Uncommon Presentation of Substernal Chylothorax Following Coronary Artery Bypass Grafting Without LIMA Harvest: An Atypical Case

Introduction

Cardiac surgery is a widely performed medical procedure globally, with over one million surgeries conducted annually [1]. Since the 19th century, the procedure has had remarkable advancements, including the development of various surgical techniques. Coronary artery bypass grafting (CABG) is the most frequently performed cardiac surgery, accounting for over 40% of all major cardiac procedures globally [2]. Despite the significant advancement in surgical techniques and perioperative care, CABG is still associated with several postoperative complications. Some of the most frequently encountered are wound infections, atrial fibrillation, graft failure, renal failure, and even mortality. Additionally, chylothorax can also occur in patients undergoing CABG.

Chylothorax is one of the rarest postoperative complications observed in patients undergoing CABG, with an incidence rate of 0.3 to 1.5% [3]. Despite its rarity, chylothorax presents a significant clinical challenge due to its potential severity. Generally, chylothorax can be broadly categorized into 3 leading causes: non-traumatic, traumatic, and idiopathic, with approximately two-thirds of all documented cases attributed to non-traumatic causes [4]. Chylothorax following CABG is most commonly associated with procedures involving thoracic cavity access, typically resulting in trauma to the thoracic duct during CABG utilizing the left internal mammary artery (LIMA) as a graft [5]. To the best of our knowledge, no previous reports have described the occurrence of substernal chylothorax in median sternotomy CABG, although substernal chylothorax related to an enlarged goiter has been previously reported.

Case Report

INVESTIGATIONS:

A swab culture of the drain fluid was performed on the same day, identifying the presence of Streptococcus mitis-oralis. Serial complete blood counts (CBC) obtained on postoperative days 3, 5, and 7 revealed persistently elevated white blood cell (WBC) counts of 19.3×10⁹/L, 15.7×10⁹/L, and 17.1×10⁹/L, respectively. Additionally, lymphocyte counts showed an upward trend, with values of 3×10⁹/L, 7×10⁹/L, and 12×10⁹/L over the same period. These findings raised the suspicion of a postoperative infection. However, the patient’s C-reactive protein (CRP) levels were relatively low for an active infection, measuring 77.3 mg/L on postoperative day 5 and 55.1 mg/L on day 7. Given the incongruity between the clinical and laboratory findings, surgical re-exploration of the substernal area was performed on postoperative day 8. During the exploration, no evidence of abscess or necrosis, and no active chylous leakage was observed. A thoracic drain was placed during the procedure, and the affected area was thoroughly cleaned using a vacuum. The intraoperative findings suggested a diagnosis of sternal wound infection.

On the first postoperative day following the second surgery, purulent drainage recurred. The drain output remained consistent at approximately 200 to 300 mL daily, with a clear purulent appearance in the morning (Figure 2). However, the drainage became cloudy following oral intake, suggesting that the source was not due to infection. By the fourth postoperative day, an antinuclear antibody (ANA) test was performed, which yielded negative results, and pleural lactate dehydrogenase (LDH) levels were elevated at 459 U/L. On the fifth postoperative day, blood and drain fluid cultures showed no microbial growth, and an interferon-gamma release assay (IGRA) was also negative, ruling out infectious or granulomatous etiologies. On the sixth postoperative day, triglyceride (TG) levels in the drain fluid were markedly elevated at 1054 mg/dL, and chylomicron analysis was positive, confirming the presence of chyle in the substernal drain. Additional investigations revealed an erythrocyte sedimentation rate (ESR) of 12 mm/h, 50 mg/dL cholesterol levels, and a negative anti-dsDNA antibody test. These findings collectively led to the final diagnosis of substernal chylothorax secondary to CABG.

DIFFERENTIAL DIAGNOSIS:

In this patient, the initial differential diagnosis focused on postoperative infection following CABG, prompted by changes in the character of the drain output and supported by an elevated white blood cell count, positive swab culture findings, and lymphocyte abnormalities. However, the consistently low CRP levels created a notable inconsistency within the inflammatory profile, raising doubt regarding infection as the sole explanation. Subsequent surgical re-exploration revealed persistent abnormal drain output, further prompting reconsideration of the initial diagnosis. The detection of markedly elevated LDH and triglyceride levels, along with the presence of chylomicrons in the fluid analysis, redirected the differential toward a lymphatic etiology. These findings ultimately supported the diagnosis of substernal chylothorax following CABG, despite the procedure not involving the LIMA.

TREATMENT:

Given the substernal drain output of 200 to 300 mL daily, a conservative management approach was initiated. The treatment regimen included a low-fat nutritional diet, partial parenteral nutrition, and wound debridement.

OUTCOME AND FOLLOW-UP:

Following this intervention, the patient’s condition showed gradual improvement, with a significant reduction in drain output. Nine days after the second surgery, vacuum-assisted closure (VAC) therapy was discontinued, and the wound was closed. The patient continued to receive conservative management, and after 11 days of treatment, he was discharged to outpatient care. The substernal drain remained in place at discharge, with a reduced output of approximately 50 mL over 24 h. After discharge, the patient underwent routine weekly outpatient follow-up. Seven days after leaving the hospital, the substernal drain was removed due to the absence of further drainage. The patient reported no problems during the second and third weeks of outpatient follow-up.

Discussion

Chylothorax is defined as the accumulation of chyle within the pleural cavity and can result from trauma, surgical complications, malignancy, or congenital abnormalities [6]. Several case reports have described chylothorax following coronary artery bypass grafting, most commonly associated with left internal mammary artery harvesting [3,7–11]. This association is explained by the anatomical proximity between the thoracic duct and the origin of the left internal mammary artery near the thoracic apex [12]. In the present case, however, left internal mammary artery harvesting was not performed, and the procedure was conducted via median sternotomy. The most plausible mechanism was injury to peri-thymic lymphatics or small mediastinal lymphatic vessels during surgical manipulation. Disruption of these small vessels likely resulted in low-output chyle leakage of approximately 200 to 300 mL per day. Another possible contributing factor is anatomical variation of the thoracic duct. The thoracic duct exhibits considerable variability in its origin, course, and termination [13]. Such variations can increase susceptibility to inadvertent injury during mediastinal dissection, even without direct manipulation of the classical thoracic duct pathway. Similar mechanisms have been reported by Okiljević et al, where chylothorax was attributed to injury of terminal thoracic duct branches near the left brachiocephalic vein [14]. Peri-thymic lymphatic injury has also been described in patients undergoing sternotomy for thymectomy rather than coronary bypass surgery [15].

Clinically, postoperative chylothorax typically presents as pleural effusion with a milky appearance. Definitive diagnosis relies on pleural fluid analysis demonstrating triglyceride levels greater than 110 mg/dL, lymphocyte predominance, and the presence of chylomicrons [16]. These findings were confirmed in our patient.

Due to its rarity, there is no universally accepted management guideline for postoperative chylothorax. Initial management includes adequate chest drainage to evacuate accumulated chyle [9,10]. Treatment strategies are generally divided into conservative and surgical approaches. Conservative therapy aims to reduce chyle production and consists of cessation of oral intake, initiation of total parenteral nutrition, and implementation of a low-fat diet rich in medium-chain fatty acids. Medium-chain fatty acids are absorbed directly into the portal circulation, bypassing the chylomicron pathway and thereby reducing chyle flow [17,18]. Pharmacologic agents such as somatostatin or octreotide may further decrease lymphatic secretion. Early initiation of conservative treatment improves success rates and reduces the need for reoperation [19].

However, conservative therapy may fail in high-output cases. Persistent drainage exceeding 1000 mL per day for 7 days or failure to reduce output below 200 mL per day after 2 weeks are commonly cited indications for surgical intervention [6,20–22]. In our case, clinical improvement occurred within 2 weeks, and surgical treatment was not required. Our updated recommended algorithm to diagnose and manage patients presenting postoperative chylothorax is presented in Figure 3.

In our case, clinical improvement occurred within 2 weeks, and surgical treatment was not required [22,23]. Percutaneous thoracic duct embolization is a less invasive alternative, with reported success rates of approximately 80% [24,25]. Adjunctive procedures such as pleurodesis may help prevent recurrence. This case highlights that chylothorax can occur after coronary artery bypass grafting even without left internal mammary artery harvesting, emphasizing the importance of recognizing alternative mechanisms of lymphatic injury and initiating timely management.

Conclusions

Post-CABG chylothorax can occur even without LIMA harvesting, although it is more commonly associated with LIMA-related procedures and occurs at a lower incidence in their absence. This phenomenon likely resulted from injury to the peri-thymic and small mediastinal lymphatics, as well as to the multiple terminal branches of the thoracic duct located near the left brachiocephalic vein. In this case, the diagnosis of substernal chylothorax presented a challenge due to its rarity. However, this case provides new insights into substernal chylothorax, offering valuable knowledge that should be considered in patients with purulent drain output and otherwise stable clinical conditions.