title: Popliteal lymph node metastasis of tibial osteoblastic osteosarcoma.
abstract: BACKGROUND
  We report a case with lymph node metastasis of osteosarcoma, which is a rare entity in comparison to hematogeneous lung or bone metastasis.
  
  
  METHODS
  Twenty-seven years old male patient referred to our clinic complaining of ongoing left knee pain and swelling since one month without a history of prior trauma. Magnetic resonance imaging (MRI) revealed a mass of malignant nature which causes more prominent expansion and destruction of the bone distally with periosteal reaction. A lymphadenomegaly 16mm×13mm in diameter was also present in the popliteal fossa having the same signal pattern with the primary lesion. Thirteen weeks following the first referral of the patient, wide resection and reconstruction with modular tumor prosthesis was performed. Popliteal lymph node was excised through the same incision. Pathologic examination of the resected speciman reported osteoblastic osteosarcoma. The lymph node extirpated from the popliteal fossa was reported to be a metastasis of the primary tumor.
  
  
  CONCLUSIONS
  Osteosarcoma of the long bones is the most common primary malignant bone neoplasm of both childhood and adulthood. Osteosarcomas commonly metastasize hematogeneously to the lungs and bones. Lymph node metastasis is a rare entity. Similar studies report rates between 2.3% and 4%. It is not clearly explained, how lymph node metastasis in osteosarcoma occurs despite lack of lymphatic drainage in normal cortical and spongious bone.
  
  
  CONCLUSIONS
  Lymph node metastasis of osteosarcoma is a rare entity and metastatic patterns could not be clearly explained. On the other hand, the effects of lymph node metastasis on prognosis are also not clearly defined and further studies are needed.
authors.affiliation: Memorial Şişli Hospital, Orthopaedics and Traumatology, Piyalepaşa Bulv., Okmeydanı, Şişli, 34385 İstanbul, Turkey. Electronic address: drdirik@gmail.com.
authors.forename: Yalın
authors.initials: Y
authors.lastname: Dirik
authors.affiliation: Memorial Şişli Hospital, Orthopaedics and Traumatology, Piyalepaşa Bulv., Okmeydanı, Şişli, 34385 İstanbul, Turkey. Electronic address: arda.cinar@memorial.com.tr.
authors.forename: Arda
authors.initials: A
authors.lastname: Çınar
authors.affiliation: Memorial Şişli Hospital, Orthopaedics and Traumatology, Piyalepaşa Bulv., Okmeydanı, Şişli, 34385 İstanbul, Turkey. Electronic address: feridun.yumrukcal@memorial.com.tr.
authors.forename: Feridun
authors.initials: F
authors.lastname: Yumrukçal
authors.affiliation: Istanbul University, Istanbul School of Medicine Orthopaedics and Traumatology, Turgut Özal Millet Caddesi, Çapa Tıp Fakültesi, Çapa - Cerrahpaşa, Fatih, Pk: 34098 İstanbul, Turkey. Electronic address: drleventeralp@gmail.com.
authors.forename: Levent
authors.initials: L
authors.lastname: Eralp
keywords: Lymph node metastasis; Osteoblastic osteosarkoma; Osteosarcoma; Tumor