Asymptomatic cauda equina metastasis in a patient with nasopharyngeal carcinoma: Detection by ¹⁸F-FDG PET/CT

INTRODUCTION

The central nervous system (CNS) metastasis from nasopharyngeal carcinoma (NPC) is an extremely rare occurrence, although direct intracranial invasion is not infrequent in patients with NPC. ¹⁸F-Fluordeoxyglucose (¹⁸F-FDG) positron emission tomography-computed tomography (PET-CT) is an excellent tool for staging NPC. Here we present a case where ¹⁸F-FDG PET/CT scan detected an asymptomatic cauda equina metastatic lesion in a patient with NPC and helped in change of management.

CASE REPORT

A 62-year-old male was presented with history of neck swelling, nasal obstruction and epistaxis. On examination, bilateral cervical lymphadenopathy was noted. A well-defined soft tissue density lesion at nasopharyngeal region abutting the posterior pharyngeal wall was also noted. Biopsy from the nasopharyngeal mass was done and it showed undifferentiated carcinoma. The patient was referred for whole body ¹⁸F-FDG PET/CT for staging.

PET/CT revealed ¹⁸F-FDG avid primary malignant disease involving the roof and posterior wall of nasopharynx and bilateral fossa of rossenmuller, with metastases to bilateral cervical and left supraclavicular lymph nodes. Interestingly, a discrete ¹⁸F-FDG avid (SUVmax-8.6) nodular lesion was noted in the cauda equina region at the level of L4-L5 vertebrae, which was highly suggestive of metastasis [Figure 1]. This lesion was later confirmed to be metastatic at contrast-enhanced magnetic resonance imaging (MRI) and the patient was referred for regional radiotherapy. The patient then underwent chemotherapy and regional radiotherapy to cauda equina lesion.

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Figure 1 ¹⁸F-FDG PET/CT study for staging. PET/CT revealed ¹⁸F-FDG avid primary malignant disease involving the roof and posterior wall of nasopharynx and bilateral fossa of rossenmuller (a and b; broken arrow), with metastases to bilateral cervical and left supraclavicular lymph nodes (a and c; arrows). A discrete 18F-FDG avid nodular lesion was noted in the cauda equina region at the level of L4-L5 vertebrae (a,d-g; bold arrow)

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DISCUSSION

Nasopharyngeal cancer is the head and neck cancer with the highest incidence of distant spread. The most common distant metastatic sites are bone, lung and liver in descending order.[1] While intracranial invasion by direct extension from the nasopharynx is a common finding in locally advanced NPC, CNS metastasis of NPC is an extremely rare occurrence.[23] All the reported cases of spinal cord metastases have been associated with locally advanced disease.[345] The possible mechanism of metastases is hypothesized to be dissemination through the cerebrospinal fluid. Because of complications associated with tissue diagnosis, imaging plays a vital role in diagnosis of spinal cord metastasis. ¹⁸F-FDG PET/CT can play an important role in this aspect.[6] Also, in our case ¹⁸F-FDG PET/CT played a critical role in detection of the metastatic cauda equina lesion.

Although, cauda equina metastasis in NPC has been documented in literature,[7] to the best of our knowledge, the present case is the first one reporting the utility of ¹⁸F-FDG PET/CT for detecting asymptomatic spinal cauda equina metastasis in nasopharyngeal carcinoma. By demonstrating distant metastasis to cauda equina, ¹⁸F-FDG PET/CT detection changes the management in this patient.