Eggshell calcification

CASE SUMMARY

A 27-year-old nonsmoker male working in a stone cutting factory for 2 years presented to the hospital with complaints of breathlessness, chest pain, and cough with minimal sputum. There was no fever, loss of weight, or appetite. He had received antitubercular therapy three times in the past on the basis of symptoms and chest radiograph lesions although acid-fast bacilli were never found on direct smear or culture. General physical examination was not remarkable except for tachypnea, and chest examination revealed bilateral infraclavicular and suprascapular inspiratory and expiratory crackles and generalized polyphonic expiratory wheeze. Lung function tests revealed severe restrictive ventilatory defect with diffusion capacity impairment (forced vital capacity [FVC] 40% of predicted, forced expiratory volume in 1 s [FEV1] 36% of predicted, FEV1/FVC 77% of predicted, total lung capacity 50% of predicted, and DLCO 45% of predicted). A chest radiograph (posteroanterior [PA] view) was obtained [Figure 1] followed by high-resolution computed tomogram (HRCT) of the chest [Figures 2 and 3].

Figure 1: Chest radiograph (posteroanterior view)

Figure 2: High-resolution computed tomogram of the chest (mediastinal window) at the level just below the carina. Description in answer 2

Figure 3: High-resolution computed tomogram of the chest (lung window) at the level just below the carina. Description in answer 2

QUESTIONS

1. Question 1: What are the observations on the chest radiograph?
2. Question 2: What does the HRCT of the chest show?
3. Question 3: What is the diagnosis?

ANSWERS

1. Answer 1: The chest radiograph (PA view) [Figure 1] shows bilateral upper and midzone dense fibrocavitary lesions with interspersed calcified nodular opacities and compensatory hyperinflation in the lower zones
2. Answer 2: HRCT of the chest [Figures 2 and 3] shows bilateral upper lobe dense fibrotic lesions representing progressive massive fibrosis (shown by arrow) with cavitation and calcified nodular opacities. In addition, the mediastinal (subcarinal) and bilateral hilar lymph nodes are calcified. The pattern of calcification is the classical “eggshell calcification,” a calcified rim around the periphery of the lymph nodes (shown by arrow)
3. Answer 3: Chronic silicosis.

DISCUSSION

Silicosis is a fibrotic pneumoconiosis that follows exposure to various forms of free crystalline silicon dioxide or silica generated during cutting and blasting of granite, slate, and sandstone[¹] and is well documented in India.[²] Depending on the nature and duration of exposure and clinical presentation, it may manifest as acute, accelerated, or chronic forms. The main symptom of the patients is usually exertional breathlessness although cough with sputum is also common. Silicosis also increases the risk of tuberculosis by 2–30 times, besides being associated with lung cancer and systemic sclerosis.[³⁴] Lung function testing reveals a mixed obstructive-cum-restrictive pattern in the majority of patients.[⁴] Spontaneous pneumothorax, rarely bilateral, may complicate silicosis.[⁵] Diagnosis is established by occupation history, clinical presentation, and chest imaging features.

The radiological lesions on plain radiography and HRCT scans of the chest include multiple small nodules scattered diffusely throughout the lungs with upper zone predilection. Calcification may occur, and coalescence of nodules and fibrosis leads to the formation of bilateral upper lobe masses, a picture labeled as “progressive massive fibrosis.” These opacities have ill-defined margins, are more than 1 cm in size, and often bilaterally symmetrical with lateral interfaces of the lesion parallel to lateral chest wall.[³⁶] Cavitation secondary to ischemic necrosis may occur. Hilar and mediastinal lymphadenopathy is common, and the lymph nodes may show calcification. Eggshell calcification refers to a ring of calcification around the periphery of a lymph node and is said to be a very characteristic sign but seen only in a minority of cases (3%–6%) of silicosis.[⁷]

To differentiate it from calcification along the borders as well as ring shadows due to end-on view of the large bronchi, Jacobson et al.[⁸] described the diagnostic criteria for eggshell calcification as follows:

1. Shell-like calcification up to 2 mm thick must be present in the peripheral zone of at least two lymph nodes
2. The calcification may be solid or broken
3. In at least one of the lymph nodes, ring-like shadow must be complete
4. The central part of the lymph node may show additional calcification
5. One of the affected lymph nodes must be at least 1 cm in its greatest diameter.

All the above criteria were met in the present case. The diagnosis was established on the basis of clinical, the characteristic radiological picture and the occupational history of stone cutting. While eggshell calcification with bilateral progressive massive fibrosis is classically seen in silicosis and also in coal worker's pneumoconiosis, it may occasionally be observed in sarcoidosis, scleroderma, postirradiation in Hodgkin's lymphoma, blastomycosis, histoplasmosis, and amyloidosis.[⁷]

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Conflicts of interest

There are no conflicts of interest.