Magnetic Resonance Spectroscopy in the Evaluation of Biopsy-Indeterminate Primary Central Nervous System Lymphoma: A Case Report.

Primary central nervous system lymphoma (PCNSL) is a rare, aggressive extra-nodal non-Hodgkin lymphoma restricted to the central nervous system without systemic involvement at diagnosis. PCNSL can present with a wide array of symptoms, including cognitive dysfunction, focal neurologic deficits, or seizures. This case report utilizes a chart review of the history, physical examination, laboratory tests, imaging findings, and pathology reports recorded during this patient's hospital encounters. We present the case of a middle-aged woman with a past medical history of traumatic brain injury and seizures with incidental neuroimaging findings on head computed tomography showing right parietal lobe and subcortical edema. She reported subacute onset of diffuse paresthesia, generalized weakness, severe migraine headaches, poor balance, and falls. She was admitted to the hospital for further evaluation of her neurological symptoms and was started on prophylactic dexamethasone. Magnetic resonance imaging (MRI) demonstrated avidly enhancing lesions in the bilateral cingulate gyri and periventricular regions, right frontoparietal region, right temporal lobe, corpus callosum, hypothalamus, and basal ganglia, with vasogenic edema and midline shift. Magnetic resonance spectroscopy (MRS) yielded an elevated choline-to-creatinine ratio, decreased N-acetylaspartate peak, normal myoinositol, and a prominent lipid peak - findings consistent with PCNSL. Steroids were continued after discharge to treat cerebral edema, and a stereotactic biopsy performed 28 days later was non-diagnostic. Subsequent brain MRI showed marked disease regression, and cerebrospinal fluid analysis failed to confirm a diagnosis. Steroids were discontinued, and a repeat biopsy was performed two months later after symptomatic and radiologic progression. Pathology analysis determined a diagnosis of diffuse large B-cell lymphoma. This case highlights the classic imaging and MRS findings associated with PCNSL and underscores the diagnostic challenges posed by continued corticosteroid use, which can lead to false-negative biopsy, cytology, and flow cytometry. Avoiding unnecessary delays in diagnosing PCNSL is critical, as timely initiation of targeted chemotherapy improves outcomes. When MRI and MRS findings support a diagnosis of PCNSL, physicians may opt for early biopsy and avoid steroids even if cerebral edema is present. This case also supports the growing role of MRS as a valuable adjunct in characterizing CNS lesions - especially when biopsy is non-diagnostic or contraindicated. Further research and standardization of MRS techniques may enhance its utility in non-invasively diagnosing PCNSL in the future.