Differential Diagnosis of Clival and Spinal Tumors

Ecchordosis Physaliphora

Ecchordosis physaliphora (EP) is a benign congenital lesion derived from ectopic notochord remnants along the midline of the axial skeleton. EP arises intradurally and is not associated with bone erosion. Although EP of the spine is very rare, clival region EP is found in up to 2% of random autopsies. Ecchordosis are often clinically silent and discovered incidentally ; reports of clinically apparent EPs are scarce. In contrast, almost all clival chordomas arise extradurally, erode bone, and present clinically, causing pain, cranial neuropathies, and signs of brainstem compression.

In 1987, Wolfe and Scheithauer described a set of extraosseous chordomas having a better prognosis than classical chordomas. They distinguished these from both EP and osseous chordoma with the term “intradural chordoma.” Other pathologists contend that EP is a precursor, or even a benign form, of chordoma.

In the preoperative clinical settings, the distinction between EP and an intradural chordoma is greatly influenced by the clinical picture, particularly growth suggestive of a chordoma, and other radiologic findings. The distinction between these two lesions solely based on histologic and ultrastructural analysis of small tissue samples can be very difficult (see Chapter 2 ). Infiltrative growth, positive staining for brachyury, and an MIB-1 labeling index (i.e., cellular proliferative potential) > 2% favor chordoma.

Radiologically, EP is hypointense on T1-weighted and hypertintense on T2-weighted MR images. Distinct from an intradural chordoma, which shows considerable contrast enhancement, EP does not enhance after contrast injection. Wang et al. reported that EPs are usually smaller than chordomas, with a maximum diameter of less than 2 cm. However, as others have described EPs with diameters of 3 and 4 cm, agreement regarding the distinguishing features of large symptomatic EPs (>2 cm) and intradural chordomas is lacking. Lastly, CT imaging of a presumed EP revealed a small pedicle-like hypertrophic change in the inner table of clival bone, devoid of erosion, just anterior to the intradural mass. In general, asymptomatic patients can be treated conservatively if radiological follow-up shows a small intradural mass that does not enlarge.

Benign Notochordal Cell Tumor

Benign notochordal cell tumor (BNCT), previously called giant notochord rest or notochordal hamartoma, is an intraosseous lesions believed to be a potential precursor of chordomas. Distinct from ecchordosis physaliphora , which occur far more frequently in the skull base, BNCTs have an anatomic predilection for the spine, mainly the sacrococcygeal region. These tumors, usually microscopic in size, are located centrally within the vertebral body and are most often discovered incidentally during autopsies. In fact, small BNCTs are reported to be present in the spine of up to 20% of the population. Macroscopic BNCTs, on the other hand, are quite rare and proper differentiation of this entity from spinal chordoma is of utmost importance since the prognosis and management is completely different. Clinical observation and radiological surveillance with MR imaging is recommended for patients with a presumed diagnosis of BNCT.

As with ecchordosis, MR imaging of BNCT demonstrates low T1 signal, and high T2 signal with intraosseous lesion lacking contrast enhancement. Absence of a soft-tissue mass is also characteristic. On CT, BNCTs appear sclerotic and lack osteolytic changes. Histologically, these lesions are characterized by intraosseous sheets of adipocyte-like vacuolated chordoid cells mixed with eosinophilic cells and absence of myxoid background. Nuclei may appear atypical but mitotic figures are not identified. BNCTs also stain positively for cytokeratin-18. Nevertheless, the differential diagnosis between BNCTs and chordomas can be very difficult as these lesions share a similar histological and immunohistochemical profile. As for EP, the diagnosis of BNCT is greatly influenced by the clinical picture and radiological findings. Table 6.2 summarizes the main differences between EP/BNCTs and chordomas.

Chondroma

Chondromas, also named as osteochondromas, are benign tumors composed of mature hyaline cartilage that most commonly arise from the cartilaginous growth plates of long bones, pelvis, and scapulae. They may be solitary or multiple, in which case the term multiple exostosis applies. When they arise within the medullary osseous cavity, they are called enchondromas and can be a part of either Ollier’s disease or Maffucci syndrome—two different types of enchondromatosis that consist of multiple endochondral bone cysts and soft tissue/visceral hemangiomas, respectively. Vertebral involvement occurs in approximately 7% of the patients and 60% of these lesions arise in the cervical spine, with a predilection for the craniovertebral junction. Skull base chondromas usually arise from embryonic chondrocytic cells remnants located in sphenopetroclival synchondrosis and are rare.

These tumors may become symptomatic during adolescence as their growth rate tends to increase with age. Once the nearest epiphyseal center closes, the tumor growth stops. Malignant transformation should be considered if tumor growth persists into adulthood. Spinal chondromas usually manifest as a painless, slow-growing lesion, while skull base chondromas present with chronic headache and, eventually, intracranial hypertension. Neurological deficits may occur and depend on tumor location and growth pattern. Surgical resection is the treatment of choice.

CT imaging reveals a well-circumscribed, calcified mass, associated with erosion of the surrounding bone. MR imaging commonly shows a mass that is hypointense on T1-weighted images and heterogeneously hypertintense on T2-weighted images. A characteristic peripheral hypointensity, representing mature hyaline cartilage, is commonly seen on T2 weighted imaging. Contrast enhancement is often mild to moderate. Histologically, chondromas display an expansile, noninfiltrative growth pattern and contain well-differentiated cartilaginous cells, low cellularity, and no mitosis. Nonetheless, the differentiation between chondromas and low-grade chondrosarcomas may be challenging.

Chondroblastoma

Chondroblastomas are rare primary cartilaginous tumors that commonly occur in the epiphyses of long bones during adolescence and early adulthood. Skull base and spine chondroblastomas are very rare, tend to affect older people, and usually arise in the temporal bone and cervical spine, respectively. Clinically, these neoplasms may present with local pain, neurological deficits, or a painless, nontender, firm swelling. Although considered benign, these lesions may be locally aggressive and, exceptionally, become malignant. Therefore, some authors recommend a preoperative work up for metastatic disease. Surgery is the main treatment modality with the aim of total resection to avoid recurrences. Radiation therapy can be considered for recurrent disease.

CT imaging often reveals an osteolytic soft-tissue mass with internal calcification and, in some cases, enhancement following contrast injection. MR imaging shows low to intermediate signal on T1-weighted images, a heterogeneous, high signal on T2-weighted images, and heterogeneous contrast enhancement.

Tissue examination reveals a chondromyxoid stroma surrounding sheets of mononuclear polyhedral cells (chondroblasts) admixed with osteoclastic-like giant cells. Zones of lacy calcification (i.e., “chicken wire”) are a distinctive finding. Moreover, these tumors stain positively for S-100 and vimentin. Table 6.3 summarizes the main characteristics and differences between chondromas and chondroblastomas.

Osteoma and Osteoblastoma

Osteomas are benign osseous neoplasms that commonly occur in patients during the second and third decade of life. They have a propensity to involve the posterior elements of the vertebra in the spine, but occur more frequently in the cranial vault and paranasal sinuses in the skull, especially the frontoethmoidal region. The skull base (i.e., clivus) is rarely affected. These tumors may be also a part of Gardner’s syndrome (multiple cranial osteomas, soft-tissue tumors, and colonic polyposis). Osteoblastomas, although histologically similar to osteomas, tend to occur in slightly older patients, have a greater propensity to involve the spine, may behave more aggressively, and undergo malignant transformation.

Pain, including painful scoliosis, is the most common clinical manifestation of spinal lesions. For osteomas, characteristically, pain is more intense at night and responsive to salicylates. These features are not commonly observed in osteoblastomas. Radiculopathy and neurological deficits may be present and are more common in osteoblastomas (up to 70% of cases). Skull base tumors are often asymptomatic but may present with headaches, visual symptoms, and, rarely, spontaneous rhinorrhea and signs of central nervous system infection (i.e., meningitis and brain abscess).

Radiologically, osteomas present as a well-demarcated, hyperdense intraosseous tumor with a diameter smaller than 2 cm. Osteoblastomas are larger (>2 cm), may be predominantly osteolytic, and extend into the soft tissue thus resembling other malignant tumors. MR imaging often reveals a hypo- to isointense tumor on T1- and T2-weighted images corresponding to foci of calcification. Osteoblastomas enhance avidly following contrast injection. Histologically, these tumors show increased osteoid tissue formation surrounded by a vascular fibrous stroma and perilesional sclerosis. The osteoid production and vascularity are more intense in osteoblastomas.

Asymptomatic tumors should be treated conservatively. Radiological signs of tumor progression, intractable pain, and presence of neurological symptoms warrant surgical intervention. Adjuvant radiotherapy is reserved for recurrent cases. Table 6.4 summarizes the main differences between osteomas and osteoblastomas.