Chordoma and Chondroma/Chondrosarcoma

Abstract

Both CT scanning and MRI are usually necessary for the complete evaluation of these tumors because of the involvement of both soft tissue and bony structures at the skull base. Chordomas are rare tumors that derive from embryonic remnants of the notochord. Cranial chordomas arise mainly from the clivus and are locally destructive. Clival chordomas represent less than 0.2 % of all intracranial tumors. They can be encountered in all age groups, with a peak in the fourth decade of life. Gender ratio is 2:1 (male/female) and there is no racial predilection. Cranial chordomas most often originate from the spheno-occipital synchondrosis, and thus typically have a midline location. Occasionally chordomas may arise unilaterally in the skull base from the petrous apex. They may spread to sellar and parasellar area, posterior fossa, and nasopharynx. Clinical symptoms depend on the direction of tumor growth. Sellar chordomas usually present with hypopituitarism and chiasmal compression. Parasellar chordomas present with hypopituitarism, oculomotor nerve palsy, and optic tract compression. Purely clival chordomas are characterized by headache, cranial nerve palsy, and brainstem compression. The abducens nerve is the most commonly affected. They usually are locally aggressive and frequently recur, but metastases are very rare. Sarcomatous degeneration and dedifferentiation have been reported. There are three histological subtypes of chordomas: classic, chondroid, and dedifferentiated. Chordomas are characterized by foamy, vacuolated, physaliferous cells within a myxoid stroma, and usually cause extensive bone destruction of the skull base, best analyzed on CT. CT will also show frequent intratumoral sequestered bone fragments. MRI typically shows a destructive invasive soft tissue mass arising from the clivus. At an early stage, bone expansion indicates that the tumor originates from bone and not adjacent structures. The extension of chordomas is primarily posterior, with involvement of the pontine cistern and, occasionally, the premedullary cistern. On MRI, posterior extension may show as a thumb indenting the pons and/or of the medulla (Fig. 37.1). Extension can be upward to the sella turcica, displacing the pituitary gland, downward to the nasopharynx, or laterally to the middle cranial fossa. Most chordomas demonstrate T1 hypointensity and T2 hyperintensity, with suggestive hypointense intratumoral septations (Fig. 37.2). Foci of T1 hyperintensity may be depicted within the tumor or at its periphery, which represent residual bony fragments, calcifications, mucoid material, or hemorrhage (Fig. 37.3). Following gadolinium administration, chordomas usually show lobulated areas with a honeycomb appearance. Enhancement is variable: it can be mild, intense, or absent. Overall, the signal in chordomas is heterogeneous on all sequences on T1 and T2 WIs and after gadolinium administration (Fig. 37.4). Low ADC values have been found in the dedifferentiated histological variant ecchordosis physaliphora, also derived from notochord remnants. Knowledge of this entity is merited because it is considered as a benign congenital malformation and thus differs from chordoma, which is a true tumor. It is usually asymptomatic. Pontine hemorrhage or CSF fistula associated with ecchordosis physaliphora have been reported. Ecchordosis physaliphora is a midline intradural retro-/intraclival lesion inducing a bony clival defect without aggressive features. Its signal is similar to CSF on T2 and T1 WIs with no enhancement after gadolinium infusion (Fig. 37.5). When detected, the bony stalk attachment to the clivus is considered a characteristic sign. It can be seen on CT or on thin high-resolution MR sequences. Chondromas and chondrosarcomas of the skull base are uncommon cartilaginous tumors that develop from embryonic cartilaginous remnants enclosed in the cranial base synchondroses. They most often arise from the petro-occipital synchondrosis and have a lateral location in the parasellar area, at the foramen lacerum level. They may also arise from the spheno-occipital synchondrosis with a midline location. Chondromas of the sella turcica have been reported, for which there is no gender predilection; they are often diagnosed between the third and fourth decade. Chondromas and chondrosarcomas occur at higher frequency in Ollier disease and Maffucci syndrome. The most common presentation symptoms are deficits of the cranial nerves, including the abducens, optic, acoustic-facial, and lower cranial nerves, and headaches. The onset of symptoms is usually gradual. Endocrine dysfunction has been reported in sellar chondromas. On histologic examination, chondromas consist of mature, well-differentiated hyaline cartilage. Total excision is curative, with no recurrence. Chondrosarcomas are malignant tumors composed of atypical chondrocytes, whose nuclei are hyperchromatic and enlarged. There are three histological subtypes of chondrosarcomas, ranging from grade I (well differentiated) to grade III (poorly differentiated). They display chondroid calcifications in more than half of the cases. CT is required to evaluate intratumoral calcification and bone erosion (Fig. 37.6). On MRI, these tumors appear hypointense or isointense on T1WI and heterogeneously brightly hyperintense on T2WI (Fig. 37.7). They enhance poorly in a heterogeneous fashion, with linear and nodular areas (Fig. 37.8). The typical chondroid calcifications are curvilinear and usually appear hypointense on MR spin-echo sequences. However, they may appear hyperintense T1WIs depending on the degree of mineralization. On ADC maps these tumors are usually bright, reflecting high diffusion.