A Solitary Pulmonary Micronodule in Melanoma Staging – Metastasis?

Sascha Daniel, MD; Matthias May, MD
Department of Radiology, University Hospital Erlangen, Erlangen, Germany
 |  2019-12-03

History

A 38-year-old male patient had undergone resection of a melanoma found on his upper left chest. Prior to surgery, he was asymptomatic and a chest X-ray in two planes was required for primary staging. An ultra-low-dose native CT scan was performed instead, with patient consent, and a solitary pulmonary micronodule, 1 mm in diameter, was visualized in the right upper lobe. No lymphonodal or distant organ metastases were found. 16 months later, the patient returned for a follow-up and an ultra-low-dose native CT examination was once again performed.

Diagnosis

In comparison to the prior examination, CT images showed no changes of the solitary pulmonary micronodule in the right upper lobe. The micronodule was therefore characterized as a small post-infection scar and thus non-malignant. No pulmonary metastases or enlarged lymph nodes were seen in either the axillae or the mediastinum. The resection scar on the upper left chest was no longer visible and there were no other suspicious cutaneous lesions.

Fig. 1: Axial images demonstrate no changes in a micronodule (arrows) in the right upper lobe when comparing the primary staging (Fig. 1b) to the follow-up exam (Fig. 1a).

Fig. 2: Axial (Fig. 2a) and coronal (Fig. 2b) views of MIP images (22 mm thickness) show the unchanged micronodule (arrows) in the follow-up exam.

Comments

A melanoma is a malignant skin cancer deriving from the pigment-containing melanocytes. The increasing incidence rate[1] demands a staging tool that can detect even small lesions and which is also cost-efficient and has a positive risk-benefit-ratio.[2] The radiation exposure level of a standard posteroanterior and lateral chest X-ray is in average 0.1 mSv.[3] This is similar to that of an ultra-low-dose CT.[4] The reduction in exposure is enabled by an advanced tin filter technology, which optimizes the X-ray spectra and significantly improves the air / tissue contrast. In this case, using SOMATOM go.Top, a pulmonary micronodule with a diameter of only 1 mm is visualized at an effective dose level of 0.17 mSv in primary staging. In the follow-up evaluation, the effective dose level is further reduced to 0.11 mSv using SOMATOM X.cite. Lymph nodes in the axillae and mediastinum could also be evaluated, which is not possible on a regular chest X-ray examination.

Examination Protocol

ScannerSOMATOM go.TopSOMATOM X.cite
Scan areaThoraxThorax
Scan modeSpiral scanSpiral scan
Scan length328 mm325 mm
Scan directionCranio-caudalCranio-caudal
Scan time1.8 s3.1 s
Tube voltageSn110 kVSn140 kV
Effective mAs35 mAs6 mAs
Dose modulationCARE Dose4DCARE Dose4D
CTDIvol0.30 mGy0.24 mGy
DLP12 mGy cm8 mGy cm
Effective dose0.17 mSv0.11 mSv
Rotation time0.33 s0.3 s
Pitch1.20.8
Slice collimation64 x 0.6 mm64 x 0.6 mm
Slice width1 mm0.8 mm
Reconstruction increment0.7 mm0.6 mm
Reconstruction kernelBr60f (ADMIRE3)Br60f (ADMIRE3)

[1] Rastrelli M, Tropea S, Rossi CR, Alaibac M. Melanoma: epidemiology, risk factors, pathogenesis, diagnosis and classification. In Vivo. 2014; 28:1005–1011

[2] Dinnes J, Ferrante di Ruffano L, Takwoingi Y, Cheung ST, Nathan P,Matin RN, Chuchu N, Chan SA, Durack A, Bayliss SE, Gulati A, PatelL,Davenport C, Godfrey K, Subesinghe M, Traill Z, Deeks JJ, Williams HC, Cochrane Skin Cancer Diagnostic Test Accuracy Group. Ultrasound, CT, MRI, or PET-CT for staging and re-staging of adults with cutaneous melanoma. Cochrane Database of Systematic Reviews 2019, Issue 7. Art. No.: CD012806.

[3] Mettler Jr FA, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology. 2008; 248(1):254–63.

[4] Messerli M, Kluckert T, Knitel M, Wälti S, Desbiolles L, Rengier F, et al. Ultralow
dose CT for pulmonary nodule detection with chest x-ray equivalent dose - a prospective intra-individual comparative study. Eur Radiol. 2017;1–10.

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