The combination of endoscopy and ultrasonography in one tool produces better results in the diagnosing and staging cancer
By Dr Lee Yuk Tong
Specialist in Gastroenterology & Hepatology, Hong Kong Adventist Hospital
Gastrointestinal and lung cancer are among the most commonly encountered cancer diseases in Hong Kong accounting for around half of the 25,977 new cancer cases and two third of all cancer deaths in 2009, according to the Hong Kong Cancer Registry.
Diagnosis of these cancers usually involves obtaining tissues from the tumour sites for pathological examination. Endoscopy, including gastroscopy, colonoscopy and bronchoscopy, are frequently used for such a purpose.
However, the endoscopic examination and biopsy method of diagnosis does have its limitations especially if the tumour is not within the reach of the endoscope, or is infiltrating below the surface of the mucosa, or has spread to the surrounding lymph nodes. In these cases, ordinary endoscopic methods often fail to properly assess the diseases extent and obtain adequate tissue to make an accurate diagnosis and staging of the cancer.
Recent advances in radiological imaging techniques, such as the high-speed CT scan and positron emission tomography (PET scan), have put new diagnostic tools into the hands of cancer specialists; however, these cannot replace tissue diagnosis when planning treatment.
Getting the diagnosis right
The consequence of a wrong tumour diagnosis and staging may result in the patient receiving inappropriate invasive surgery and oncological treatment, and the inherent treatment related complications.
Endoscopic ultrasonography (EUS) was developed more than 30 years ago and has become an important tool in the diagnosis and staging of cancer.
It involves using either a specifically designed endoscope equipped with an ultrasound at the tip, or a miniature ultrasound probe that can pass through the working channel of an ordinary endoscope to perform the examination.
When the endoscope is inserted into patientís gastrointestinal tract or bronchus, both luminal and extraluminal (inside and outside) structures can be examined in great detail.
High sensitivity improves detection
The high frequency ultrasound probe used with EUS has been shown to have the highest sensitivity in detecting the presence of a gastrointestinal submucosal tumour (frequently being seen as a lump and bump in the gastrointestinal wall), pancreatic and bile duct cancers, and mediastinal lymph node metastases in patients suffering from lung cancer diseases.
In addition, a EUS-guided biopsy through the gastrointestinal track or bronchus also allows the endoscopist to take tissue from sites which are inaccessible to ordinary endoscopic methods. In doing so, a more accurate diagnosis of cancer and assessment of the stage of the cancer are possible.
In the case of lung cancer, both the American and European cancer societies now recommend using EUS to obtain tissue diagnosis from suspicious mediastinal lymph node before embarking on thoracic surgery. This is because direct surgery is not appropriate if cancer has spread to the mediastinal lymph node. If it has spread, patients should undergo chemotherapy or radiotherapy before surgery to improve their chance of survival.
Seeking out small and early stagecancers
EUS have also been shown to be more sensitive than conventional CT scan and PET scan in detecting the presence of pancreatic cancer and neuroendocrine tumours, especially when the tumour is very small and in an early stage.
New ultrasound contrast agents, used together with the latest EUS machine, have been shown to further improve the diagnosis of various pancreatic tumour diseases and chronic pancreatitis.
This is why EUS has been used in some studies to screen high risk patients, such as patients with strong family history of pancreatic cancer disease or with certain genetic predispositions. EUS can also be used for patients with persistent upper abdominal pain to rule out underlying pancreatic lesion when other tests are negative.
EUS also help in patients with radiologically inoperable pancreatic cancer disease by providing tissue diagnosis to confirm the cancer type before oncological treatment. For patients with intractable pain related to late stage pancreatic cancer disease, EUS-guided nerve destructive treatment can alleviate pain and reduce the need for painkillers.
All these advantages make EUS an invaluable tool in diagnosing and staging certain cancers. However, as with all similar procedures, the success of this type of examination is dependent on the examinerís experience in accurate image interpretation and guided treatment.