Primary CNS lymphoma is a very low incidence non-Hodgkin’s lymphoma, accounting for approximately 2% of all primary intracranial tumors, which usually originate in the paraventricular white matter of the brain, and even more rarely appear outside the axis.
Recently, Ang et al. from the University of Edinburgh co-reported such an extremely rare case of CNS lymphoma, presenting with even more elusive symptoms. In this article, we describe in detail the features of this case and the complete clinical diagnosis.
Basic information of the case
The patient is a 55-year-old male who complained of severe paroxysmal right hypoglossal discharge-like pain for 6 months, starting in the upper lip and cheek and progressing to numbness in the chin. The site of pain was similar to the area of distribution of the mandibular branch of the trigeminal nerve, but physiological examination suggested no obvious signs of nerve injury except for hyperalgesia in the chin.
The remaining medical history included coronary artery disease, hypercholesterolemia, and depression, all of which were managed with medications. There was no history of genetic disorders or epidemics.
Initial diagnosis and treatment
The patient was initially diagnosed with trigeminal neuralgia.
He underwent microvascular decompression after taking pregabalin and gabapentin without success.
Radiological findings
MRI of the head showed a malignant hyperplastic mass in the right extra-axial pterygoid wing, invading the right trigeminal nerve pool segment, with a maximum size of 40 mm × 20 mm × 25 mm, and a distinct dural caudal sign. The mass extended laterally along the middle cranial fossa for approximately 10 mm (Figure 1), through the significantly dilated right foramen ovale (approximately 7 mm in diameter) toward the infratemporal fossa, and slightly toward the right infraorbital foramen and foramen ovale.
1. The mass exhibits a short T1 signal in the cross-sectional (A), coronal (B), and sagittal (C) views
The image shows a marked narrowing of the right Meckel’s lumen and a partial narrowing of the right cavernous sinus. The lesion is adjacent to the right internal carotid artery, but there is no obvious sign of compression.
The patient’s left trigeminal nerve passes normally through the Meckel’s cavity (red arrow); the patient’s right trigeminal nerve is obscured by the mass and the Meckel’s cavity almost disappears.
Based on the above anatomical localization and imaging features, the doctor considered that the mass was most likely a nerve sheath tumor or meningioma and gave conservative treatment. Unexpectedly, however, the patient developed progressive pain within 8 weeks.
Tumor recurrence and surgery
MRI review showed an enlarged tumor with enhanced subcortical white matter T2 signal, suggesting soft meningeal infiltration. The patient then underwent right trigeminal nerve mandibular branch block and right temporal osteotomy.
Due to intraoperative pathology difficulties and the risk of destruction of the cavernous sinus, only a partial resection of the right pterygoid pterygoid tumor was performed, preserving the cavernous sinus portion.
After surgery, the patient’s facial pain was greatly relieved, lactate dehydrogenase level was normal, human immunodeficiency virus test was negative, scrotal ultrasound and whole-body CT scan did not reveal any tumor metastases, and cerebrospinal fluid and bone marrow examination did not reveal abnormal cells and soft meningeal infiltration.
Final diagnosis and treatment
Postoperative histopathological examination showed that the tumor contained medium to large B lymphocytes with multiple morphologies and lobulated nuclei (CD20-positive). The patient was finally diagnosed with primary central diffuse large B-cell lymphoma.
The patient was first treated with high-dose methotrexate and rituximab and local radiotherapy to the tumor area, and was treated with R-CHOP chemotherapy after control of disease and pain.
Case Analysis and Summary
Clinically, the vast majority of paroxysmal pain in the trigeminal nerve is caused by nerve root compression or demyelination; only 10% of patients may be associated with a tumor, and the associated skull base tumors are usually only nerve sheath tumors and meningiomas.
In previous reports, only one case of malignant lymphoma originated in the pterygoid wing, while the rest originated elsewhere; one case of lymphoma causing trigeminal neuralgia originated in the Meckel’s cavity. All of these lesions, like the case in this article, are often misdiagnosed as nerve sheath tumors or meningiomas.
The extremely rare case of CNS lymphoma in this article, however, presented a paradoxical localization (primary in the pterygoid wing) and symptoms similar to other common diseases (trigeminal neuralgia), making its diagnosis extremely challenging.
However, a previous study with a small sample confirmed that bone tissue hyperplasia without a bone hypertrophic response and cavernous sinus infiltration without carotid stenosis are beneficial in differentiating lymphoma from meningioma, which usually presents with bone hypertrophy and bone metastasis of the tumor as well as carotid lumen stenosis.
It is hoped that the findings of this study and the cases reported here will bring some clinical experience and help in the management of rare lymphomas.