Unusual localization of a choroid plexus papilloma in a 4-year-old female

Introduction 

Choroid plexus papillomas account for less than 1% of all intracranial tumors but represent 2-4% of those manifesting in children, with the majority of patients younger than 3 years of age [1], [2]. In children, choroid plexus papillomas develop most often in the lateral ventricles, whereas in adults these tumors are predominantly located in the fourth ventricle [1], [3]. Rare cases of ectopic choroid plexus papillomas have been described [4].

Most often children present with symptoms of intracranial hypertension including vomiting or increasing head size. Magnetic resonance imaging reveals a hyperdense contrast-enhancing lesion [2].

Macroscopically, choroid plexus papillomas are firm reddish-brown to pinkish masses with a cauliflower-like surface. Usually they are well-delineated from the surrounding brain tissue, but they may extend into it without frank invasion. Histopathologically, choroid plexus papillomas closely resemble nonneoplastic choroid plexus with cells more crowded and elongated than usual. Malignant features, such as increased mitotic activity and brain invasion, are absent [5], [6]. The treatment of choice is complete excision of the tumor, which is curative [7], [8].

In this report, we present a 4-year-old-female with a 2-year-long history of intermittent vomiting who was diagnosed with a choroid plexus papilloma originating from the median rostral medulla oblongata.

Case report 

Our patient is the first child of healthy nonconsanguinous parents. She was born after an uneventful pregnancy via spontaneous vaginal delivery in good condition with a head circumference of 35.5 cm (sixty-fifth percentile). Initially she was a healthy child with a normal development. At 18 months of age, she began to have intermittent episodes of vomiting several times daily every other month, which were not associated with an intercurrent illness. Usually the following day she was back to normal and no treatment was initiated. Further investigations including a cranial computed tomography scan were not performed.

In August 2001 the vomiting increased in frequency to every other week. She was observed at a local hospital and a cranial magnetic resonance imaging scan was recommended. Symptoms settled initially but reoccurred in December 2001 and the child was referred to our hospital.

The physical examination revealed a 4-year-old female in good physical and mental health (weight: 14.3 kg, twenty-fifth percentile, height: 97.6 cm, head circumference: 48.4 cm, both tenth percentile). Eye examination did not reveal papilledema. She had no cerebellar symptoms, such as ataxia, nystagmus, or intention tremor. Her muscle tone was normal, her deep tendon reflexes were symmetric, although not exaggerated, and her Babinski’s response was negative bilaterally.

The cranial magnetic resonance imaging scan did reveal a large solid tumor that extended into the cisterna magna and the lower part of the rhomboid fossa with prominent contrast enhancement (Figs 1A, B). The fourth ventricle was slightly elevated and enlarged. A magnetic resonance imaging scan of the spine did not reveal metastasis. Magnetic resonance angiography was not performed.

View Large Image Download to PowerPoint

Figure 1. Cranial magnetic resonance imaging by T1-weighted images before and after surgery. (A) Horizontal view of the cerebellum and pontomedullary junction illustrates a large contrast-enhancing lesion in the posterior fossa (TR = 429 ms, TE = 12 ms). (B) Sagittal view of the same tumor. Note the absence of dilated third and lateral ventricles (TR = 429 ms, TE = 12 ms). Insert a: In the horizontal view the margin of the resected choroid plexus papilloma is located in the brainstem (TR = 429 ms, TE = 18 ms). Insert b: Sagittal view after surgery shows the removal of the tumor with a thin strip of tissue remaining (TR = 379 ms, TE = 25 ms).

A suboccipital craniotomy was performed and most of the tumor was excised. The intraoperative view revealed a tumor with an exclusive longitudinal origin at the midline of the floor of the fourth ventricle. The cerebellar tumor surface was completely separated from cerebellar hemispheres and vermis tissue. Magnetic resonance imaging 2 days after surgery confirmed the removal of the tumor with a thin strip of tissue remaining (Fig 1A, B).

Macroscopically the tumor had a cauliflower-like appearance. The histologic examination demonstrated a monomorphic solid tissue with a papillary growth. Compared with normal plexus epithelium the density of the tumor cells was increased. Above the stroma of the tumor, which was widened in some parts, the cells were located in single layers. The round to oval nuclei of the tumor cells were mainly situated at the basal part of the cells showing fine dispersed chromatin (Fig 2). Immunohistochemically, most cells stained positive for cytokeratin (1:500, Immunotech, Marseille, France) and S-100 protein (1:200, DAKO, Carpenteria, CA). Few cells were positive for vimentin (1:300, DAKO) and for the glia fibrillary acidic protein (1:50, DAKO). The tissue did not stain for epithelial membrane antigen (1:50, ImmunStain, Llarberi, UK) or carcinoembryonic antigen (1:25, Immunotech). The Ki-67 (1:100, Dianova, Hamburg, Germany) proliferation index approximated 1%. The definite diagnosis was a choroid plexus papilloma WHO grade I.

View Large Image Download to PowerPoint

Figure 2. Histologic features of the choroid plexus papilloma. Hematoxylin and eosin staining reveals a solid tumor with a high density of cells with similar morphology growing in a papillary fashion (×20).

After surgery the female recovered well and was released in good condition with recommendations for follow-up magnetic resonance imaging studies.

Discussion 

Choroid plexus papillomas originate from cells forming the choroid plexus and cause symptoms including vomiting and excessive head growth, which results either from obstruction of the ventricular outflow tracts or excessive production of cerebrospinal fluid. In children, they are predominantly located in the lateral ventricles. Only in rare instances ectopic choroid plexus papilloma (i.e., intraparenchymal or suprasellar) have been described [5].

We present a 4-year-old female with intermittent vomiting who was found to have a homogeneously enhancing mass in the fourth ventricle. Initially it was unclear whether the tumor originated from the cerebellar vermis or the brainstem. The differential diagnosis given the magnetic resonance imaging appearance was low-grade astrocytoma, medulloblastoma, brainstem glioma, or choroid plexus papilloma/carcinoma. At the time of surgery the tumor was found to be attached to the medulla oblongata and received all its blood supply from vessels coming from the brainstem.

Histologically the tumor fulfilled all the criteria of a choroid plexus papilloma, which was composed of uniform cuboidal to columnar epithelia. Malignant features, such as increased mitotic activity, brainstem invasion, and necrosis, were absent. The tumor stained positive for cytokeratin and vimentin, which are expressed by virtually all choroid plexus papillomas [6]. Additionally, markers including glial fibrillary acidic protein, which are typically absent in normal choroid plexus, and the S-100 protein were both detectable [6].

Choroid plexus starts to develop from proliferation of the ependymal cells that outline the ventricular system at an early ontogenic stage. Mitosis and differentiation are thought to be induced by the vascular core of the tela choroidea. The choroid plexus of the fourth ventricle appears at approximately the forty-eighth day of gestation and is attached to the roof of the ventricle in a T-shaped fashion consisting of two adjacent longitudinal strands of plexus [9]. The transverse portion of the T extends into the lateral recess generally protruding through the aperture.

In our patient the tumor did originate from the ependymal lining covering the median rostral part of the medulla and most likely had already developed early in her life.

The choroid plexus papilloma did not produce overt signs of raised intracranial pressure, such as papilledema or increasing head size. This result was most likely because of the absence of tumor growth into the lateral recess of the fourth ventricle, ensuring the continuous flow of cerebrospinal fluid.

Before the removal of the tumor, the rostral medulla and the pons were pushed forward slightly. We speculate that the episodes of recurrent vomiting were triggered by pressure on the area postrema.

In summary, choroid plexus papillomas are relatively rare tumors that generally have an excellent prognosis if they originate from the choroid plexus of the ventricular system. The unusual brainstem localization of this choroid plexus papilloma and the inability to excise the tumorcompletely might alter what would be otherwise a good prognosis of choroid plexus papillomas.