Clival Chordoma

Chordomas are tumors originating from embryonic remnants of the primitive notochord. Since chordomas lie in bone, they are usually extradural and induce bone destruction. Fluid and gelatinous mucoid substance (associated with recent and old hemorrhage) and necrotic areas are found within the tumor; in some patients, calcification and sequestered bone fragments are found as well. The variety of these components may explain the signal heterogeneity observed on MRI. Incomplete delineation of the tumor and microscopic distal extension of tumor cells may explain the frequency of recurrences.
Metastatic spread of chordomas is observed in 7-14% of patients with lymph node, pulmonary, bone, cerebral, or abdominal visceral involvement, predominantly from massive tumors. True malignant forms of chordomas occasionally have areas of typical chordoma and undifferentiated areas, most often suggestive of fibrosarcoma; the prognosis is poor.
Clival chordomas are benign tumors but because of their critical location, local invasion, recurrence, and occasional metastatic spread, their prognosis is similar to that of malignant tumors.
MRI and CT scan have complementary roles in the evaluation of chordoma. CT evaluation is needed to assess the degree of bone involvement or destruction and to detect patterns of calcifications within the lesion. MRI provides excellent 3-dimensional analysis of the posterior fossa (especially the brainstem), sella turcica, cavernous sinuses, and middle cranial fossa. MRI depicts calcifications and the precise involvement of skull base osteolysis less well than CT, especially for skull base foramina.
3-D gradient-echo T1-weighted sequences are helpful since they visualize the tumor in 3 planes within a short time and with good analysis of tumoral signal.
Skull base chordomas are well delineated at the outset since they displace adjacent structures; however, more advanced tumors become invasive and have a pseudomalignant appearance with bone erosion and soft tissue invasion.
Most chordomas exhibit high signal on T2-weighted images, which is nonspecific.
Following gadolinium injection, chordomas usually show heterogeneous lobulated areas with a honeycomb appearance corresponding to low T1 signal areas within the tumor. The pattern of contrast enhancement can be related to the pathologic features of the tumors, which are organized in lobules with mucinous and gelatinous contents. This may be a useful diagnostic sign. The borders of the tumor are better delineated with gadolinium injection.
Reference: Doucet V, Peretti-Viton P, Figarella-Branger D, et al: MRI of intracranial chordomas. Extent of tumour and contrast enhancement: criteria for differential diagnosis. Neuroradiology 1997 Aug; 39(8): 571-6.
Credit: Dr Abhijit Datir
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