Spinal cord metastases typically affect the vertebral column or extradural space, whereas intramedullary metastases are uncommon and are typically associated with advanced and invasive systemic cancers. Consequently, ISCM is a rare clinical diagnosis, and clinicians frequently overlook the underlying cause owing to a lack of awareness and research. Multiple studies have discovered that ISCM accounts for only 4.2–8.5% of central nervous system metastases, less than 5% of spinal metastases, 1–3% of intramedullary tumours, and 0.6% of spinal cord tumours. On the other hand, astrocytoma and ependymomas are the most common intramedullary lesions [1,9–13].
According to previous research [6], lung cancer (42.4%), breast cancer (15.5%), melanoma (7.2%), and renal carcinoma (6.7%) are the most prevalent causes of ISCM. Papillary thyroid carcinoma is the primary source of ISCM among thyroid malignancies [5,14–18], followed by mixed papillary and follicular thyroid carcinomas [19], anaplastic thyroid carcinomas [20], and undifferentiated thyroid carcinomas [21].
To the best of our knowledge, this is the first report of an association between ISCM and pure thyroid follicular carcinoma. They are low-grade tumours with limited metastatic potential owing to their favourable prognosis, high survival rate, and high cure rate. Nevertheless, it can spread infrequently. In this case, it can spread via direct invasion, spinal fluid, hematogenous, lymphatic, or retrograde endoneurial pathways, with the lungs and bones being involved in most cases [22].
ISCMs can be challenging to diagnose because their MRI characteristics are comparable to those of astrocytomas and ependymomas: isointense to hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging. Post radiation myelitis may also manifest comparably. Although there are some similarities in contrast enhancement patterns, there can be some differences, such as intense homogenous enhancement in ISCMs, patchy enhancement in astrocytoma, inhomogeneous enhancement in ependymomas, and focal homogeneous enhancement in post-radiation myelitis [23]. Therefore, histopathology is the gold standard for diagnosis. The following conditions should be considered when evaluating the hazards of biopsy: When MRI reveals a tumour, the primary objective is total resection. If MRI reveals a non-neoplastic condition, systemic symptoms or disease progression may serve as diagnostic markers [24].
Based on MRI data, we initially suspected astrocytoma and ependymomas because intrathoracic spinal cord intramedullary lesions are less likely to be metastatic. In the absence of active disease or metastases, astrocytomas and ependymomas account for > 90 percent of intramedullary spinal cord malignancies. In addition, since most ependymomas are amenable to surgical removal, they differ significantly from astrocytoma [1,25,26]. Previous research has indicated that ependymomas may elicit similar symptoms in individuals aged > 30 years with well-defined central spinal cord masses. Consequently, we investigated ependymomas as possible initial diagnoses. [23,27,28].
In the present case, pure thyroid follicular cancer induced ISCM. Given the absence of bone or brain involvement, cancer must have progressed hematogenously or retrogradely through the endoneurium, rather than locally from the vertebrae or spinal fluid. It took approximately five years in our case for ISCM to be diagnosed, although most cases of ISCM were diagnosed within one year after the detection of the underlying malignancy. Therefore, clinicians should be aware that ISCM may be present in patients with cancer with typical neurological deficits and MRI findings. In addition, the literature has shown a long latency between primary malignancy and ISCM in the thoracic and thoracolumbar regions, e.g., up to ten years, for ISCM in the thoracic and thoracolumbar regions [13].
O'Neill et al. [6] noted that ISCM usually manifests as weakness, sensory impairment, and bowel or bladder dysfunction, which is consistent with our case. Nevertheless, Brown-Sequard syndrome is a rare symptom of ISCM.
Previously, only 5% of these cancers were diagnosed before death. Although cancer survival rates have increased owing to improved diagnostic and treatment methods, the incidence of ISCM has increased in recent years. Since the development of ISCM is generally accompanied by dramatic deterioration in brain function and catastrophic results, prompt identification and treatment are crucial [29].
Before intraoperative imaging guidance and microsurgery, surgical treatment had no noticeable effect on the survival of patients with ISCM. Their prognosis consisted of a median survival rate of four months. Surgical therapies can now extend survival owing to breakthroughs in surgery and technology. According to Kalita et al., surgical patients may live beyond 9.4 months. Individuals with radioresistant primary tumours or solitary intramedullary lesions may benefit from surgical excision if they are diagnosed with cancer in the early stages accompanied by rapidly growing neurological impairment. When a single ISCM lesion with limited systemic metastases is present, surgical intervention may be beneficial to rule out other pathologies, such as primary intramedullary tumours, or when the primary tumour is unlikely to spread to the spinal cord parenchyma (such as thyroid, prostate, or esophageal cancer) [13,30]. As shown in the literature, since neurological status prior to the intervention is the most significant indicator of a favourable functional outcome, early detection and intervention play a crucial role in reducing mortality and morbidity.