3. Methods (differential diagnosis, investigations and treatment)
After a thorough history and physical examination, we had a number of differential diagnoses, namely, hematoma, cyst, chronic abscess and neoplastic growths like rhabdomyosarcoma, soft tissue sarcoma, etc. The T1w Magnetic Resonance Imaging (MRI) of pelvis showed a 6.3x9.5x8 cm sacral mass, with heterogenous post-contrast enhancement, as shown in figure 1. There was diffuse cortical break with associated large extraosseous soft tissue mass, with involvement of spinal canal and exiting sacral nerve roots. Bilateral gluteal muscles were involved, with greater involvement on the right side. The presacral extension displaced the rectum anteriorly without any bowel invasion. Few subcentimetric indeterminate pelvic nodes were noted. The possible differentials now were sacral chordoma and sacral teratoma. Biopsy taken from the lesion revealed a poorly differentiated chordoma with fibrocollagenous tissue infiltrated by tumor arranged in sheets. Individual cells were pleomorphic, round to oval with coarse chromatin, prominent nucleoli and abundant eosinophilic to clear cytoplasm. There were foci of calcification with ~8/10hpf mitotic figures and no necrosis. On immunohistochemistry (IHC), tumor cells stained positive for AE1/AE3 and brachyury and negative for SOX10, S-100, and desmin. The histological and IHC images have been illustrated in figure 2. 18-fluorine-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET) CT was done for metastatic work-up, and showed a 9 mm, FDG avid nodule in upper lobe of left lung, with maximum standardized uptake value (SUVmax) being 4.58.
The patient’s sacral lesion was deemed unresectable in view of large size and potential sacral instability as well as loss of bladder and bowel control post resection. CT-guided biopsy from the left upper lobe confirmed poorly differentiated metastatic chordoma, with lung parenchyma and fibro collagenous tissue infiltrated by tumor cells arranged in sheets and focal cords. Tumor cells exhibited moderate pleomorphism, round to oval hyperchromatic nuclei, inconspicuous nucleoli, eosinophilic to vacuolated cytoplasm. Focal myxoid change and focal areas of necrosis were identified. On IHC, tumor cells stained positive for Brachury (diffuse), AE1/AE3 (diffuse), S-100(focal) and negative for CK7, Napsin A and TTF1. The intent was kept curative as the single metastatic lesion was small and was found amenable for both radiofrequency ablation (RFA) and surgery. He was planned for definitive radiotherapy (RT) to the sacral region. During planning CT scan, the skin overlying the lesion was inflamed and impending ulceration, and the patient was unable to lie flat in supine position for adequate immobilization, so he had to be simulated in prone position using four-clamp abdomino-pelvic thermoplastic cast and five mm bolus on the skin overlying the lesion. The RT planned was for 72 Gray (Gy) in 40 fractions, 1.8 Gy daily fractions, five days a week using volumetric modulated arc therapy (VMAT). However, the lesion had clinically appreciable local progression between the simulation and starting of treatment. The local skin appeared even more inflamed, both in intensity and extent, so the RT plan already made had to be aborted and adaptive replanning was considered, with same setup as before. On account of the rapid progression of the primary lesion, an extended planning CT scan covering whole thoracic region was taken. It showed multiple metastatic nodules in both the lungs, the largest being 1.8x1.7 cm in the left upper lobe. With this, the intent of treatment was changed to palliative and the plan for RFA was deferred. He had already received 22Gy in 11 fractions, out of the planned dose. Further palliative intent RT of 12Gy in 2 fractions, 6Gy weekly fractions, was delivered to the local site for palliation of pain. The child has now been receiving symptomatic palliative treatment under the pain and palliative department of our hospital.