Benign nodules can grow slowly[9,11].
Except one case had sclerosing hemangioma grown slowly (with a doubling time of 1697 days),
3 cases had solid nodules,
1 case had pure ground-glass opacity nodule with a doubling time same as that of lung cancer.
Literatures[12] have recorded that the doubling time of lung cancer is generally <400 days [mean: 149 days[13] and range: 20-400 days[14].
Only upon the doubling time,
the growing nodules in 4 cases are likely to be misdiagnosed as lung cancers.
Besides the doubling time,
spiculation and lobulation on the nodule margin are the most important morphological characteristics of malignant lesions.
In this article,
2 cases were found with tuberculoma.
Case 1 had enlarged nodule during follow-up visits with spiculation on the margin,
which further increased the probability of malignant lesion.
Case 2 were found to have obviously enlarged nodule at the 5th examination with the maximum diameter of up to 2.7cm and slightly irregular margin,
which were suspected of scar cancer.
But the satellite lesions around the nodule and net enhancement value of pulmonary nodule being ≤15HU were considered as important features of benign lesions[15].
These 2 cases had satellite lesions around the nodules,
which were present all the time in Case 2 but as the tree-in-bud sign at the 3rd reexamination with CT scan in Case 1.
When both cases had enlarged tuberculoma,
enhanced CT scan showed insignificant nodular enhancement and the net enhancement value of <15HU.
Case 1 was present with contradictory reaction (or known as transient worsening) during anti-tuberculosis treatment[16],
which generally occurred within 1-3 months of anti-tuberculosis treatment.
As treatment continued,
lesions were finally shrunk after absorption.
Contradictory reactions present in cases of tuberculoma were seldomly reported,
which might be associated with focal necrosis and edema( Case 1: Fig. 1 ,
Fig. 2 ,
Fig. 3 ,
Fig. 4 ,
Fig. 5 ).
Case 3 had fungal infection with progressively enlarged nodules.
It was found at the 3rd reexamination that there were spiculation on the margin besides obvious enlargement,
which were highly suspected of malignant nodules with multiple metastases of the right lower lobe.
After surgical resection,
the nodule was confirmed with Cryptococcus neoformans infection.
After antifungal treatment,
secondary absorption and disappearance of nodules occurred in the right lower lobe.
During reviewing,
the first CT scan showed that the nodule with fungal infection was located at the junction between the dorsal segment and basal segment of the right lower lobe,
the second reexamination showed new onset of one small nodule near the bronchial opening at the dorsal segment of the lower lobe above and at the basal segment of the right lower lobe below respectively,
and the third reexamination also showed multiple densely packed small nodules near the nodule and adjacent to its bottom.
MacMahon and Fleischner Society[17] believes that the cluster of multiple nodules in a single site in the lung often suggests an infectious process.
The surrounding of some small nodules showed the typical halo sign,
which also suggested infection,
especially fungal infection[18](Case 3: Fig. 6,
Fig. 7,
Fig. 8, Fig. 9 ).
Case 5 was pathologically diagnosed with sclerosing pneumocytoma (sclerosing hemangioma) after surgery.
Both the morphology and the doubling time suggested that the sclerosing pneumocytoma was a benign lesion.
After enlargement,
the halo sign and mild lobulation occurred on the margin.
The observed irregular tumor margin and surrounding halo sign reported in the literatures are pathologically confirmed as tumor infiltration into the surrounding tissue and intra-alveolar bleeding respectively[19].
Nodular enlargement suggests that the lesion is active[17].
Whether enlarged tumor with 2 signs in this case indicated active tumor growth and needed prompt removal should be observed further.
The case was found with no lymph node metastasis.
Case 4 was pathologically diagnosed with granulomatous inflammation after surgery.
This case was characterized by the image of a large pure ground-glass opacity nodule with a diameter of about 3 cm in rapid growth.
The nodular doubling time was 255 days,
consistent with that of lung cancer.
The mean doubling time of adenocarcinoma with pure ground-glass opacity in the lung was 813 days[13].
The nodule was surrounded by lacelike high-density shadow,
i.e.,
reversed halo sign.
Reversed halo sign can be seen in infectious or non-infectious lesions and tumor lesions[20].
Due to further enlargement found in reexamination,
the nodule was highly suspected of a malignant lesion and resected after being pathologically diagnosed as a granulomatous lesion.
All these suggested that pure ground-glass opacity nodule grown rapidly may also be benign(Case 4: Fig. 10,
Fig. 11,
Fig. 12 ).
In conclusion,Although some benign pulmonary nodules appeared to show the growth characteristics similar to malignant tumors,
they also had some signs contradictory to malignant tumors,
such as the satellite lesions,
net enhancement value of ≤15HU,
multiple nodules in a single location,
grown slowly and halo sign.
Imaging doctors should observe and analyze these contradictions carefully to minimize misdiagnosis.
Funding
This study has received funding by grants from Scientific Research Funding of Hainan Province (No.
ZDYF2017106) of China.