Para-aortic haemangioma mimics paraganglioma on MRI

Background

Haemangiomas are benign neoplasms consisting of a cluster of blood-filled cavities that can develop anywhere in the body but are most commonly found on the skin of children. Intra-abdominal haemangiomas within the liver are common incidental findings on abdominal imaging with CT or MRI.1 The four types of haemangiomas include cavernous, venous, capillary type and mixed. Cavernous haemangiomas are the most prevalent and can be associated with a risk of haemorrhage.2 Vascular anomalies, which consist of both vascular tumours and vascular malformations are formally classified according to the 2014 International Society for the Study of Vascular Anbmalies (ISSVA) guidelines.3

Pheochromocytomas and paragangliomas are neural crest-derived neuroendocrine tumours that, like haemangiomas, are highly vascular.4 Pheochromocytomas originate in the adrenal medulla, and extra-adrenal paragangliomas (EAPs) arise from parasympathetic tissues outside of the adrenal gland (commonly in the head and neck along the glossopharyngeal and vagus nerves) or from extra-adrenal sympathetic-associated chromaffin tissue (sometimes referred to as extra-adrenal pheochromocytomas).5 Sympathetic paragangliomas are chromaffin-positive and commonly derive from sympathetic tissue near the inferior mesenteric artery or aortic bifurcation.4 Sympathetic paragangliomas typically produce catecholamines, resulting in a constellation of symptoms similar to adrenal pheochromocytomas (hypertension, diaphoresis, headache and palpitations).6 In contrast, parasympathetic paragangliomas are chromaffin-negative and rarely produce catecholamines.7

Diagnosis of sympathetic paraganglioma is supported by hyperintensity on a T2-weighted MRI scan, positive functional imaging on [¹³¹I] metaiodobenzylguanidine (MIBG) scintigraphy and a biochemical work-up documenting elevated plasma or 24-hour urine metanephrines.8 We present a rare case of para-aortic haemangioma mimicking a paraganglioma on imaging. In contrast to small haemangiomas, hormonally active paragangliomas require medical and surgical management, so accurate diagnosis is essential.

Case presentation

A 70-year-old man was referred after a CT scan for back pain revealed an incidental 1.8 cm left renal mass and suspected para-aortic lymphadenopathy. Medical history was significant for hypertension, diabetes and nephrolithiasis. Surgical history included multiple back surgeries, extracorporeal shockwave lithotripsy and ureteroscopic laser lithotripsy. The patient denied family history of genitourinary malignancies.

On physical examination, the patient had a mildly elevated blood pressure of 137/82 mm Hg despite taking three antihypertensive medications: amlodipine, hydrochlorothiazide and lisinopril. On review of systems, the patient denied headaches, palpitations or tremulousness. Resistant hypertension, the most common sign of sympathetic paragangliomas, increased our clinical suspicion for a catecholamine-producing tumour.9

Investigations

Since lymphadenopathy associated with a <2 cm renal mass would be atypical, an MRI was ordered for further anatomic assessment. It revealed a 1.8 cm Bosniak IIF cyst in the left kidney (figure 1) and a 2.8 cm T2-hyperintense solid para-aortic lesion near the origin of the inferior mesenteric artery (figure 2). Due to the size and nature of the left renal lesion, it was considered unlikely to have associated metastatic lymphadenopathy. Therefore, EAP came to the forefront of the differential diagnosis given the anatomical location and the classic ‘light-bulb’ appearance, that is, T2 hyperintensity on MRI.

Figure 1

These T2-phase abdominal MRI images depict the patient’s left renal cyst (red arrows) in coronal (A) and axial (B) perspectives.

Figure 2

These T2-phase abdominal MRI images depict a hyperintense abdominal lesion (red arrows) in coronal (A) and axial (B) cuts. The lesion is located anterior to the abdominal aorta and inferior vena cava as shown in the axial cut (B).

Twenty-four hour urine catecholamine collection was pursued for metabolic work-up. Results were within normal limits: metanephrine 496 μg/24 hours (normal: 122–676 μg/24 hours) and normetanephrine 140 ng/24 hours (normal: 90–315 μg/24 hours). Due to the strong suspicion of paraganglioma based on the MRI, MIBG scintigraphy (figure 3) was obtained for further work-up. Although there was evidence for increased uptake of tracer on the MIBG scan, interpretation of the scan was equivocal as the radiologist was unable to determine whether uptake was specifically in the left adrenal gland or para-aortic tissue. False positive MIBG scintigraphy is considered to be rare, but the limited spatial resolution of these scans makes precise localisation of uptake in close anatomic structures challenging.10

Figure 3

[¹³¹I] Metaiodobenzylguanidine (MIBG) scintigraphy images of the patient demonstrate increased uptake in the lower abdominal region of the patient, which was interpreted as an equivocal finding by the radiologist.

We considered the option of percutaneous biopsy to provide tissue diagnosis. CT or ultrasound-guided biopsy of paragangliomas can be useful to establish a diagnosis, but it is essential to exclude production of catecholamines prior to needle biopsy.11 Our interventional radiologist was concerned about the safety of biopsy for this para-aortic lesion due to intervening bowel. After counselling, the patient opted not to undergo biopsy.

In summary, a 2.8 cm para-aortic T2-hyperintense mass was identified in a hypertensive 70-year-old man with a low-risk Bosniak IIF renal cyst, a negative functional work-up for catecholamine metabolites and an equivocally positive MIBG scan that could not clearly localise uptake to the mass.

Differential diagnosis

The differential diagnosis for a solid para-aortic retroperitoneal mass is relatively broad and includes neoplastic (paraganglioma, lymphoma, metastatic lymphadenopathy, retroperitoneal sarcoma, germ cell tumours, haemangioma, carcinoid, mesothelioma, lipoma, lymphangioma) as well as non-neoplastic lesions (retroperitoneal fibrosis, non-Langerhans histiocytosis, extramedullary haematopoiesis).12

Treatment

After a detailed risk/benefit discussion with the patient, we opted to pursue active surveillance for the Bosniak IIF renal cyst. The adrenal gland appeared normal on the MRI, so no intervention was pursued (figure 4). Given our radiologist’s elevated suspicion that the uptake observed on MIBG scanning was localised to the para-aortic mass in addition to the radiologist’s reluctance to biopsy the lesion percutaneously, we opted for robotic-assisted laparoscopic resection of the mass to provide a definitive diagnosis.

Figure 4

These T2-phase abdominal MRI images of the patient’s adrenal glands (red arrows) in coronal (A) and axial (B) cuts.

Given the essentially negative catecholamine work-up of this lesion and close discussion with anaesthesia, we did not initiate alpha and beta blockade. Intravenous magnesium was used intra-operatively as an alternative measure. Magnesium demonstrates some alpha blockade and inhibits catecholamine release.13 In addition, it is a vasodilator and stabilises the cardiac membrane.13 14 Therefore, it has been used in cases of suspected catecholamine-secreting tumours.15 The mass was resected robotically without complication, and the patient was discharged home on postoperative day one.

Outcome and follow-up

Histological examination revealed a proliferation of relatively monotonous round endothelial cells with numerous vascular channels filled with erythrocytes, consistent with a haemangioma without evidence of malignancy.

The patient continues to do well more than 1.5 years postoperatively without complaints. His most recent CT scan 18 months postoperatively showed no change in the Bosniak IIF cyst and no evidence for recurrence at the site of haemangioma resection. He will continue to have yearly renal ultrasound assessment to follow his renal mass on active surveillance.