25 SUSPECTED METASTATIC DISEASE

Metastasis… synonyms: secondary deposit; deposit

This chapter concentrates on metastases arising from extrathoracic primary neoplasms (i.e. excluding bronchial carcinoma). Many patients with an extrathoracic primary tumour will undergo CXR examination in order to check for metastases. When this CXR examination is requested it is important to know: (a) which tumours are most likely to produce lung, hilar, mediastinal, lymphangitic, pleural or bone deposits; and (b) the various radiographic features of metastatic disease (Fig. 25.1).

image

Figure 25.1 Thoracic metastases: (1) and (2) solitary or multiple; (3) cavitating;(4) cannonball; (5) hilar lymphadenopathy; (6) subcarinal/mediastinal lymphadenopathy;(7) pleural; (8) subpleural; (9) pleural effusion secondary to pleural deposit(s);(10) miliary (resembling millet seeds); (11) lymphangitis carcinomatosa; (12) lytic;(13) sclerotic.

SPREADING AND SEEDING

The precise mechanisms determining whether malignant cells enter the lymphatic or venous circulation and subsequently spread to and implant in the thorax are imperfectly understood1-6. Tumour affinity for a particular thoracic tissue (lung, pleura, bone, bronchial endothelium) varies between malignancies. How some malignancies reach and settle in the thorax is shown in Table 25.1. The various pathways give an inkling as to why some primary tumours metastasise to the thorax more commonly than do others.

Table 25.1 Tumour routes to the thorax1,7–9.

Channel Malignancy Pathway
Lymphatic Breast/stomach/pancreas/larynx/cervix Draining lymphatics → lymph nodes → thoracic duct → vena cava → right atrium → pulmonary arteries → lungs
Venous (1) Renal/thyroid/testicular/sarcomas/melanoma/head and neck Draining veins → vena cava → right atrium → pulmonary arteries → lungs
Venous (2) Colon/stomach/pancreas Draining veins → portal vein → liver → hepatic veins → lungs
Venous (3) Colon/stomach/pancreas Batson’s venous plexus (see below) → bones7,8
Dual venous (4) Renal
(i) Renal vein → inferior vena cava → right atrium → pulmonary arteries → lungs
(ii) Renal vein → Batson’s venous plexus → bones7,8
Multiple Breast1,6,9
image Draining veins → vena cava → right atrium → pulmonary arteries → lungs
image Lymphatics → thoracic duct → vena cava → right atrium → pulmonary arteries → lungs
image Intercostal veins and paravertebral venous plexus → vertebrae → other bones
image Direct invasion → chest wall
image Direct invasion → pleura

Batson’s venous plexus

In 1940 Oscar V. Batson described the vertebral venous system7,8. The term Batson’s venous plexus refers to the valveless plexiform vertebral veins that communicate freely with the superior and inferior vena cavae. This venous system, or plexus, is an important pathway for tumour spread to bone, and also to the brain and lungs.

SEARCHING FOR LUNG METASTASES1,2,9,10

GENERAL

image The basic rule: Whenever possible compare the present CXR with any available previous CXR.
image Deposits are commonly peripheral or subpleural. The lung bases are more frequently affected than are the upper lobes. The majority of deposits are round with fairly well-defined margins.
image Lung deposits immediately adjacent to the pleura (ie subpleural) may not be round. They can appear plaque-like or stellate.

THE PRIMARY TUMOUR AND THE CXR

image Malignancies that commonly metastasise to the lungs: sarcomas, renal cell carcinoma, choriocarcinoma, testicular cancer, some functioning thyroid carcinomas.
image Lung metastases occur relatively infrequently with breast or colon cancer.
image Lung metastases are often present at the time of the initial diagnosis of renal cell carcinoma, choriocarcinoma, Ewing’s sarcoma, osteogenic sarcoma or Wilms’ tumour.
image Other CXR features are listed in Table 25.2.

Table 25.2 Lung metastases1–3,9–12.

CXR finding Most common tumours Other tumours
image More than one deposit and:
image different sizes
image solid appearance
 Kidney, head/neck, uterus, prostate, breast, colon Choriocarcinoma, testicle, melanoma, thyroid, osteogenic sarcoma, Ewing’s sarcoma, Wilms’ tumour, rhabdomyosarcoma
image Solitary lesion
 Colon Melanoma, sarcoma, breast, kidney, bladder, testicle
image Cannonball (i.e. very large)
 Colon, rectum, kidney, melanoma, sarcomas  
image Cavitation9
 Cervix in females, head and neck tumours in males, sarcomas Colon
image Miliary pattern
 Thyroid, kidney Osteogenic sarcoma, melanoma, choriocarcinoma
image Calcified9,13
 Osteogenic sarcomas Chondrosarcoma, thyroid, colon, pancreas
image Margins very ill-defined
 Choriocarcinoma… occasionally2  
image

Figure 25.2 Typical appearance and individual features of lung metastases: multiple lesions, variable size, well-defined margins. Testicular tumour.

image

Figure 25.3 Miliary metastases…multiple tiny secondary deposits. Thyroid carcinoma.

image

Figure 25.4 Cavitating metastasis (arrow). Tough to detect because it lies below the horizon of the dome of the diaphragm. Remember…you only see what you look for.

SEARCHING FOR HILAR AND MEDIASTINAL METASTASES

image The appearances of hilar lymph node enlargement are described on pp. 76–77.
image Extrathoracic tumours infrequently metastasise to mediastinal lymph nodes. If mediastinal lymphadenopathy is evident consider these tumours:
image bronchial carcinoma
image lymphoma
image kidney, testicle, head and neck
image

Figure 25.5 Patient with weight loss. Paratracheal lymphadenopathy (white arrow). When enlarged mediastinal nodes are due to malignancy it is rare for the primary tumour to be extrathoracic. The most common primary tumour will be a bronchial carcinoma (black arrow).

LYMPHANGITIS CARCINOMATOSA1,2

Tumour involvement of the lymphatics of the lung results from haematogenous spread. The CXR appearance is that of interstitial disease—i.e. reticular or reticulo-nodular shadowing. Initially, this may be indistinguishable from other interstitial processes such as pulmonary oedema. The most common primary is breast carcinoma.

image Lymphangitic spread is usually bilateral, infrequently unilateral. Sometimes it is associated with a pleural effusion and/or enlarged hilar nodes.
image Very occasionally a patient with a known primary carcinoma may develop dyspnoea due to lymphangitic deposits and the CXR may appear clear1.
image Useful rule of thumb: If an interstitial pattern is due to lymphangitis carcinomatosa then the patient will be short of breath.
image

Figure 25.6 Lymphangitis carcinomatosa. The reticular shadowing at the right base is fairly typical of the pattern of tumour involving the lymphatics. The primary tumour was a breast carcinoma.

SEARCHING FOR PLEURAL METASTASES14

Some cancers have a predilection for the pleura.

image The CXR may show:
image a pleural effusion, small or large
image an isolated pleural mass
image The most common primary tumours:
image any adenocarcinoma, including bronchus
image breast carcinoma
image

Figure 25.7 Left pleural effusion. An effusion is the most common CXR finding in a patient who has metastatic disease involving the pleura. This patient had a previous carcinoma of the breast and a right mastectomy.

SEARCHING FOR BONE METASTASES3,8,9,15

image Some primary tumours have a propensity for metastasising to bone (Table 25.3). Other tumours rarely do so.
image Bone metastases occur as a result of either: (a) tumour cells entering the venous system and being deposited in bone via arteries and capillaries;(b) retrograde venous flow (e.g. prostatic carcinoma); (c) dissemination via Batson’s venous plexus; or (d) direct invasion of adjacent bone.
image Bone deposits are usually either solely lytic (i.e. lucent) or solely sclerotic (i.e. dense)—see Table 25.3. Very occasionally a primary carcinoma may produce both lytic and sclerotic deposits in an individual patient.
image A helpful trick. Any patient with bone or chest wall pain. When checking the ribs:
image Rotate the image so that the long axis of the CXR is parallel to the floor—assess the ribs again (Fig. 25.8).
image Then rotate the CXR through another 90° so that the CXR is upside down—assess the posterior aspects of the ribs again.

Table 25.3 Bone metastases15.

Appearance Most common primary Less common primary
Sclerotic
image Males—prostate
image Females—breast
Pancreas, bladder, carcinoid, mucinous adenocarcinomas of the gastrointestinal tract
Occasionally lymphoma
Lytic
image Males—bronchus, kidney, thyroid
image Females—breast, kidney, thyroid
 Prostate, melanoma, neuroblastoma
Lytic…sometimes causing expansion of the affected bone Renal, thyroid  
image

Figure 25.8 Checking the ribs for metastases. Examining the ribs with the CXR aligned horizontally. This trick makes the ribs stand out. Note the destructive lesion in the posterior aspect of the left fifth rib. If you don’t think that the lesion is shown particularly clearly— turn this page through 90° so that you are looking at the bones with the CXR upside down. Now what do you think?

image

Figure 25.9 A destructive (lytic) metastasis in the posterior aspect of the left fifth rib.

image

Figure 25.10 Sclerotic right sixth rib posteriorly. Metastasis from a prostatic carcinoma. Several other ribs showed a similar appearance.

AN UNEXPECTED RIB FRACTURE—IS IT PATHOLOGICAL?15-17

Most pathological fractures are due to a metastasis or to myeloma. Whenever a clinically unsuspected rib fracture is detected on a CXR:

1. Always link the fracture to the patient’s present or past clinical history.
2. Look for other rib lesions.
3. Analyse the appearance carefully:
image Bone sclerosis. Two possibilities: a metastasis or callus around a healing simple fracture.
image Bone lucency—i.e. destruction. Consider metastasis or myeloma. Very rarely—lymphoma.
image Bone expansion. More commonly myeloma than a metastasis.
image Adjacent soft tissue extrapleural mass. More common with myeloma.
4. If carcinoma is considered to be a possibility then obtain an isotope bone scan. If the rib lesion is a secondary deposit then there will be multiple other deposits shown elsewhere in the skeleton.
5. If myeloma is likely then a myeloma haematological screen is necessary. If positive this should be followed by a radiographic skeletal survey. An isotope bone scan is often normal in myeloma because there is minimal or no bone turnover at the site of the lesion and consequently no increase in tracer uptake.
image

Figure 25.11 Destructive lesion in the posterior aspect of the left seventh rib. The differential diagnosis is metastasis or myeloma. The prominent accompanying soft tissue shadow does favour myeloma. Myeloma was the diagnosis in this patient.

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