History
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.
Findings
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.
Discussion
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 SUVmax 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 SUVmax 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 SUVmax levels.
Intense accumulation of 18F FDG in the lower spinal cord from T12-L4, as well as the spinal nerve roots seen in the present case are typical of spinal cord DLBCL. The enlargement of the involved nerve roots seen on both CT and PET correlates with typical MRI findings in similar clinical situations. The large, intensely hypermetabolic mass in the right psoas region, which arises from the involved right L2 spinal nerve root may be an affected paravertebral ganglion. In the absence of any non-nervous system involvement, the right psoas mass was evaluated as the primary neurological origin, and the biopsy revealed it to be a primary CNS large B-cell lymphoma.Conclusion
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.
Examination protocol
Scanner: Biograph Vision 450
