Several bronchoscopic cryosurgical techniques are employed for diagnosis and as an adjunct to treatment for various pulmonary diseases. There has been an exponential increase over the past decade in the data regarding the diagnostic utility, technique, and safety of bronchoscopic cryosurgery with a growing number of interventional pulmonologists and thoracic surgeons performing these procedures.

Bronchoscopy-guided transbronchial cryobiopsy (TBCB) is a useful tool in diagnosing parenchymal lung diseases; it has been proposed as an alternative to surgical lung biopsy (SLB) in the diagnosis of interstitial lung diseases (ILDs) since early 2009 [1]. In selected patients with ILD who require a histological diagnosis, lung biopsies were traditionally obtained by surgery or bronchoscopically via the transbronchial forceps technique. This patient cohort often has multiple comorbidities and compromised ventilatory capacity which puts them at higher risk of having complications including death from invasive surgical procedures [2]. Transbronchial forceps biopsy (TBFB) often lacks sufficient quality due to small size and crush artifacts and has a lower yield in diagnosing ILDs [3,4,5]. TBCB is relatively new and is becoming widespread with a reported accuracy of approximately 80% in diagnosing ILDs [6,7,8,9]. This high accuracy rate, combined with its minimally invasive nature, makes it an attractive alternative to traditional SLB.

A flexible cryoprobe is a useful tool for the diagnosis of lung cancer as well as for therapeutic bronchoscopy, in particular, for cryo-recanalization in patients with central airway obstruction (CAO). Cryobiopsy has a diagnostic accuracy rate of up to 95% for endobronchial tumors [10] and approximately 90% for peripheral pulmonary nodules [11,12], making it a useful tool for diagnosing lung cancer in its early stages, when treatment is most effective.

ILD is a broad term encircling a group of lung diseases that are often difficult to diagnose. In recent years, multidisciplinary team discussions (MDD) have overtaken the previous gold standard of SLB. They are a vital process and remain a critical step in the diagnostic pathway, improving diagnostic confidence [16]. Usually, a consensus diagnosis is made by MDD after reviewing clinical and radiological data but occasionally histopathological specimens are required when evaluating these patients [16,17]. Radiological guidelines report that a diagnosis of idiopathic pulmonary fibrosis (IPF) can be made without an SLB in selected cases when computed tomography (CT) shows a probable usual interstitial pneumonia (UIP) pattern [18]. However, for patients with CT features indeterminate for UIP or when the CT is suggestive of an alternate pathology and the ILD remains unclassifiable, diagnostic tools, and techniques to obtain tissue specimens may be needed for definite diagnosis. An ideal test is one which achieves the principal goal of adequate diagnostic tissue, is minimally invasive, cost-effective, can be carried out as an outpatient, and has a good safety profile.

International clinical practice guidelines, published in 2018, recommend SLB for obtaining a histopathological diagnosis and do not include TBCB in the diagnostic algorithm for ILD [27]. However, the role of TBCB was not discouraged in the same guidelines. In 2020, the American College of Chest Physicians (ACCP) Guidelines and Expert Panel Report did conclude that TBCB is a reasonable alternative to SLB for providing histology for ILD MDD [28].

TBCB yields specimens sized between forceps and surgical biopsies, hence balancing the increased diagnostic yield of the latter with the safety of the former [29,30]. The histopathologic assessment of cryobiopsy-obtained tissue samples undergoes the same pathological assessment as those obtained via traditional methods, like SLB or TBFB [29,31]. This includes processing, fixing, and staining with hematoxylin-eosin, elastica van Gieson, and Prussian blue along with any specific antibodies vital to immunohistologic diagnosis [32,33,34,35]. Analysis usually begins with the microscopic examination at low power to determine the presence of a histological pattern, then the pattern and differential diagnoses are correlated with the clinical and radiologic findings to complete a multidisciplinary approach which has been shown to increase the diagnostic yield [31,34].

When analyzing a cryobiopsy specimen, consideration must first be given to the artifacts or inclusions that may deter a pathologist from making a diagnosis. Cryobiopsy has been shown to have fewer frozen artifacts when compared to cryostat sections, and while they may lack enough detail in the nuclear and cytoplasmic features, this does not have a significant effect on pathologic interpretation [29]. Further, the cryobiopsy technique minimized the inclusion of crush artifacts usually seen in samples obtained via conventional TBFB [30,34,35]. The trauma to the tissue that occurs while obtaining a biopsy may lead to the inclusion of adjacent tissue such as bronchial epithelium, visceral pleura, parietal pleura, intra-alveolar material, skeletal muscle, vessels, or blood from procedure-induced hemorrhage [24,29,34,36]. Hemorrhagic artifacts are often focal findings that do not interfere with pathologic interpretation, but if the artifact is extensive, it may inadvertently lead to the suspicion of an acute lung injury [34]. Depending on the angle of the biopsy, airways may take up a large portion of the tissue sample, especially in patients with obstructive airway diseases, and thus multiple biopsies (3–5 samples per lobe) with large surface areas should be taken [29,34]. Care should be taken to ensure that the bronchoscope fully passes the smallest subsegment and is placed in the outer one-third of the lungs in order to obtain alveolar tissue and minimize the bronchial wall [34]. Common causes of a nondiagnostic sample obtained via cryobiopsy are either the presence of bronchial wall tissue or of normal lung parenchymal tissue, both often due to procedural error in sampling, likely stemming from the lack of procedural standardization [31,34,37].

When analyzing for histological patterns, the smaller size of the sample may be a hindrance but typical patterns are clearly visible as long as the samples obtained are at least 5 mm [29,31,33,38]. The diagnosis of UIP can be made via the identification of patterns like honeycombing, patchy fibrosis, and fibroblastic foci, the visualization of which can be impaired by the presence of crush artifact or small sample size when obtained by TBFB [29,30,33,34]. A study by Casoni et al. showed that, of all the instances of TBCB in UIP and IPF, only 8.7% were considered non-diagnostic [30]. A similar diagnostic rate was claimed by Hagmeyer et al. who showed that 91% of the TBCB samples were indicative of the initial diagnosis with 72% requiring no further diagnostic intervention [32].

Similarly, patterns of fibrosis consistent with nonspecific interstitial pneumonia (NSIP) were easily identified via cryobiopsy samples and demonstrated a high diagnostic yield [34]. The same can be said for non-necrotizing granulomas, Langerhans histiocytes, and stellate lesions in samples obtained for suspicion of sarcoidosis [29,34,39]. When investigating eosinophilic pneumonia, cryobiopsy was able to produce a sample lacking any crush artifacts that allowed the identification of lymphoid follicles, septal widening, giant cells, and eosinophilic nests in levels rivaling samples obtained via surgical biopsy [29,32,34]. Samples obtained for the suspicion of subacute hypersensitivity pneumonitis were able to clearly demonstrate bronchiolocentric accentuation, non-necrotizing granulomas, and septal chronic inflammation at levels high enough to make a confident and definitive diagnosis [34].

With the above considerations, cryobiopsy has been shown to have a diagnostic yield in the close to 90% range, approaching the confidence of surgically obtained biopsies while minimizing complications [8,33,34,36,37].

Lung cancer is one of the leading causes of cancer-related deaths worldwide [40]. With the advent of targeted therapies especially for non-small cell lung cancer (NSCLC), survival has improved [41]. However, this is an aggressive malignancy, and timely diagnosis and initiation of treatment are pivotal. Obtaining adequate tissue samples is key for the diagnosis and subtyping of cancers to guide further management. Inadequate biopsy specimens may require repeat procedures and delay management. This can compromise treatment and patients may miss the window of opportunity for cure [42]. Furthermore, there are extra costs involved in repeat procedures which adds a financial burden on the health system.

Endoscopic procedures are minimally invasive and are the preferred initial investigation for the diagnosis of lung cancer. EBUS-guided TBNA is an excellent minimally invasive tool for obtaining a cytologic diagnosis for mediastinal lesions. The literature reports a diagnostic yield of standard linear EBUS of around 89–93.5% [43,44,45]. However, in the era of targeted therapies especially for NSCLC, adequate tissue is essential for molecular analysis and ancillary testing. Furthermore, rare tumors or hematological malignancies such as lymphoma may require a core biopsy rather than a fine needle aspirate to obtain a larger tissue sample and a histological diagnosis. Zhang et al. showed that cryo-biopsy may be a useful adjunct to diagnostic bronchoscopy for mediastinal lesions. They safely carried out a randomized trial of EBUS-guided TBNA and TBCB for mediastinal lesions in 196 patients. They reported improved diagnostic yield with TBCB as compared to conventional TBNA (91.8% vs. 79.9%, p-value = 0.001) [46].

TBCB is emerging as an adjuvant tool to radial EBUS (r-EBUS) in diagnosing peripheral pulmonary lesions (PPLs). A recent large observational study included 1024 patients with PPLs ≥ 2 cm in size. PPLs were localized with r-EBUS, fluoroscopy, or both and TBCB was performed. TBCB appeared safe with a relatively low complication rate; significant bleeding occurred in 3.5% of cases and pneumothorax requiring drainage occurred in 6.6% of patients. The diagnostic yield of TBCB was 91%, [11]; this is a great improvement on the reported yield of around 70% with standard biopsies via navigational techniques such as r-EBUS and electromagnetic navigation (EMN) [47,48]. Torky et al. showed that r-EBUS-guided TBCB is a safe and effective technique with a higher diagnostic accuracy and better-quality samples compared to forceps biopsies [49]. Nasu et al. [50] compared TBCB and TBFB under r-EBUS guidance for 53 PPLs and showed no significant difference in diagnostic yield (86.8 vs. 81.1%, p-value = 0.6). However, on further analysis, all tests on patients who tested positive for TBFB and negative for TBCB were performed without a guide sheath (GS) and TBCB carried out with GS had a better diagnostic yield than without GS. Oberg et al. [51] retrospectively analyzed 112 patients with 120 PPLs who had a biopsy via robotic bronchoscopy. Patients had TBNA followed by TBFB and a TBCB with a 1.1 mm cryoprobe. Overall diagnostic yield was 90%; out of these, TBNA was positive at 31.5%, TBFB at 77.8%, and TBCB at 97.2%. TBCB yielded a diagnosis exclusively in 18% of the cases and samples were adequate for molecular analysis. Hetzel et al. demonstrated that obtaining an endobronchial cryobiopsy had a superior diagnostic yield when compared to traditional forceps biopsy (95 vs. 85.1%, p-value < 0.001) [10].

An adequate sample size is often required to perform molecular testing and cryobiopsy appears feasible for diagnostic assessment in lung cancer. Nishida et al. obtained conventional scalpel biopsy and cryobiopsy in 43 surgically resected primary lung tumors. Samples were prepared for immunohistochemical stains and a high concordance between the two sampling techniques was observed for certain tumor markers including programmed cell death ligand 1 (PD-L1) [52]. Furthermore, bronchoscopic cryobiopsy can increase the detection of epidermal growth factor receptor (EGFR) mutation in comparison to other tissue sampling techniques [53]. Given the cytotoxic effects of extreme cold on living tissue, cryotherapy can also be used for the treatment of endobronchial tumors, in particular, in-situ carcinomas, early-stage lung cancers, or stalks of resected tumors [54]. Lastly, due to its well-preserved specimens, cryobiopsy has been shown to be diagnostic for malignant pleural mesothelioma when conventional methods have previously failed [35].

CAO from a tumor is a life-threatening emergency and can result in death from atelectasis, respiratory failure, or pneumonia. Tumor debulking to relieve CAO can be achieved by laser, argon plasma coagulation (APC), mechanical endoscopic debridement, or cryorecanalization. There is a risk of airway fire with APC or laser which requires a reduction in oxygenation whilst these modalities are being applied. This can be challenging in patients with CAO who often present with respiratory failure and have compromised ventilatory capacity. Cryotherapy offers the advantage of maintaining oxygenation during the procedure, given that this works via a freezing effect, hence no risk of airway fire. Furthermore, cryotherapy equipment is less expensive than laser, making it a cost-efficient method for palliation of CAO. A cryoprobe can be introduced via flexible or rigid bronchoscopy into the tumor which is frozen and then extracted piecemeal. Schumann et al. reported successful cryorecanalization and rapid improvement from CAO in 91.1% of 225 patients. Moderate bleeding occurred only in 8% of patients which was controlled with APC or bronchial blocker [55]. A systematic review of 16 studies on endoscopic cryotherapy showed an approximately 80% success rate from cryorecanalization of CAO. In this review, most studies looked at patients with advanced inoperable lung cancer and the cryotherapy resulted in a statistically significant improvement in dyspnea, stridor, lung function, and quality of life scores [56].

Massive pulmonary hemorrhage, regardless of the etiology, can cause tracheobronchial obstruction from blood clots and life-threatening ventilatory failure. Bronchoscopic cryoextraction can facilitate the removal of blood clots and mucus plugs [57]. Small case series have shown that this can be achieved via flexible or rigid bronchoscopy to relieve tracheobronchial obstruction and provide improvement in ventilation [57,58,59,60]. Similarly, the cryo-adhesive effect on objects with water content can facilitate the extraction of foreign bodies from airways and its use has been described in multiple case reports [57,61,62]. Foreign bodies without enough water content can be extracted by spraying saline on the object followed by immediate freezing by the cryoprobe.

In recent years, the number of lung transplants has increased worldwide. However, graft dysfunction rates in lung transplantation recipients continue to be high with post-transplant rejection commonly seen as one of the major contributors [63,64]. The International Society for Heart and Lung Transplantation reports 28% of lung transplant recipients experience at least one episode of acute rejection in the first year following transplantation [65]. For this reason, lung transplant recipients undergo routine surveillance lung biopsies. Conventionally, TBFB has been the main technique to establish the presence of lung allograft rejection (AR) but there has been a trend towards TBCB in recent years.

Although the data available is limited, the above studies show that TBCB can be safely performed in lung-transplantation recipients and provides larger specimens with increased diagnostic yield.