Intrathoracic hybrid lesion: an incidental finding in a patient with PHACE syndrome

Abstract

Hybrid lesions (HLs) are unique, congenital lung malformations with both cystic and solid components and vascular supply consistent with bronchopulmonary sequestration. Increase of HLs reported in recent literature suggest a common pathological mechanism occurring during embryogenesis, leading to occurrence of both malformations within a single lesion. Due to the unusual nature of HLs, gold standard approach for diagnosis is not very well-defined in the literature. We report a novel case of a 3-year-old girl with posterior fossa anomalies-haemangioma-arterial lesions-coarctation of the aorta-eye anomalies syndrome, who was found, on CT angiography, to have a previously missed HL diagnosis which was confirmed after surgical resection.

Background

Only 0.15%–6.4% of congenital lung malformations (CLMs) are attributed to bronchopulmonary sequestration (BPS), a segment of lung tissue supplied by an anomalous branch of systemic circulation that does not communicate with the tracheobronchial tree and is thus non-functional.¹ Another rare CLM—though more common than BPS—is congenital cystic adenomatoid malformation/congenital pulmonary adenomatoid malformation (CCAM/CPAM). CCAMs are hamartomatous lung lesions with incidence ranging from 1 in 11 000 to 1 in 35 000 live births, accounting for about 25% of CLMs.² In hybrid lesions (HLs), for which there is no published incidence, features of both BPS and CCAM occur within a single lung lesion. To reduce potential complications such as infection or haemorrhage, elective resection is recommended, even in asymptomatic patients. This also aids in differentiating tissue histopathology and characterisation of the pulmonary lesion.^{2 3}

We present a case of HL found incidentally in a 3-year-old patient with PHACE syndrome, after obtaining informed consent from parent. MRI monitoring of patient’s right-sided facial/cervical haemangioma detected what was initially presumed to be a bronchogenic cyst in the left lower lobe. Patient underwent subsequent CT angiography (CTA), which was consistent with HL, and diagnosis was eventually confirmed on pathologic examination of the lesion post-surgical resection.

Missing the arterial feeder to the HL found in this case could have been detrimental to the patient’s surgical resection outcome. Given our experience, to avoid missing an anatomically-significant finding for any suspected CLM, we recommend CTA as the imaging modality of choice.

Case presentation

A 3-year-old girl with posterior fossa anomalies-hemangioma-arterial lesions-coarctation of the aorta-eye anomalies (PHACE) syndrome presented with chief complaint of an incidental finding of an intraparenchymal cystic lesion detected on magnetic resonance imaging (MRI)–magnetic resonance angiography (MRA). She was diagnosed with PHACE syndrome at age 2, given her features of infantile haemangioma >5 cm diameter of the head, including scalp, ventricular septal defect (VSD) and small vertebral artery visualised on MRA.^{4 5} She did not have history of haemoptysis or recurrent pneumonias, stridor, wheezing or retractions. Physical exam was notable for a large, pale, violaceous, telangiectatic, soft vascular plaque spanning the entire sensory distribution of the fifth cranial nerve on the right side of the face, with distortion of the right ear, scalp, neck and upper chest. (figure 1) Prior treatment with propranolol did not resolve her facial haemangioma, making alternative diagnoses such as port wine stain in Sturge-Weber syndrome less likely. Murmur of VSD was audible at the left sternal border, which was previously diagnosed on transthoracic echocardiogram as part of her PHACE syndrome workup. Vital signs were normal.

Figure 1.

Patient’s facial haemangioma at birth (top row), 1 year of age (middle row) and 2 years of age (bottom row).

Her regular screening MRA and MRI with IV contrast revealed a well-defined intraparenchymal cystic lesion in the left lower lobe with no postcontrast enhancement and no evidence of arterial feeders, features consistent with intraparenchymal bronchogenic cyst. Follow-up imaging with CTA was obtained to both further define the extent and nature of the lesion, and guide surgical planning. CTA proved to be the superior imaging technique, as it revealed an arterial supply to the cystic lesion emerging from the thoracic aorta and pulmonary venous drainage, consistent with an HL (figure 2).

Figure 2.

An axial CTA at the cardiac base level shows a solid and cystic HL with the arterial supply off the aorta (arrow). CTA, CT angiography; HL, hybrid lesions.

Outcome and follow-up

The patient was referred to paediatric surgery and underwent successful thoracoscopy-guided resection without complication. Gross pathology showed dark red, diffusely congested extralobar sequestration adhered to a smooth, white-tan, thin-walled cystic component of 2.0 cm in greatest dimension, keeping with HL. The sequestration component was connected to the aorta by two aberrant arteries, and the cystic component was connected to lung by a narrow parenchymal band and a few loose adhesions (figure 3).

Figure 3.

A coronal reconstruction at the level of the descending aorta shows the venous drainage (arrow) into the pulmonary vein (PV).

Discussion

HL is a combination of CCAM/CPAM and BPS. BPS is a segment of non-functioning lung tissue supplied by an anomalous branch of the descending aorta that does not communicate with the tracheobronchial tree, as seen in the lesion in the lower lobe of the left lung in our patient which had a systemic arterial feeder (figure 3).² Alternatively, CCAM/CPAMs consist of abnormal bronchial proliferation which has not been shown to preferentially occur in a particular region of either lung. These lesions are often continuous with the tracheobronchial tree and can have venous drainage into pulmonary circulation, as seen in the cystic component of the CLM in our patient. CLM complications include haemoptysis, haemothorax, recurrent pneumonias and malignant transformation, and may enlarge enough to cause mediastinal shift and abnormal alveolar development of adjacent pulmonary tissue.^{2 6}

CLMs likely develop secondary to gestational insult during weeks 7–17. Because of the potential for malignant transformation, these should be resected even when asymptomatic.²

MRI–MRA effectively visualises the cystic, solid, fluid, haemorrhagic and mucus-containing components of lung lesions. However, due to respiratory motion artefact, it may not accurately evaluate these abnormalities.¹ CT has become the imaging modality of choice, as it is a non-invasive, rapid test that produces high-resolution images and effectively detects a systemic feeding vessel with 93% sensitivity (95% CI 80% to 98%) and 88% specificity (95% CI 76% to 96%).³

As seen in our patient, CTA successfully identified the HL in comparison to previously done MRI–MRA, which misdiagnosed the CLM only as a cystic lesion. MRI–MRA reported a CCAM in the left lower lobe with no postcontrast enhancement or evidence of arterial feeders. Had CTA not been done, correct diagnosis would not have been reached prior to surgical planning for resection. Although CTA involves more ionising radiation than MRA, both require contrast to better define the blood vessel supply. MRI–MRA requires significantly longer testing time and associated sedation-related risks for most paediatric patients, which is the primary population we are concerned about in evaluating these congenital lung anomalies. All of these factors and findings further reinforce the choice of CTA as the first-line diagnostic imaging modality for the correct characterisation and diagnosis of CLMs.

PHACE is an acronym that represents a group consisting of the following abnormal findings: posterior fossa, haemangioma, arterial, cardiac/aortic coarctation and eye.⁷ PHACE syndrome is diagnosed by very specific major and minor criteria detailing particular arterial anomalies, structural brain lesions, cardiovascular malformations, ocular manifestations and ventral/midline anomalies that are not the focus of this case report and thus will not be detailed here.^{5 8}. In general, PHACE syndrome is diagnosed in a patient with a large haemangioma, usually of the face or neck, in combination with at least one other birth defect.^{5 7}

While CCAMs typically occur sporadically, they have been found in association with cardiac and renal anomalies in 15%–20% of cases.² In an 8-year retrospective review, 36 patients were diagnosed prenatally via ultrasound—and confirmed histopathologically—to have congenital cystic lung lesions (CCLLs), and nine of these CCLLs were found to be HLs. This same study found it is atypical to find CCLLs in association with other congenital malformations.³ Our literature search revealed no cases of BPS, CCAM, or HL, ever being reported in a patient with PHACE syndrome, which is part of what makes this case so unique.

Learning points.

• This case describes the typical presentation of a rare clinical syndrome. Posterior fossa anomalies-hemangioma-arterial lesions-coarctation of the aorta-eye anomalies (PHACE) syndrome consists of posterior fossa abnormalities, haemangiomas, arterial, cardiac and eye abnormalities.

• This case highlights the first reported case of a patient with PHACE syndrome being found to have a hybrid lung lesion.

• This case highlights the importance of CT angiography in correctly identifying arterial feeders in hybrid lung lesions, which, if misdiagnosed, could be detrimental to patients’ surgical resection outcomes.