Firstly, we need to frame the condition we are evaluating within one of the five major chapters of Pathology:

             1- CONGENITAL MALFORMATIONS

             2- CIRCULATORY DISORDERS

             3- DEGENERATIVE PROCESSES

             4- INFLAMMATORY

             5-  NEOPLASTICS

          If the case was classified within the neoplasms chapter, our objective is to establish the diagnosis so that we can institute treatment. It is essential to establish an accurate diagnosis.

          To be diagnosed, it is necessary to know and learn the universe of tumors already described.

          Are we, as medical students, not already aware of all musculoskeletal neoplasms?

          We usually convey, in our classes, that our brain can store information randomly. However, if when we assimilate knowledge we try to do it in an orderly way, it will be “stored” in “folders”, these in “drawers” ​​and we will have a “ file ” . This way we can retrieve the information more easily.

          We will therefore help you build this  file,  organizing the  “HD” .

          Firstly, we need to remember that the neoplasm originates from a cell that already exists in our body. This cell, when reproducing, undergoes changes in its genetic code, due to different factors (radiation, viruses, mutations, translocations, etc.) and this then becomes the “ mother cell ” of the neoplasm.

          As we already learned histology at the Faculty, we are knowledgeable about all possible neoplasms. We just need to add some concepts to safely name and classify all the tumors already described.

The term carcinoma          was reserved  for malignant neoplasms whose primitive cells originate from the ectodermal layer and  sarcoma  for those from the mesoderm. 

          If we take our thigh as an example and do an exercise, remembering all the cells that make it up, starting with the skin and going deeper into the subcutaneous tissue, muscles, etc., up to the bone marrow of the femur, we will have reviewed all the cells of the locomotor system. and therefore we will be able to name all musculoskeletal neoplasms.

          Let’s do this exercise. Starting with the skin, we remember  squamous cell carcinoma ,  basal cell carcinoma  and  melanoma . These neoplasms are most frequently treated by dermatologists and plastic surgeons and only rarely require the help of an orthopedist.

          Below the skin, all structures are derived from the mesoderm and therefore we will add the suffix  oma for benign  lesions   and  sarcoma  for  malignant ones .

          Therefore, below the skin we have the subcutaneous cellular tissue (fat) whose most representative cell is the lipocyte. If the lesion is made up of cells similar to the typical lipocyte, we will have a  lipoma , consisting of disordered cells, with atypical mitoses, a  liposarcoma . In this same subcutaneous tissue we have fibroblasts, fibrohistiocytes and consequently  fibroma ,  fibrosarcoma ,  fibrohistiocytoma  of low and high degree of malignancy.

          Another structure that makes up our thigh are the striated muscles, (voluntary muscles), thus giving rise to  rhabdomyosarcoma . Smooth muscles, found in the locomotor system, are located around the vessels and, although they are rare, we also find  leiomyosarcoma .

          Nervous tissue is represented here by the axons of peripheral nerves. These axons have a sheath, whose cells were described by Schwann, from which  Schwannoma can originate .

           In soft tissues, remembering, as derived from lymphatic tissue,  lymphangioma  and  lymphangiosarcoma ; vascular tissue,  hemangioma  and  angiosarcoma .

          The bone is covered by the periosteum, whose function is to form bone tissue, in addition to protecting, innervating and nourishing. Trauma can lead to the formation of a sub-periosteal hematoma which, if mature, homogeneous ossification occurs, can be translated as a  periosteoma  (“osteoma”). Low-grade surface osteosarcoma  known as  paraosteal osteosarcoma  (grade I) as well as high-grade osteosarcoma can be derived from this same bone surface  .

          In our exercise we now reach the medullary region of the bone. This region is made up of fat, which can then lead to  intraosseous liposarcoma  and red bone marrow, from which we can have all neoplasms of the ERS ( Reticulum Endothelial System ) such as  plasma cell myeloma ,  lymphocytic lymphoma ,  Ewing’s sarcoma .

          If we remember, deep in our memory, the histology of endochondral ossification, we will find several precursor cells. One of them is large  (giant)  made up of cells with several nuclei, responsible for bone resorption, the osteoclast and consequently we have  osteoclastoma , better known as  giant cell tumor  ( GCT ). From the chondroblast the  chondroblastoma ; osteoblast  , osteoblastoma ; from the chondrocyte the  chondroma , the  chondrosarcoma ; and so on, we will be able to deduce all the neoplasms described. It will be enough to name them based on the knowledge of the normal cell, adding  oma  to the benign lesion and  sarcoma  to the malignant one.

          We consider this form of introduction to be important, as this way we will be better helped to remember what we already know and arrive at the diagnosis.

          The World Health Organization groups these injuries according to the tissue they try to reproduce, classifying them into:

I –  Tumors that form bone tissue

       Benign:  Osteoma – Osteoid Osteoma – Osteoblastoma

       Intermediate :  Aggressive Osteoblastoma

       Malignant :  Central Osteosarcoma – Parosteal – Periosteal – High Grade

II –  Cartilage-forming tumors

       Benign :  Chondroma (enchondroma) – Osteochondroma – Chondroblastoma – Chondromyxoid Fibroma

       Malignant :  Primary – Secondary – Juxtacortical – Mesenchymal – Dedifferentiated – Clear Cell Chondrosarcoma

III –  Giant Cell Tumors   (GCT) (Osteoclastoma)

IV –  Bone Marrow Tumors

         Malignant :  Ewing Sarcoma – Lymphocytic Lymphoma – Plasmocyte Myeloma – PNET

V –  Vascular Tumors

        Benign :  Hemangioma – Lymphangioma – Glomus tumor

        Intermediate :  Hemangioendothelioma – Hemangiopericytoma

       Malignant :  Angiosarcoma

VI –  Connective Tissue Tumors

         Benign :  Fibroma – Lipoma – Fibrohistiocytoma

         Malignant :  Fibrosarcoma – Liposarcoma – Malignant fibrohistiocytoma – Leiomyosarcoma – Undifferentiated sarcoma

VII –  Other tumors

           Benign :  Schwannoma – Neurofibroma

           Malignant :  Chordoma – Adamantinoma of the long bones

VIII –  Metastatic Tumors in the Bone

            Carcinomas: breast, prostate, lung, thyroid, kidney, neuroblastoma, melanoma, etc.

IX –  Pseudotumor Lesions

         Simple bone cyst (COS)

         Aneurysmal bone cyst (AOC)

         Juxta-articular bone cyst (intraosseous ganglion)

         Metaphyseal fibrous defect (Non-ossifying fibroma)

         Fibrous dysplasia

         Eosinophilic granuloma

        “Myositis ossificans”

        Brown tumor of hyperparathyroidism

        Intraosseous epidermoid cyst

        Giant cell reparative granuloma

         All of these lesions mentioned have  clinical particularities ,  imaging characteristics , and  histological aspects  that need to be analyzed together to correlate each one of them.

         This is fundamental, as we can have radiologically and/or histologically similar lesions but with different diagnoses.

         Therefore, imaging studies and histology must always be correlated with the clinical picture, for the correct diagnosis.