¹⁸F FDG PET/CT delineation of diffuse large B-cell lymphoma involving lower spinal cord and spinal nerve roots

By Partha Ghosh, MD, Siemens Healthineers, Hoffman Estates, IL, USA
Data and images courtesy of Osaka City University Hospital, Osaka, Japan

A 50-year-old female with progressive weakness in both legs underwent PET/CT imaging to evaluate a spinal pathology. The study was conducted on a Biograph Vision™ 450 scanner using Fludeoxyglucose F 18 (¹⁸F FDG) Injection.

Approximately 51 minutes following the intravenous (IV) injection of 4.6 mCi (173 MBq) of ¹⁸F FDG and completion of the initial low-dose CT, a dynamic whole-body PET acquisition was performed with FlowMotion™ continuous-bed-motion technology.

A total of 6 consecutive whole-body passes were acquired at 3 minutes and 19 seconds per pass and subsequently summed into a single PET dataset. The individual dynamic whole-body PET acquisitions, as well as the summed PET data, were evaluated on a syngo^®.via workstation.

The visual evaluation of the sequential dynamic whole-body PET acquisitions, as well as the summed PET image comprised of data acquired over 20 minutes, shows intense ¹⁸F FDG uptake in the lower spinal cord, lumbar spinal nerve roots, and cauda equina. In addition, a linear mass in the region of right psoas muscle, which includes the sacral spinal nerve roots within the pelvis is evident.

As depicted in Figures 4-9, the ¹⁸F FDG PET/CT shows hypermetabolic and enlarged lower spinal cord and spinal nerve roots in bilateral L1 and L2, L4 and L5, and S1 and S2. The large right psoas mass appears to be an enlarged extension of the hypermetabolic right L2 nerve root. The right sacral nerve roots also show an extension of hypermetabolism along the neural sheath.

The pattern of such hypermetabolism—including the involvement of the spinal cord with continuous extension into spinal nerve roots seen in the lower spinal cord and L1 and L2 spinal nerve roots, as well as discontinuous involvement of right L4-L5 and S1 and S2 nerve roots with extension along nerve tracts—suggests a primary spinal cord lesion with diffuse extension along nerve sheaths, which indicates the possibility of a primary spinal cord lymphoma or leukemia.

The patient underwent resection of the psoas lesion and a biopsy was performed on a surgical specimen of the involved nerve roots. The histopathology report revealed diffuse large B-cell lymphoma (DLBCL), and the patient was diagnosed with primary central nervous system DLBCL derived from the lumbar spinal cord.

Primary central nervous system B-cell lymphoma accounts for 4-6% of all malignant lymphomas.¹ There is increased incidence in immuno­compromised individuals, including acquired immunodeficiency syndrome and transplant recipients. Direct infiltration of the cauda equina is rare and is usually in the form of a primary localized or disseminated form of central nervous system (CNS) lymphoma. Most common presenta­tions are muscular weakness, parapa­resis or paraplegia, and radiculopathy. Magnetic resonance imaging (MRI) findings include swelling of the in­volved spinal cord and nerve roots, which is either hypo- or iso-intense to the normal spinal cord in both T1 and T2 with enhancement following contrast. ¹⁸F FDG PET/CT shows in­creased tracer accumulation in the involved areas with the SUV being lower than that of general DLBCL. In a case report of lower spinal cord and cauda equina DLCBL, the calculated SUV_max in two lesions at 9.6 and 4.9 were deemed lower than those reported for non-neurological DLBCL.¹ In this particular case, the SUV_max were much higher, although consideration should be given to the Biograph Vision 450 PET/CT system and its 214 picosecond time-of-flight (ToF) performance with high-resolu­tion PET acquisition, which results in higher SUV_max levels.

This case illustrates how a compre­hensive PET/CT evaluation of nervous system lymphoma helps delineate the extent of disease infiltration. The high resolution of the Biograph Vision 450 system paired with the high contrast-to-background ratio achieved due to high ToF perfor­mance helps achieve sharp definition with high contrast within nerve tract lesions, as seen in the involved pelvic nerves arising from the S1 and S2 nerve roots that are clearly defined on PET/CT.