Applied Radiology

Prepared by Robert L. Emery, MD, CAPT USAF MC and Douglas P. Beall, MD, MAJ USAF MC of the Department of Radiology and Nuclear Medicine, The Uniformed Services University of the Health Sciences, Bethesda, MD; Justin Q. Ly, MD, CAPT USAF MC of the Department of Radiology, Wilford Hall Medical Center, Lackland Air Force Base, San Antonio, TX; and Matthew D. Frick, MD and Alan D. Hoffman, MD of the Department of Radiology, The Mayo Clinic, Rochester, MN.

CASE SUMMARY

Patient one is an infant boy born at 35 weeks gestation via cesarean section who suffered from respiratory distress syndrome. The patient required ventilatory support, subsequently developing bilateral pulmonary infiltrates with eosinophilia. The patient recovered and, at 7 months of age, underwent a skeletal survey for short stature and developmental delay; at this time, it was incidentally noted that the patient had evidence of cervical lung herniation. Work-up for developmental delay revealed a normal karyotype and metabolic screen. At 9 months of age, this patient developed a small-bowel obstruction secondary to a ventral umbilical hernia. Following laparotomy and repair of the obstruction, the patient's recovery was complicated by cytomegalovirus (CMV) colitis. No definitive cause for this baby's developmental delay was discovered prior to loss to follow-up.

Patient two is a female toddler with a medical history significant for neuroblastoma, which was treated with adrenocorticotropic horomone (ACTH), and stage II ganglioneuroblastoma. On a chest radiograph for follow-up of a recent pulmonary infection, congenital cervical lung herniation was detected. Review of prior films dating back to birth revealed that there was subtle evidence of lung herniation.

Patient three is an otherwise healthy male infant who underwent chest radiography for cough and fever. The finding of cervical lung herniation was made incidentally.

DIAGNOSIS

Congenital cervical lung herniation

DISCUSSION

As described by Morel-Lavallae in 1845, lung hernias are classified first by location: cervical, chest wall, or diaphragmatic; and secondarily by etiology: congenital, spontaneous, traumatic, or pathological. ¹ The most common etiology for lung herniation is trauma, but in the pediatric population, congenital or spontaneous lung hernias can also occur. A congenital hernia is described when the parietal pleura is intact, while a traumatic hernia is diagnosed if the parietal pleura is disrupted. Cervical herniation is the least common location of lung herniation. In patients <3 years of age with no history of recent trauma, herniations are thought to be either congenital or spontaneous. The hernias can be unilateral or bilateral (Figure 1) and are three times more common on the right. ²

If a defect is present in Sibson's fascia (Figure 2) and the intrathoracic pressure is increased, a cervical lung herniation may occur. The cupola of the lung protrudes into or through the fascia at the thoracic inlet. It is unknown if an inherent weakness in the fascia predisposes individuals to this type of hernia, and it is also uncertain whether individuals with apical lung herniations are at increased risk for other hernias secondary to a generalized fascial laxity. These questions were posed by Grunebaum and Griscom ³ after they noted the presence of two hernias elsewhere and a hydrocele in their small series.

Sibson's fascia, otherwise known as deep cervical fascia, suprapleural membrane, and membrana suprapleuralis, acts like a diaphragm across the thoracic inlet. Sibson's fascia originates from the transverse process of the seventh cervical vertebrae and inserts along the inner border of the first rib and costal cartilage (Figure 2). At the periphery, the thickened portion of the endothoracic fascia blends with Sibson's fascia. The fascia also blends into the parietal pleura and is often reinforced by the scalenus minimus muscle. Three superficial bands arise from the scalene prevertebral fascia and also strengthen Sibson's fascia. ⁴ These bands are the vertebromembranous with a C7 and T1 origin, the transversomembranous with a C7 origin, and the costomembranous with an origin at the neck of the first rib. All three insert on the first rib. If the scalenus minimus is not present, the latter two bands receive contributions from its remnants. The boundaries of Sibson's fascia are posteriorly and laterally the vertebral column, first rib, levator scapulae, and scalenus medius muscle; medially the superior mediastinal structures; and anteriorly the scalenus anterior and sternocleidomastoid muscles. ³

Cervical lung herniation is infrequently described in the literature, and most of the "herniations" found in the literature are actually protrusions. ⁴ Despite the lack of clarity in the nomenclature of these lung protrusions, little attempt has been made to delineate a hernia from a protrusion. The first distinction made between the two is that a true hernia is secondary to a tear or defects in Sibson's fascia and is very uncommon, while a protrusion is felt to be secondary to weakening of Sibson's fascia. Unfortunately, a tear or defect is indiscernible without surgery. ⁴ Also, because lung protrusions regress spontaneously, those bulges that do not regress or progress are labeled as hernias. Interestingly, most cases described as protrusions have a superior extent of no greater than C6, C7, or the superior margin of the T11 vertebral body.

Making the distinction more difficult, in 1978 Grunebaum and Griscom ³ described a case of a 3-month-old who had a cervical lung herniation to the level of C4 that regressed and disappeared in 2 years. We also note an apical lung herniation to the level of the C5 vertebral body, which reduced spontaneously on a subsequent radiograph 1 week later (Figure 3).

The cervical lung hernias can often be palpated in the neck or supraclavicular area, especially in situations in which intrathoracic pressure is increased. Crying, coughing, straining, and valsalva can all produce the characteristic mass that can give the patient a "frog-like" appearance. ⁵ Crepitation may be felt over the mass, but pain and hoarseness are notably absent.

It is recommended that the patient increase intrathoracic pressure by any of the aforementioned maneuvers during radiographic procedures. The frontal view often does not demonstrate the hernia, and a lateral neck film with valsalva is often the procedure of choice (Figures 3A and B). Spontaneous reduction may prevent radiographic spot film visualization (Figures 3C and 4A). Fluoroscopy with frontal and oblique views may aid in the diagnosis, especially with a young or uncooperative patient. The trachea often deviates away from the protrusion (Figure 4B), and in the lateral projection, the cervical trachea may be narrowed (Figure 3A).

Lightwood and Cleland ¹ stated, "the results of [surgical] repair are satisfactory provided that selection is restricted to those with a definite hernia." This opinion reinforces the need to develop objective criteria for differentiation between a cervical lung herniation and a lung protrusion. To date, there is poor criteria to differentiate between the two. Currarino ⁴ describes protrusions as not uncommon, seen often in the first 3 years of life, varying greatly in size without a separation between mild and severe forms, and the majority resolving before the age of 3. With these facts, it may be reasonable to state that those "protrusions" occurring after the age of 3 or those protrusions increasing in size from birth to age 3 may, in fact, be cervical lung hernias. Additionally, the bulk of the literature on cervical lung protrusions indicates that most of these protrusions do not extend superior to the C6 vertebral body. This seems reasonable given the anatomic location of Sibson's fascia, which extends from the transverse process of C7 to the inner border of the first rib (Figure 2). The prior reported cases in combination with this anatomic information would suggest that apical lung protrusions that extend more cephelad than the superior endplate of the C6 vertebral body would be more consistent with cervical lung herniations. This development of differentiating criteria should be considered important not only to decrease the potential morbidity from this entity but because of the satisfactory repair noted by Lightwood and Cleland ¹ whose patients were "restricted to those with a definite hernia."

Surgery is required only for those with persistent hernias because protrusions (and even some herniations) are noted to resolve spontaneously. A conservative approach to a presumed apical hernia is warranted, unless respiratory distress is noted. If the cervical lung herniation does not reduce, even with decreased intrathoracic pressure, the possibility of an incarcerated lung should be considered. If the lung herniation persists over time and does not regress, surgery is a viable option. A direct suture technique is used in small tears in Sibson's fascia while prosthetic materials may be used to repair larger tears. The transthoracic route is often used, although the alternate cervical route is advocated by some surgeons. ¹ Other indications for surgery include cosmetic repair and incarceration (although no case reports exist describing cervical lung hernia incarceration). Patients may also undergo surgery to reduce the risk of pneumothorax. Procedures such as tracheostomy and jugular and subclavian line placement also have higher theoretical complications given the closer proximity of the apex of the lung, and adequate caution must be exercised when performing thoracic interventional procedures in these patients.

CONCLUSION

The natural course for cervical lung hernias is not described in the literature, and there is substantial confusion in differentiating cervical lung protrusions from lung herniations. Complicating this distinction, there has been at least one reported case of spontaneous regression of a cervical lung herniation but no specific radiographic guidelines to differentiate between the two. Although most true cervical lung hernias occur after trauma, congenital and spontaneous cases do exist. Radiographically, differentiating between a herniation and a protrusion has traditionally been a matter of opinion, and deciding on a follow-up regimen versus surgical correction can often prove to be a difficult decision. Establishment of objective criteria for differentiating a cervical lung herniation from a protrusion will assist in determining the follow-up necessary (if any) and in formulating a treatment plan