24 Chondrosarcomas
Abstract
Pediatric chondrosarcomas of the skull base are extremely rare malignant tumors. They are indolent but have a propensity for recurrence if inadequately treated. The best treatment plan is still a subject of discussion. Total or near-total surgical resection followed by radiotherapy seems to be the option with the best outcomes. The approach is usually selected based on the involvement of cranial nerves, the location of the tumor, and the surgeon’s experience. The endoscopic endonasal approach using the ventral transnasal corridor is an effective approach for their surgical management since it provides a direct exposure of the petroclival synchondrosis.
24.1 Introduction
Sinonasal and skull base lesions in childhood have distinct clinical presentations and outcomes depending on the child’s age, tumor’s location, and lesion’s pathology. 1
Chondrosarcomas are infrequent lesions with predilection for long bones and pelvis, with only 10% occurring in the head and neck. 2 They represent 6% of skull base lesions and 0.15% of all intracranial tumors. 3
Pediatric chondrosarcomas of the skull base are extremely rare malignant tumors with a challenging treatment because of their location. They are indolent but have a propensity for recurrence if inadequately treated. 3
Chondrosarcomas arise from cells of chondroid origin and can be composed of myxoid cartilage, hyaline cartilage, or a combination of both of these matrices. 4 They commonly originate from the petroclival synchondroses. Unlike chordomas, which tend to be midline, chondrosarcomas usually arise in a paramedian location. 5 In the skull base, more than half of chondrosarcomas arise in the middle fossa, 14% involve both middle and posterior fossae, 14% occur in the anterior fossa, and 7% originate in the posterior fossa. 5
The histological classification of chondrosarcomas is divided into four groups: conventional (majority), mesenchymal (<10%), clear cell, and dedifferentiated. The major histological differential diagnosis is chondroid chordoma, which has the presence of notochordal elements. 6 The prognosis is determined primarily by its World Health Organization (WHO) histological grade. By the analyses of histological features, such as cellularity, nuclear size, mitotic rate, and frequency of lacunae with multiple nuclei, this grading system includes three categories: grade I (well differentiated), grade II (moderately differentiated), and grade III (poorly differentiated). 3
Imaging studies, such as computed axial tomography scan (CT) and MRI, are important for diagnosis and planning the surgical approach. Bony destruction of the skull base lateral to the midline is usually found on CT. MRI is useful to evaluate tumor involvement of neural and vascular structures. Chondrosarcomas have low-to-intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Heterogenous enhancement is usually seen following administration of contrast material. 5
Symptoms most commonly arise from cranial nerve or brainstem compression: diplopia, hoarseness, dysphasia, facial dysesthesia, hearing loss, headache, and gait disturbances. 5 An important factor in approach selection for these tumors is the presence of particular cranial nerve deficits at presentation. 4
24.2 Management Options
The differentiation between chordomas and chondrosarcomas of the skull base is necessary to define final treatment. Both lesions have very similar appearances and radiological characteristics, making imaging alone not reliable to differentiate them. 7
The prognosis of chondrosarcomas is grounded on three pillars. The first is extent of tumor resection. The second pillar is the tumor histological grade. Grade III tumors have worse prognosis than grade I and II tumors. Adjuvant radiotherapy treatment is the third pillar, and it seems to improve survival rates. The best treatment plan is still controversial. Most treatment regimens with the best outcomes involve total or near-total surgical resection followed by radiotherapy. 7
24.2.1 Surgical Resection
Surgical resection of the tumor is necessary to obtain a definitive tissue diagnosis. Maximal safe surgical resection is the primary consensus for initial treatment of chondrosarcoma. The main goals of surgical treatment are decompression of neurovascular structures and removal of the tumor near important neural structures like the brainstem in order to allow safe high-dose radiotherapy. 6
The approach is usually selected based on the involvement of cranial nerves and tumor location. Chondrosarcomas often destroy the pericranial layer of the dura, and they often only displace the meningeal layer of dura instead of transgressing it. Consequently, cranial chondrosarcomas are generally located completely extradurally, with origin on the petroclival synchondrosis, and with potential extension to the middle fossa, posterior fossa, and superior cervical space around the jugular foramen. Because of these characteristics, the ventral transnasal corridor is the most direct and effective extradural approach for their surgical management. 8
Extensive skull base chondrosarcomas may have higher morbidity related to radical surgery, which leads some surgeons to advocate for a less radical resection as the surgical goal. A safe cytoreduction followed by radiotherapy to residual tumor would result in lower morbidity, and therefore better quality of life. Radical excision or cytoreduction with adjuvant radiotherapy seems to offer similar 5-year tumor recurrence rates of 70 to 80% and overall survival rates of 80 to 90%. 4 We believe, however, that radical resection should always be the primary goal of the surgical strategy, and the decision to leave residual should be an exception based on intraoperative detection of potential morbidity related to its resection.
24.2.2 Radiotherapy
Radiotherapy as an adjuvant treatment for chondrosarcomas has been increasingly accepted to improve both tumor-free survival and overall survival. 2 The proximity to important structures such as the brainstem, cranial nerves, optic pathway, and temporal lobes, along with the fact that skull base tumors require high-radiation doses, are important considerations in choosing the adjuvant therapy. 9 Conventional fractionated photon radiotherapy, stereotactic radiosurgery, and proton therapy are the most used methods to administrate radiation to the skull base. 7 The true concern over radiation on infant patients with chondrosarcoma is the fact they would live to experience the side effects from radiotherapy.
Proton therapy has physical properties that spare normal tissues and reduce the integral dose, making it increasingly recognized as the preferred treatment for childhood cancer. 9 Numerous short follow-up clinical studies involving small numbers of patients have suggested a satisfactory clinical outcome using protons on children with chondrosarcoma. Proton therapy has been correlated with less complications compared to other radiotherapy modalities. 4
24.2.3 Chemotherapy
Chemotherapy has not been an effective option for the treatment of chondrosarcomas. It can be used with a very limited proven efficacy in patients with advanced chondrosarcoma, such as mesenchymal grade III tumors. 10
24.3 The Role of Endoscopic Endonasal Surgery
The main challenges of endoscopic endonasal surgery in the pediatric population are small working spaces and the possibility of lack of pneumatization. Neuronavigation is very helpful to allow for safer access in the absence of key landmarks. 1 The team should have experience with skull base pathologies and pediatric care.
Endoscopic endonasal approaches (EEA) provide the most direct access to the ventral skull base. Chondrosarcomas usually originate in the petroclival region and tend to displace neurovascular elements laterally, superiorly, and posteriorly. For that reason, we advocate the use of EEA as the initial surgical corridor. 6 In a single procedure, EEA allows access to multiple skull base compartments, avoiding extensive retraction of neurovascular structures. It also allows extensive drilling of the clivus, sphenoid bone, and petrous portions of the temporal bone, which are frequently invaded by tumors. 8
For lesions located in the upper petroclival region, cavernous sinus, and middle cranial fossa, the transsphenoidal approach, with removal of the sphenoid and temporal bony encasement is indicated. Tumors extending into the middle third of the clivus can be approached through a transsphenoidal approach along with clivectomy and petrosectomy. Lesions in the lower clivus and infratemporal fossa require a transpterygoid approach. 6
24.3.1 Surgical Technique
The surgery is performed under general anesthesia with orotracheal intubation. Prophylactic antibiotics are given. The patient is positioned supine, with the head fixed on the Mayfield head holder. The neck is slightly extended and the head turned to the right and tilted to the left. Nasal irrigation with oxymetazoline hydrochloride solution and facial/nasal decontamination with iodine solution is performed. The abdomen and the right thigh are also prepped in case fat or muscle grafts are necessary.
The surgical approach is initially comprised of right middle turbinectomy, bilateral posterior ethmoidectomies, elevation of the nasoseptal flap (NSF), 11 and posterior septectomy. Reverse flap (incision and rotation of the now-exposed contralateral septal mucosa to cover the denuded septum) is usually performed. 12 A large sphenoidotomy by drilling of the sphenoid floor until it is flush with the clivus is the next step. In order to access the pterygopalatine fossa, the removal of the posterior wall of the maxillary sinus is necessary and allows identification of the infraorbital and vidian nerve. The vidian nerve may be spared or sacrificed by drilling of the vidian canal, which is also a landmark for the foramen lacerum (▶ Fig. 24.1). 13 In sequence, the drilling of the clivus is performed, and it needs to be taken into account that massive venous bleeding from the basilar plexus can occur. It can be managed using direct infusion of hemostatic products. The petrous apex drilling and the skeletonization of the internal carotid artery (ICA) must be done (▶ Fig. 24.2). 8
Depending on the location of the tumor, some other steps may be necessary. Tumors located inferior to the petrous apex may require removal or mobilization of the Eustachian tube. 8 The infratemporal fossa can be accessed by removing the pterygoid processes and adjacent musculature. In order to gain access to the anterior portion of Meckel’s cave and the medial middle cranial fossa, the lateral sphenoid recess must be accessed. 14
Chondrosarcomas are often soft; however, sometimes they can be hard and very calcified. Usually, the tumor’s resection starts within the petrous apex. Lateralization of the ICA allows the removal of the tumor located on the petroclival synchondrosis. Dissection within the cavernous sinus, jugular foramen, infratemporal fossa, and high cervical region is performed using stimulating dissectors to prevent cranial nerve injuries. The presence or absence of a cerebrospinal fluid (CSF) leak guides the type of skull base reconstruction. If present, the dural defect is plugged with a partial inlay/onlay sheet of collagen matrix and covered with the NSF. In the absence of CSF leak, the flap is positioned over the exposed ICA for protection. 8
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