lymphadenopathy above and below the diaphragm, and focal bone marrow uptake in the right scapula, favoring a lymphomatous etiology, which was confirmed by histopathology.

CONCLUSION

PL is a very unusual presentation of NHLs and is even rarer with Burkitt’s lymphoma. Imagiologists should keep a high index of suspicion for high-grade NHLs when a “peritoneal super scan” is seen on 18F-FDG PET-CT. FDG PET-CT can successfully stage and help in the treatment response evaluation of such cases. It can also potentially help in differentiating PL from TB, the great masquerader.