IIPs as one of ILD include a subset of diffuse lung diseases [1].
The characteristic HRCT findings of reticular abnormality and honeycombing with basal and peripheral predominance are virtually diagnostic in the correct clinical context of UIP [20].
Quantitative CT analysis can be used as an objective tool for quantitative evaluation of disease extent [21]. It can be used to quantify fibrosis based on textural patterns for ground glass opacification, honeycombing, and reticulation [22].
This study involved 50 patients, referred to the Radiology Department at kasr Al-Ainy hospital from the chest outpatient clinic, with chronic chest complaint (dyspnea, dry cough, chest pain, finger clubbing). They were diagnosed as interstitial pneumonia. HRCT was done to all cases in the period between April 2017 and January 2019.
The mean age of the studied patients was 50.23 years with female predominance 86.7%.
The main clinical symptoms of our patient were as follows: dyspnea (76.7% of cases), chronic cough (43.3% of cases), and chest pain (36.7% of cases). We noted dyspnea was the commonest clinical symptom which was in agreement with the study done by Bonini et al. [23] who noted that dyspnea was one of the most common and disabling symptom in patients with ILD.
In the current study, among 50 cases of IIP, 40 cases were diagnosed as UIP, 5 cases as NSIP, 3 cases as LIP, and 2 cases as DIP according to HRCT-specific findings.
It was noted that usual interstitial pneumonia is the most common type of IIP 80%, which agreed with Koelsch et al. [24] who studied the idiopathic interstitial pneumonia according to its radiological findings, and agreed with Tanaka et al. [25] who studied the Update on Rare Idiopathic Interstitial Pneumonias according to histologic patterns; they both claim that UIP is the most common type of IIP.
In this study using color-coded images and semi-quantitative assessment of different HU allowed more objective evaluation of the degree of variable parenchymal affection in different interstitial lung disease.
Correlating the results of semi-quantitative CT assessment of parenchymal changes in interstital lung disease and PFT results showed the great advance in HRCT attribution in the accurate diagnosis and prognosis of interstitial lung disease.
As well as color-coded images allowed definite diagnosis of early diffuse ground glass opacification which used to be a subjective diagnosis.
Semi-quantitative CT assessment of honeycombing, ground glass, reticular opacities, emphysema, and normal lung showed the mean total volume of normal lung, ground glass, emphysema, reticulation, and honeycombing to be 21.15, 23, 22.09, 18.7, and 14.88, respectively. which is matching to result of Yagihashi study who found reticulation, ground glass, and honeycombing mean volume of 30.1, 21, and 9.1 respectively [26].
The honeycombing is considered the most specific sign of UIP as we noted honeycombing mostly found in UIP than other types of IIP [27] (Fig. 4).
NSIP is characterized by predominantly basal ground glass opacity and reticular pattern, often with traction bronchiectasis [28] (Fig. 5).
In our study, in patients with NSIP, we noted ground glass pattern opacities are the most common QCT finding (mean 23) and honeycombing is the least common finding (mean 6.1) (Fig. 6). Escalon et al. agreed with our result; he noted that NSIP is characterized by symmetric lower lobe predominant ground glass abnormality and honeycombing is a rare finding in NSIP [29].
LIP in our study had the least QCT finding of honeycombing (mean 5.6) which is in agreement with Kokosi et al., who noted honeycomb change is notably rare or absent in LIP [30] (Fig. 7).
In our study, all patients were subjected to spiometers PFT with emphasis on FVC%, FEV1%, and FEV1/FVC%; we noted that:
FVC (mean 75.74) has mild reduction indicating restrictive lung diseases, which agrees with Moon et al. and Jacob et al., with FVC mean 76.5 ± 18.2, 71% respectively [3, 31].
Also in our result, FEV1% and FEV1/FVC% with mean 52.82 and 69.14 respectively revealed moderate to severe reduction indicating obstructive lung diseases which yielded different results with those of Nakagawa et al., who showed FEV1% and FEV1/FVC% with mean 81.9 ± 18.7 and 80.5 ± 8.3 respectively [32].
In the present study, we aimed to compare the percentage of honeycombing, ground glass, emphysema, and reticular opacities to total normal lung volume measured with the help of semi-quantitative CT analysis, and correlate it with the pulmonary function tests (FVC% , FEV1%, FEV1/FVC%).
By correlation between semi-quantitative CT and spirometer PFT, we found as follows:
Honeycombing % had significant inverse correlation with FVC% (r = − 0.448, p values = 0.013), FEV1% (r = − 0.652, p values = < 0.001), and FEV1/FVC% (r = − 0.551, p values = 0.002). Nakagawa et al. agrees with our result, which found significant correlation between honeycombing and PFT “significant inverse correlation with FVC% (r = − 0.60, p value = 0.001) and FEV1% (r = − 0.66, p value = < 0.001) and signification correlation with FEV1/FVC% r = 0.20, p values = 0.322)” [32].
Reticular opacities % also had significant inverse correlation with FVC% (r = − 0.376, p value = 0.041) which agreed with Park et al.’s study which found negative correlation between RO and FVC (r = −VC (d wp value = < 0.001) [33].
Yoon in his study showed insignificant correlation between honeycombing %, reticular opacities %, and PFT which showed different results from our study [34].
Normal lung was significantly correlated with FVC% (r = 0.455, p value = 0.011), FEV1% (r = 0.691, p value = < 0.001), FEV1/FVC% (r = 0.753, p value = < 0.001) that is matching with Moon’s study which showed a very strong positive correlation with functional lung volume and FVC% (r = 0.72, p < 0.01) [31].
Shin et al.’s study also agreed with our study, which showed a high positive correlation with FLV and a high positive correlation with FVC and FEV1 (r = 0.80 and 0.73, p < 0.01) [21].
Insignificant correlation between PFT and ground glass %, emphysema %, and PFT (p values more than 0.05) agrees with Yoon’s study which showed insignificant relation between ground glass %, emphysema %, and PFT [34].
Park ’s study found that there is a negative correlation between the GGO% and FVC (p < 0.001), whereas the emphysema % correlated positively to the FVC with statistical significance (p < 0.001) which yielded a different result than ours [33].