skull metastases from thyroid malignancy

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Metastasen des Schädels bei Schilddrüsenkarzinom
skull metastases from thyroid malignancy

Knochenmetastasen bei Schilddrüsenkarzinom

Knochenmetastasen Radiopaedia • CC-by-nc-sa 3.0 • de

Skeletal metastases (a.k.a. bone metastases) are common and result in significant morbidity in patients with metastatic disease. Although the diagnosis is often straightforward, especially as in many cases there is a well-documented history of metastatic malignancy, sometimes they may mimic benign disease or other primary malignancies.

Terminology

It is important to realize that although we commonly talk about bone metastases, strictly-speaking most of these lesions are bone marrow metastases, and metastases originating in the cortical bone itself are much less common . Indeed most of the metastases we see in the cortical bone have directly invaded from the cancellous bone/bone marrow and on x-ray and CT are often not visible until cortical bone involvement has occurred .

Epidemiology

Skeletal metastases account for 70% of all malignant bone tumors, and are seen in a vast number of primary cancers, although lung cancer, breast cancer, renal cell carcinoma and prostate cancer account for approximately 80% of all skeletal metastases . This is due to not only the propensity of these tumors to metastasize to bone, but also the fact that these are some of the most common tumors.

Clinical presentation

The majority of metastases to bone are asymptomatic. Symptoms can arise in a number of scenarios :

  • local bone pain
  • soft tissue mass resulting in:
    • direct compression of adjacent structures by extraosseous soft tissue mass (e.g. cord compression)
    • palpable mass
    • deformity
  • pathological fracture

    • In most cases the diagnosis of metastatic disease is already known. If no known primary exists, or there is uncertainty regarding the diagnosis (e.g. no known metastases; unusual imaging appearances) then a bone biopsy can usually allow definitive diagnosis.

    Laboratory investigations are of limited value, but will often demonstrate increased serum calcium and alkaline phosphatase . Increase in hydroxyproline excretion may also be present .

    Pathology

    The major route of spread of tumor to bone is haematogenous, although lymphatic spread is also seen (e.g. pelvic tumors spreading to para-aortic nodes, and then directly into bone cf. the more common haematogenous spread from the same tumors) . Although direct extension of tumors in bone is also not infrequently seen (e.g. oral cavity tumors into mandible or Pancoast tumors into first rib or upper thoracic vertebrae) this is not usually what is considered metastatic disease .

    Regardless of the route of spread, metastases lead to both bone loss and bone formation, in varying amounts. The former is most likely due to direct enzymatic destruction and osteoclast activation. The latter can be due to stromal bone formation (formation of bone within tumor substrate; the case in prostate cancer metastases) or reactive new bone formation which represents the normal adjacent bone's response to the presence of tumor and is similar to callus formation .

    Distribution

    The distribution of skeletal metastases roughly mirrors the distribution of red marrow, presumably reflecting increased blood flow in red marrow compared to yellow marrow. Thus, metastases are usually found in:

    Metastases distal to the elbow and knee are distinctly uncommon (see distal appendicular skeletal metastases).

    Radiographic features

    Skeletal metastases invariably incite a mixture of bone resorption and bone formation and can thus take on one of three patterns, depending on the dominant process:

  • lytic metastases
  • sclerotic metastases
  • mixed lytic and sclerotic metastases

    • Additionally, metastases can have different morphological characteristics:

    Plain radiograph

    As is the case with other other bone lesions, skeletal metastases can be difficult to identify on plain films since extensive (30-50%) bone mineral loss is required before the density loss is radiographically-visible .

    In many other cases the lesion is visible due to destruction of cortex, or the presence of visible sclerosis.

    It is important to note that unlike primary bone tumors, in general metastases incite no or only limited periosteal reaction. The occasional exception to this general rule includes prostate cancer, some gastrointestinal malignancies, retinoblastoma and neuroblastoma .

    CT

    CT does not have a role in primary assessment for the presence of metastases (except for difficult areas to image such as the spine) but is excellent at defining the extent of bony involvement and in helping assess the risk of pathological fracture.

    MRI

    Whole body MRI is not widely used, but is highly sensitive to replacement of normal bone marrow .

    Nuclear medicine
    Bone scintigraphy

    Bone scans are the most sensitive routine imaging modality to try and identify both sclerotic and lytic lesions . In most cases they demonstrate increased uptake (hot spot) although occasionally (in very aggressive purely lytic lesions) a photopenic defect (cold spot) may be visible. A superscan is also a possible pattern where extensive diffuse metastatic disease results in a uniform increase in uptake .

    Treatment and prognosis

    In general treatment can be thought of as systemic (e.g. chemotherapy or hormonal therapy) or local (e.g. radiotherapy or surgery). Pain management is also often an important part of managing patients with skeletal metastases.

    A rule of thumb is that there is a high-risk of pathological fracture if the lesion is painful, >2.5 cm in size and involves >50% of the bone. There are more formal classification systems, although increasing cortical involvement is probably the most important factor :

    No single statement can be made with regards to the prognosis of patients with skeletal metastases as this will vary greatly depending on the primary tumor.

    Differential diagnosis

    There are, unfortunately, no specific features of metastases, although often the diagnosis is straightforward in the setting of known advanced malignancy and multiple lesions.

    When no history of malignancy is present, but lytic lesions are multiple in an elderly patient, the main differential is multiple myeloma.

    When no helpful features are present (in other words a solitary lesion in an otherwise supposedly well patient) one needs to consider numerous entities:

    • benign and malignant tumor
    • infection
    • trauma
    • osteonecrosis

    The differential can be narrowed according to specific appearances and locations:

    Knochenmetastasen des Schädels Radiopaedia • CC-by-nc-sa 3.0 • de

    Metastases to the skull are very common in patients with disseminated skeletal metastatic disease, although they are often asymptomatic. For a more detailed general discussion please refer to the article on skeletal metastatic disease.

    Epidemiology

    Skull metastases are seen in ~20% (range 15-25%) of all cancer patients . The demographics of patients with skull metastases will mirror those of the primary tumor, and as such in general they are found in the older population.

    Clinical presentation

    Although over half of all skeletal metastases are asymptomatic, they can cause symptoms in a number of scenarios :

    • mass effect on adjacent structures
    • mechanical instability 
      • occipital condyle compression fracture
      • temporomandibular joint instability

    Pathology

    Primary tumors most frequently encountered as metastases to the skull include :

    In children both neuroblastoma (skull metastases are not infrequently the first sign of disease) and Ewing sarcoma are encountered.

    Radiographic features

    Skull metastases have the same range of appearances as skeletal metastases elsewhere, and in 90% of cases other skeletal metastases are evident:

    It is worth remembering that occasionally a solitary skull metastasis may be the only evidence of metastatic disease. This is particularly the case with renal cell carcinoma and thyroid carcinoma .

    Treatment and prognosis

    For asymptomatic lesions, no specific treatment is required above or beyond systemic treatment being administered. Even when symptomatic, in many instances patients are being palliated and as such no focal therapy is instituted.

    In instances where symptoms are significant and the general health and prognosis warrants intervention, a number of options exist :

    • radiotherapy
      • whole brain radiotherapy if cerebral or leptomeningeal metastases are present
      • focal radiotherapy for single/symptomatic lesions
    • chemotherapy
      • usually already instituted for systemic disease
    • surgery
      • reserved for larger symptomatic lesions
      • has a role in diagnosis, when the lesion is solitary or diagnosis not established

    It is difficult to say anything sensible when discussing prognosis, as clearly the degree of systemic disease, and the primary tumor and its response to therapy is going to have a huge impact. In general, it is safe to say however that in most instances, skeletal metastases represent advanced disease with poor prognosis, typically measured in weeks and months.

    Assoziationen und Differentialdiagnosen zu Metastasen des Schädels bei Schilddrüsenkarzinom:
    Knochenmetastasen
    des Schädels
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