Spinal lymphoma accounts for only 3.3% of all cases of lymphoma of the central nervous system (CNS), which in turn accounts for 1% of all lymphoma (1). Based on our review of the English literature published between 1996 and 2019, only 2 cases of primary T-cell lymphoma of the cauda equina (2, 3) have been reported. Because most of the primary CNS lymphoma (PCNSL) is B-cell lymphoma (4), the imaging characteristics of T-cell lymphoma remain unclear. We report a case of primary T-cell lymphoma at the cauda equina and describe the relevant MRI characteristics.

A 56-year-old female presented with a 3-year history of low back pain. Her medical history was insignificant, with no history of surgery. Her symptoms were insidious and relieved with epidural steroid injections. However, the injection therapy ceased to be effective for 8 months before presentation. She experienced severe radiating pain from the gluteal area to the bilateral posterior thighs and lateral side of the calf, and the first toe, with bilateral leg weakness and fecal incontinence since 4 months before presentation. Although an epidural steroid injection was administered for the radiating pain 1 month before presentation, the pain persisted.

MRI of the lumbar spine was performed to evaluate the refractory back pain. MRI revealed a relatively well-defined, elongated, multinodular intradural lesion of from the L4 body to the S2 body level of approximately 10 cm. The mass had iso-signal intensity to the spinal cord on T1-weigted imaging. Most of the mass revealed iso-signal intensity on T2-weighted imaging; however, few peripheral portions demonstrated high signal intensity similar to the cerebrospinal fluid (CSF). After gadolinium contrast enhancement, the mass showed intense heterogeneous enhancement primarily in the portions of high signal intensity on T2-weighted imaging and along the outer dural wall. The lesion occupied the central spinal canal from the L4 to S2 level completely (Fig. 1A).

Fig. 1
Primary T-cell lymphoma of the cauda equina in a 56-year-old female.
A. An approximately 10-cm-long multinodular mass is located in the cauda equina from the L4 to the S2 body level. On the T1-weighted sagittal image, the lesion is slightly heterogeneous and isointense with the spinal cord. On the T2WI, the lesion is heterogeneously isointense to hyperintense with the spinal cord. On the enhanced fat-suppressed T1WI, the lesion is heterogeneous and shows strong enhancement, particularly along the dural wall. On the T2WI and enhanced fat-suppressed T1-weighted axial images at the L5 vertebral body level, the nodular lesion shows isointensity with heterogeneous enhancement. On the T2WI and enhanced fat-suppressed T1WI at the S1 vertebral body level, the entire spinal canal is tightly packed with the thickened nerve roots, and the peripheral portions of the nerve roots show hyperintensity with bright enhancement.

B. After total laminectomy at the L4/5 level, an abnormal whitish red intradural bulging mass is seen (arrows), which was biopsied.

C. Histopathologic and immunohistochemical examination of the mass on the cauda equina after a biopsy. H&E staining (× 400) shows that the lymphoma cells had infiltrated into the neural tissue with a high nucleus-to-cytoplasm ratio. Immunohistochemistry indicates that most of the atypical large lymphoma cells are positive for CD3 and some are positive for CD20 (× 200).

fs = fat saturated, H&E = hematoxylin and eosin, T1CE = contrast enhanced T1WI, T1WI = T1 weighted image, T2WI = T2 weighted image

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We planned a surgical spinal biopsy. Routine hematology and biochemistry evaluations at admission were normal. The white blood cell count was 11/mm³, and the total protein level was high (105.7 mg/dL; normal range, 8–43 mg/dL) in the CSF study. Fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) PET/CT suggested only a focal, intense hypermetabolic lesion at the spinal canal at the L4-S2 level (maximal standardized uptake value = 6.4). Chest and abdominal contrast-enhanced CT examinations revealed no other abnormality.

Decompressive bilateral laminectomy at L4/5 revealed bulging intradural masses; intradural biopsies were performed subsequently (Fig. 1B). Hematoxylin-eosin staining revealed dense lymphocytic and histiocytic infiltration with granulomatous inflammation along the dural and neural tissues. The repeated epidural injections were considered the cause of granulomatous inflammation. Immunohistochemistry of the tissue was positive for CD3, a marker for T-cell lymphoma in infiltrative lymphocytes, and CD20, a marker for B-cell lymphoma in some cells (Fig. 1C) (5). Multiplex polymerase chain reaction fragment analysis revealed monoclonal T-cell receptor gamma gene rearrangement, indicating a T-cell origin of the lymphoma. Although immunohistochemistry revealed CD20 positivity in some cells, CD20 expression has been reported in peripheral T-cell lymphoma cases (5). The final pathologic diagnosis was primary peripheral T-cell lymphoma basis other examinations including ¹⁸F-FDG PET/CT.

Symptoms including radiating leg pain, leg weakness, numbness, or fecal incontinence resolved gradually after L4/5 decompression. She was treated with intravenous chemotherapy with high-dose methotrexate and high-dose cytarabine for PCNSL every 3 weeks, and the fourth chemotherapy cycle is ongoing currently without major adverse events.

The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki.

PCNSL accounts for only 1%–2% of non-Hodgkin lymphoma. In addition, spinal cord PCNSL is extremely rare (6). Spinal lymphoma accounts for 3.3% of all CNS lymphoma, which constitutes only 1% of all lymphoma (1). To our knowledge, the incidence of primary lymphoma in the cauda equina remains unreported.

Most cases of PCNSL in the cauda equina present with cauda equina syndrome including low back pain, weakness and numbness of the lower limbs, and urinary dysfunction (7).

Primary spinal intramedullary lymphoma usually shows a diffusely enlarged spinal cord on MRI. Most PCNSLs are of B-cell origin, and PCNSLs of T-cell origin are extremely rare (4). The typical MRI features of B-cell lymphoma at cauda equina include isointense or hyperintense enlargement of the cauda equina relative to the spinal cord’s intensity on T1-weighted imaging and hyperintense on T2-weighted imaging. Furthermore, it shows marked enhancement after gadolinium administration (3, 8).

The lesion in our patient was a solid mass lesion with diffuse nerve root thickening. T1-weighted MRI showed isointensity with the spinal cord; T2-weignted imaging showed heterogeneous isointensities and hyperintensities and avid heterogeneous enhancement particularly along the peripheral dural wall.

According to our review of the English literature, only 2 cases of T-cell lymphoma among the primary lymphoma of the cauda equina have been reported, and the reported imaging findings vary among those studies (2, 3). Ooi et al. (2) reported ill-defined intrathecal masses isointense with the CSF on T1-weighted imaging that show significant enhancement on contrast-enhanced T1-weighted imaging; however, they did not report signal intensity on T2-weighted imaging. Morita et al. (3) reported a mass lesion isointense with the CSF on T1-weighted imaging and hypointense on T2-weighted imaging, with homogeneous enhancement after contrast administration. Basis the findings of the 2 previous reports and our case, spinal cord T-cell lymphoma is likely isointense with the CSF on T1-weighted and of variable intensity on T2-weighted imaging with intense contrast enhancement regardless of the homogeneous or inhomogeneous pattern.

The main differential diagnoses of primary tumors arising at the cauda equina include ependymoma, schwannoma, and so forth (9). Myxopapillary ependymomas are the most common tumor in the cauda equina. Myxopapillary ependymoma is known to originate from the glial cells of the filum terminale and accounts for 13% of all spinal cord ependymoma (10). Typically, myxopapillary ependymoma appears as a sausage-shaped mass on the cauda equina with T1 hypointensity, T2 hyperintensity, and intense contrast enhancement (10).

Schwannomas are benign nerve sheath tumors. Schwannoma has traditionally been cited as the most common primary intradural extramedullary spinal tumor; it typically arises from the dorsal spinal nerve root and foraminal extension. Spinal cord schwannoma is rare. On MRI, schwannoma presents as a well-circumscribed T1 hypointense and T2 hyperintense mass with intense contrast enhancement. Large schwannoma lesions may show heterogeneous enhancement (10).

Paragangliomas are also spinal tumors. These are neuroendocrine tumors known to involve the adrenal gland (pheochromocytoma), carotid body (carotid body tumor), jugulotympanic region (glomus jugulare and glomus tympanicum), and vagus nerve (vagal paraganglioma). Spinal paraganglioma is rare and accounts for 3%–4% of cauda equina tumors. Imaging features of paraganglioma include isointensity on T1-weighted imaging, heterogeneous isointensity to hyperintensity on T2-weighted imaging, and intense contrast enhancement. Owing to high vascularity, intratumoral hemorrhage can lead to a salt-and-pepper appearance. The cap sign refers to T2 hypointensity seen along the boundary of the mass and is believed to be hemosiderin deposition (10).

In conclusion, primary T-cell lymphoma of the cauda equina is an extremely rare tumor among non-Hodgkin lymphomas. This case report presents MRI findings of primary T-cell lymphoma of the cauda equina. Differentiating between B-cell lymphoma and T-cell lymphoma in the cauda equina basis MRI findings alone is difficult. Therefore, other studies such as CSF cytology, FDG PET/CT, and ultimately tissue biopsy of the cauda equina are needed for definitive diagnosis.