Teaching Case

A 58-year-old man who had been recently diagnosed with lung cancer presented with acute onset walking difficulty.

The patient was submitted to spinal cord MRI. T1WI, T2WI, and T1WI+Gad in the sagittal plane were acquired, which revealed an intramedullary mass extending from the level of T11 to L1. On the T1WI the lesion was isointense to the spinal cord (figure 1). On the T2WI it was inhomogeneously iso-/hyperintense (figure 2a); the lesion was surrounded by a rather disproportionate degree of spinal cord oedema (figure 2b). On the T1WI+Gad the lesion exhibited the "flame sign", with flame-shaped enhancement at the cranial and caudal borders of the lesion (figure 3). There was no evidence of vertebral lesions.
The patient was subsequently treated with radiotherapy.

Intramedullary spinal cord metastases (ISCMs) are uncommon, i.e. 0.9%–2.1% in cancer patients [1]. ISCMs are found, in descending order, in the cervical (45%), thoracic cord (35%) and the lumbar region (8%) [2]. The majority of ISCMs are solitary, occupying the length of 2-3 vertebral bodies [3].
Primaries causing ISCMs in descending order are: Lung (40–85%), breast carcinoma (11%), melanoma (5%), renal cell carcinoma (4%), colorectal carcinoma (3%), and lymphoma (3%). Unknown primaries account for 5% [2]. Spread routes include haematogenous (arterial supply), direct extension along the leptomeninges and growth along the Virchow-Robin spaces [1]. Extension through the central canal has been suggested [4]. Dissemination along the Batson venous plexus in retroperitoneal primaries or extension along perineural lymphatics is another possible mechanism [1].
Almost every patient presents with motor weakness. Other symptoms are pain (70%), bladder/bowel dysfunction (60%), and paresthesias (50%). Typically there is rapid decline in the neurologic status, with symptoms duration less than 1 month [2], at diagnosis, as opposed to long duration symptoms of spinal primaries.
Patients with ISCMs usually have normal radiographs. Conventional myelography won’t pick-up the lesion in up to 40% [2]. CT myelography may better demonstrate these lesions.
MR imaging is the modality of choice for the detection of ISCMs, and may reveal more lesions, clinically unsuspected [5].
On the MRI, lesions produce cord expansion. On T1-WI, there may be a central area of low signal intensity. On T2-WI, there is high signal intensity (oedema or tumour infiltration). Cysts are not usually found, in contrast to primaries. ISCMs usually show intense, homogeneous enhancement. They are surrounded by extensive oedema, disproportionate to the lesion size [6].
The flame sign is recently described as an ill-defined flame-shaped region of gadolinium enhancement at the superior and/or inferior margin of an otherwise well-defined lesion [7]. Another sign described in the same study is the rim sign, which is a more intense thin rim of peripheral enhancement around an enhancing lesion, on the axial images; it may be complete, or incomplete. ISCMs may exhibit either one of the signs, or both signs. The rim and flame signs are more common in ISCMs and are rarely found in primary spinal cord masses.
Patients with ISCMs have a dismal prognosis as two-thirds of them die within 6 months from the diagnosis. Radiation and corticosteroid treatments are mainly used, in cases of radiosensitive tumours [2]. However, microsurgical resection for discrete, well-defined lesions has also been advocated [2].
The flame sign may help favour the diagnosis of an ISCM over a primary.