“Miliary lung parenchymal opacities” as presenting feature of metastatic papillary type of thyroid malignancy: It’s not tuberculosis always!

High-resolution computed tomography thorax

1. Bilateral lung parenchymal nodular opacities, denser in the middle lobe, lingual, and both lower lobes as compared to the upper lobes [Figures 2 and 3]

2. Characteristically, these nodules are of variable size ranging from 3 mm to 8 mm, randomly distributed, bizarre shape, showing contrast uptake, and with interstitial enhancement favoring lymphohematogenous dissemination [Figures 2 and 3]

3. Multiple opacities are larger in size to label miliary mottling and showing craniocaudal discordance with conglomeration with contrast enhancement to favor non-tuberculous pathology [Figures 2 and 3]

4. Nodular opacities with an irregular shape, accompanied by conglomeration with parenchymal distortion in bilateral lower lobes without pleural or pericardial involvement [Figures 2 and 3].

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Figure 2:

High-resolution computed tomography thorax showing multiple, bilateral nodular opacities with craniocaudal discordance and conglomeration.

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Figure 3:

High-resolution computed tomography thorax showing miliary nodule with conglomeration and parenchymal distortion in bilateral lower lobes with interstitial involvement.

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CT neck

1. Bulky right lobe of the thyroid with hypodense thyroid nodule of size 2 cm × 1.7 cm noted in the right lobe with calcification and mild heterogeneous enhancement on contrast study mostly favors malignant pathology [Figure 4]

2. Multiple enlarged lymph nodes are seen at the bilateral jugular, submandibular, and right paratracheal region largest of size 23 mm × 17 mm at the right middle jugular region [Figure 4a-b].

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Figure 4:

(a and b) Computed tomography neck showing bulky right lobe of thyroid with hypodense thyroid nodule in the right lobe with calcification.

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Percutaneous thyroid cytology smears show sheets and papillae like structures of follicular cells with well-defined anatomical border. The cells show powdery chromatin, nuclear grooves, intranuclear pseudo inclusions, and nuclear overlapping. Cytology analysis confirmed papillary type of thyroid carcinoma with Bethesda category VI.

We have referred this case to the tumor board of our institute after clinical parameter stability and general health improvement during hospitalization. In the tumor board panel, a multidisciplinary team of surgical oncologist, radiation oncologist, and medical oncologist decided on surgical removal of the thyroid with radioactive iodine therapy after surgery.

Miliary opacities due to tuberculosis and miliary metastasis: how to differentiate?

1. Size of nodules: Size <1.5 mm was more common in TB than malignancy. Nodule size of more than 3 mm was more frequently reported in miliary metastasis than TB. Nodule size between 1.5 mm and 3.0 mm is documented in miliary metastasis and TB in equal frequency^[13]

2. Diversity in size of nodules: Variation in size of nodules is more frequently reported in miliary metastasis than miliary TB

3. Well-defined margins of nodules: Well-defined margins are commonly documented in TB and miliary metastasis. Ill-defined margins are a feature of metastasis than TB

4. Distributions as lower zone predominance or even distribution: Predominant lower zone is a typical feature of metastatic (70% cases) than miliary TB (30%). Even distribution of nodules is seen in miliary TB, that is, involvement of all zones equally. Even distribution is not common in miliary metastasis^[14]

5. Coalescence or conglomeration: Common in miliary TB and miliary metastasis

6. Interstitial involvement is typically described as interlobular septal thickening or peribronchovascular thickening: Interstitial involvement is common in miliary metastasis and infrequently reported in TB

7. Ground-glass opacity: Common in TB and metastasis

8. Pleural effusion: Common in TB and metastasis

9. Lymph node enlargement: Common in TB and metastasis.

Papillary thyroid carcinoma (PTC) is the most frequent type with a ratio of 80%. PTC commonly metastasizes to regional lymph nodes. However, distant metastasis may rarely occur and accounts for 5% of the patients. The lungs and the bones are the most common sites for distant metastasis. Major risk factors for PTC include radiation exposure, insufficient or excess dietary iodine, Cowden’s disease, Gardner’s syndrome, and dyshormonogenetic goiter.^[15]

Learning points

1. Constitutional symptoms with miliary opacities are more frequently reported in pulmonary TB. Miliary opacities are also observed in infectious, inflammatory, neoplastic, and interstitial lung diseases.

2. Conventional chest radiograph is a less sensitive technique to differentiate etiological factors for miliary TB as fine details of miliary opacities could not be possible and usually underestimated other causes for the same.

3. Although microbiological workup is indicated and must for diagnosis of TB, it is usually negative due to less or negligible expectoration in miliary TB. Induced sputum examination is superior to conventional sputum examination in miliary TB but less sensitive to bronchoscopy-guided samplings.

4. Empirical ATT with case definition as “X-ray-positive” without microbiological evidence and atypical radiological opacities and constitutional symptoms is always dangerous and should be phased out.

5. We recommend that etiological factors for miliary opacities should be actively sought, which will have an impact on the final outcome. Miliary TB is a common cause in India, and malignancy is not uncommon. Fine-needle aspiration is reliable, sensitive, and bedside test to diagnose thyroid neoplasms. Thus, we quote the slogan for miliary opacities as “It is not TB always for miliary opacities!”